AHA/ACC/HRS Scientific Statement

Recommendations for the Standardization and Interpretation of the Electrocardiogram Part I: The Electrocardiogram and Its Technology A Scientific Statement From the American Heart Association and Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology

Paul Kligfield, MD, FAHA, FACC; Leonard S. Gettes, MD, FAHA, FACC; James J. Bailey, MD; Rory Childers, MD; Barbara J. Deal, MD, FACC; E. William Hancock, MD, FACC; Downloaded from Gerard van Herpen, MD, PhD; Jan A. Kors, PhD; Peter Macfarlane, DSc; David M. Mirvis, MD, FAHA; Olle Pahlm, MD, PhD; Pentti Rautaharju, MD, PhD; Galen S. Wagner, MD

Abstract—This statement examines the relation of the resting ECG to its technology. Its purpose is to foster understanding of how the modern ECG is derived and displayed and to establish standards that will improve the accuracy and http://circ.ahajournals.org/ usefulness of the ECG in practice. Derivation of representative waveforms and measurements based on global intervals are described. Special emphasis is placed on digital signal acquisition and computer-based signal processing, which provide automated measurements that lead to computer-generated diagnostic statements. Lead placement, recording methods, and waveform presentation are reviewed. Throughout the statement, recommendations for ECG standards are placed in context of the clinical implications of evolving ECG technology. (Circulation. 2007;115:1306-1324.) Key Words: AHA Scientific Statements Ⅲ electrocardiography Ⅲ computers Ⅲ diagnosis Ⅲ electrophysiology

by guest on October 18, 2017 Ⅲ intervals Ⅲ potentials Ⅲ tests

n the century since the introduction of the string galva- terpretation may lead to the recognition of electrolyte Inometer by Willem Einthoven,1 the electrocardiogram abnormalities, particularly of serum potassium and calcium, (ECG) has become the most commonly conducted cardiovas- and permit the detection of some forms of genetically cular diagnostic procedure and a fundamental tool of clinical mediated electrical or structural cardiac abnormalities. The practice.2,3 It is indispensable for the diagnosis and prompt ECG is routinely used to monitor patients treated with initiation of therapy in patients with acute coronary syn- antiarrhythmic and other drugs, in the preoperative assess- dromes and is the most accurate means of diagnosing intra- ment of patients undergoing noncardiac surgery, and in ventricular conduction disturbances and arrhythmias. Its in- screening individuals in high-risk occupations and, in some

Other members of the Standardization and Interpretation of the Electrocardiogram Writing Group include Mark Josephson, MD, FACC, FHRS; Jay W. Mason, MD, FAHA, FACC, FHRS; Peter Okin, MD, FACC; Borys Surawicz, MD, FAHA, FACC; and Hein Wellens, MD, FAHA, FACC. The American Heart Association, the American College of Cardiology, and the Heart Rhythm Society make every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on October 26, 2006, by the American College of Cardiology Board of Trustees on October 12, 2006, and by the Heart Rhythm Society on September 6, 2006. This article has been copublished in the March 13, 2007, issue of the Journal of the American College of Cardiology and in the March 2007 issue of Heart Rhythm. Copies: This document is available on the World Wide Web sites of the American Heart Association (www.americanheart.org) and the American College of Cardiology (www.acc.org). A single reprint is available by calling 800-242-8721 (US only) or writing the American Heart Association, Public Information, 7272 Greenville Ave, Dallas, TX 75231-4596. Ask for reprint No. 71-0389. To purchase additional reprints, call 843-216-2533 or e-mail [email protected]. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.americanheart.org/presenter.jhtml? Identifierϭ4431. A link to the “Permission Request Form” appears on the right side of the page. © 2007 American Heart Association, Inc., the American College of Cardiology Foundation, and the Heart Rhythm Society. Circulation is available at http://www.circulationaha.org DOI: 10.1161/CIRCULATIONAHA.106.180200 1306 Kligfield et al Standardization and Interpretation of the ECG, Part I 1307

cases, for participation in sports. As a research tool, it is used The ECG and Its Technology in long-term population-based surveillance studies and in The purposes of this statement are (1) to examine the relation experimental trials of drugs with recognized or potential of the resting ECG to its technology, (2) to increase under- cardiac effects. standing of how the modern ECG is derived and recorded, Indications for use of the ECG were summarized in a joint and (3) to promote standards that will improve the accuracy American Heart Association (AHA)/American College of Car- and usefulness of the ECG in practice. Special emphasis will diology report in 1992.4 Because of its broad applicability, the be placed on the digital recording methods and computer- accurate recording and precise interpretation of the ECG are based signal processing that are used in current electrocar- critical. The establishment of and adherence to professionally diographs to provide automated measurements that lead to developed and endorsed evidence-based standards for all phases computer-generated diagnostic statements. The writing group of the ECG procedure is an important step in ensuring the high recognizes that technical details of the processing and record- level of precision required and expected by clinicians and their ing of ECGs may be unfamiliar to clinicians. Accordingly, a patients.5 However, there has not been a comprehensive updat- major purpose of this document is to provide clinicians with ing of ECG standards and criteria since 1978.6–14 Since 1978, insight into the generally missing link between technology there have been many advances in the technology of electrocar- and its consequences for clinical ECG interpretation. The diography; in the understanding of the anatomic, pathological, evolution and application of ECG technology have profound electrophysiological, and genetic information underlying ECG clinical implications, as exemplified by the demonstration Downloaded from findings; and in the clinical correlations of ECG abnormalities. that measurements made by different automated ECG sys- One of the most important changes in electrocardiography is the tems from reference ECG data can vary enough to alter widespread use of computerized systems for storage and analy- diagnostic interpretation.15,17 Sensitivity and specificity of sis. Many if not most ECGs in the United States now are computer-based diagnostic statements are improving, but at recorded by digital, automated machines equipped with software the same time, it remains evident that physician overreading http://circ.ahajournals.org/ that measures ECG intervals and amplitudes, provides a virtually and confirmation of computer-based ECGs is required.15,16,18 instantaneous interpretation, and often compares the tracing to those recorded earlier by the same system. However, different Previous Standards and Reviews automated systems may have different technical specifications A number of recommendations for the standardization of that result in significant differences in the measurement of ECG recording and guidelines for ECG interpretation in the amplitudes, intervals, and diagnostic statements.15,16 computer era have appeared during the past several decades. For these reasons, the AHA initiated an updating of The most recent comprehensive AHA recommendations for

by guest on October 18, 2017 guideline statements for standardization and interpretation of the standardization of leads and general technical require- the ECG. The project has been endorsed by the American ments of ECG instruments were published in 1975.5 In 1978, College of Cardiology, the Heart Rhythm Society, and the task forces of the American College of Cardiology produced International Society for Computerized Electrocardiology. a collection of reports on optimal electrocardiography,7 which The purposes of this project are as follows: (1) to review the addressed standardization of terminology and interpreta- status of techniques currently used to record and interpret the tion,13 the development of databases,6 the quality of ECG ECG and to identify opportunities for modification; (2) to records,12 computers in diagnostic cardiology,9 the use of simplify and unify the various descriptive, diagnostic, and ECGs in practice,10 cost-effectiveness of the ECG,11 and a modifying terminologies currently used in order to create a discussion of future directions.14 In Europe, international common and more easily applied lexicon; and (3) to identify common standards for quantitative electrocardiography the weaknesses of the descriptive, interpretative, and com- (CSE) evolved from the work of Willems and colleagues.19–22 parative algorithms and recommend changes that incorporate The CSE studies were designed to reduce the wide variation the newly recognized factors referred to above. in wave measurements obtained by ECG computer programs The chairman (L.S.G.) was selected by the Electrocardiog- and to assess and improve the diagnostic classification of raphy and Arrhythmias Committee of the Council on Clinical ECG interpretation programs.22 Given the expanding use of Cardiology of the AHA. He formed an advisory group to computer-based ECG systems and evolving technology, rec- assist in setting goals and to recommend other writing group ommendations for bandwidth and digital signal processing members. The committee met on 5 occasions to discuss goals, standards during automated electrocardiography were formu- identify specific areas that required updating, and review lated in 1990 by a committee of the AHA.23 In 1991, progress. A smaller working/writing group with a group recommendations of the 1975 and 1990 AHA documents leader was chosen for each topic. This is the first of 6 articles were incorporated into a summary document on diagnostic written in response to the AHA mandate. It is followed by a ECG devices that was developed by the Association for the glossary of descriptive, diagnostic, and comparative state- Advancement of Medical Instrumentation (AAMI) and ap- ments that attempts to minimize repetitive and noninforma- proved by the American National Standards Institute tive statements. Additional articles, to be published subse- (ANSI).24 This document was reaffirmed by ANSI in 2001. quently, will discuss the ECG interpretation of intraventricular Other statements have addressed related issues of ECG conduction disturbances, abnormalities of ventricular repolariza- utilization and physician competence in interpretation of the tion, hypertrophy, and /infarction. ECG.16,18,25–27 1308 Circulation March 13, 2007

The ECG Signal and Its Processing the heart. Simultaneously active wave fronts within the heart Automated analysis of the digital 12-lead ECG involves may confound the seeming simplicity of these models. signal analysis and diagnostic classification.28 Processing of The fundamental frequency for the QRS complex at the the ECG occurs in a series of steps, each of which requires body surface is Ϸ10 Hz, and most of the diagnostic informa- adherence to methodological standards. These steps include tion is contained below 100 Hz in adults, although low- (1) signal acquisition, including filtering; (2) data transfor- amplitude, high-frequency components as high as 500 Hz mation, or preparation of data for further processing, includ- have been detected and studied. The QRS of infants often ing finding the complexes, classification of the complexes contains important components as high as 250 Hz.35 The into “dominant” and “nondominant” (ectopic) types, and fundamental frequency of T waves is approximately 1 to 2 formation of an average or median complex for each lead; (3) Hz.23 Filtering of the ECG signal to within the band between waveform recognition, which is the process for identification 1 to 30 Hz produces a stable ECG that is generally free of of the onset and offset of the diagnostic waves; (4) feature artifact, but this bandwidth is unacceptable for diagnostic extraction, which is the measurement of amplitudes and recording because it produces distortions of both high- and intervals; and (5) diagnostic classification. Diagnostic classi- low-frequency components of the signal. The high-frequency fication may be heuristic (ie, deterministic, or based on components of the ECG signal define the most rapidly experience-based rules) or statistical in approach.29 changing parts of the signal, including Q waves and notched components within the QRS complex. Because QRS ampli- The ECG Signal tude measurement depends on accurate detection of the peak Downloaded from The standard 12-lead ECG records potential differences of an R wave, an inadequate high-frequency response results between prescribed sites on the body surface that vary during in systematic underestimation of signal amplitude and in the cardiac cycle; it reflects differences in transmembrane smoothing of notches and Q waves. On the other hand, an voltages in myocardial cells that occur during depolarization inadequate low-frequency response can result in important and repolarization within each cycle. The ECG was regarded distortions of repolarization. Accordingly, the transfer func- http://circ.ahajournals.org/ by Einthoven et al30 as originating in a stationary, time- tions of the filtering algorithms of analog and digital electro- dependent single-dipole source that can be represented by a cardiographs have a major effect on the resulting ECG. vector, the heart vector. In this model, voltage in any lead was explained by projection of the heart vector onto the straight ECG Signal Processing line that defined the lead axis. Burger et al31,32 expanded this Processing of the ECG signal by a digital electrocardiograph concept by treating the lead axes as vectors. A lead vector, in involves initial sampling of the signal from electrodes on the addition to having a direction that is not the same as that of body surface. Next, the digital ECG must eliminate or

by guest on October 18, 2017 the lead axis, also has a length. Voltage in a lead is not merely suppress low-frequency noise that results from baseline the projection of the heart vector on the lead axis but also its wander, movement, and respiration and higher-frequency projection on the lead vector times the length (ie, the noise that results from muscle artifact and power-line or “strength”) of the lead vector. Direction and strength of a lead radiated electromagnetic interference.36 As a result, the ECG vector depend on the geometry of the body and on the varying signal at the body surface must be filtered and amplified by electric impedances of the tissues in the torso.31,32 Pairs of the electrocardiograph. Digital filters can be designed to have electrodes (or a combination of electrodes serving as 1 of the linear phase characteristics, and this avoids some of the 2 electrodes) and the tracings that result from their use are distortion introduced by classic analog filters. Once filtered, known as leads. Placement of electrodes on the torso is individual templates are constructed for each lead from data distinct from direct placement on the heart, because the sampled generally from dominant complexes, from which localized signal strength that occurs with direct electrode amplitude and duration measurements are made. Global contact is markedly attenuated and altered by torso inhomo- measurements are made from individual lead data or from geneities that include thoracic tissue boundaries and varia- mathematical combinations of simultaneously acquired indi- tions in impedance. At any point in time, the electrical vidual lead data. Measurement error has an important effect activity of the heart is composed of differently directed on the accuracy of ECG diagnostic statements.37 Reference is forces. Accordingly, the potential at any point on the body made to the comprehensive analysis of technical factors that surface represents the instantaneous uncanceled electrical affect the ECG by Zywietz.38 In the present statement, factors forces of the heart, where cancellation also is dependent on that affect the processing of the ECG signal will be discussed torso inhomogeneities. For further reading, see the compre- in terms of technology, clinical implications, and hensive analysis of lead theory by Horacek in 1989.33 As recommendations. electrodes move farther away from the heart, signal strength decreases together with lead strength. According to solid Sampling of the ECG Signal angle theory, signal magnitude can be related to both spatial Technology and nonspatial factors.34 Nonspatial factors include the mag- Direct-writing electrocardiographs, which were preponderant nitude of transmembrane potential difference across a bound- until the 1970s, recorded signals that were analog, that is, ary within the heart. Spatial factors include the projected continuous, in nature. Nearly all current-generation ECG boundary of the difference in potential relative to the area of machines convert the analog ECG signal to digital form a sphere of unit size; this will increase with the absolute size before further processing. Analog-to-digital conversion in of the area but decrease with distance of the electrode from modern digital ECGs generally occurs at the front end, such Kligfield et al Standardization and Interpretation of the ECG, Part I 1309

as the lead cable module. The initial sampling rate during introduces considerable distortion into the ECG, particularly analog-to-digital conversion at the front end is higher than the with respect to the level of the ST segment.39,40 This distor- sampling rate that is used for further processing of the ECG tion results from phase nonlinearities that occur in areas of the signal. Oversampling was originally introduced to detect and ECG signal where frequency content and wave amplitude represent pacemaker stimulus outputs, which are generally change abruptly, as occurs where the end of the QRS complex Ͻ0.5 ms in duration. Front-end sampling has been performed meets the ST segment. Digital filtering provides methods for at rates from 1000 to 2000 per second, but newer converters increasing the low-frequency cutoff without the introduction can routinely sample at 10 000 to 15 000 per second or even of phase distortion.23 This can be accomplished with a higher; other converters are adaptive in sampling rate, with bidirectional filter by a second filtering pass that is applied in output that is proportional to the energy detected. reverse time,41 that is, from the end of the to the onset of the P wave. This approach can be applied to ECG signals Clinical Implications that are stored in computer memory, but it is not possible to The initial sampling rate used by the computer to transform achieve continuous real-time monitoring without a time lag. the analog electrical signal to a series of discrete digital points Alternatively, a zero phase shift can be achieved with a flat (generally described in the unit of samples per second, or step response filter,42 which allows the reduction of baseline imprecisely as a sampling rate of x Hz) is most often many drift without low-frequency distortion. times greater than required for further processing of the ECG signal. This is known as “oversampling.” Pacemaker stimulus Clinical Implications

Downloaded from outputs are generally shorter in duration than 0.5 ms, and Low-frequency noise, such as that produced by respiration, therefore, they cannot be reliably detected by ordinary signal causes the tracing to wander above and below the baseline. A processing technique at 500 to 1000 Hz. Accordingly, a low-frequency cutoff at 0.5 Hz, which was once widely used primary benefit of oversampling is the detection of narrow in ECG rhythm monitors, reduces baseline drift due to the pacemaker pulses. Pacemaker detection is not reliably or generally lower frequency of respiratory motion but can

http://circ.ahajournals.org/ accurately performed in all current systems. Oversampling result in marked distortion of repolarization that may produce can also improve signal quality at the high-frequency cutoff. artifactual ST-segment deviation.39 The 1975 AHA recom- Separate from difficulties caused by pacemaker spike dura- mendations included a 0.05-Hz low-frequency cutoff for tion, the very small amplitudes of modern bipolar pacemaker diagnostic electrocardiography.5 This recommendation pre- stimulus outputs are often too small to be recognized on the serves the fidelity of repolarization, but it does not eliminate standard ECG, a problem that requires resolution without the problem of baseline drift. Baseline drift suppression is introducing artificially enhanced pacemaker signals into the necessary for coherent alignment of the sequential complexes tracing. that many modern ECG systems use in the formation of a by guest on October 18, 2017 representative PQRST complex, which is sometimes called a Recommendations template; otherwise, baseline wander can distort template Oversampling by a significant multiple of the upper- amplitudes. Newer digital filters can correct baseline drift frequency cutoff is recommended to provide recommended while preserving the fidelity of ST-segment levels, and these bandwidth in the digitized signal. Manufacturers should digital methods obligate revision of prior standards required continue to develop improved algorithms for the identifica- for analog filters. tion and quantitative presentation of pacemaker stimulus outputs and for their preservation during ECG storage and Recommendation retrieval. Low-amplitude pacemaker stimulus outputs should To reduce artifactual distortion of the ST segment, the 1990 not be artificially increased in amplitude to aid recognition, AHA document recommended that the low-frequency cutoff because this would distort the form of the recorded ECG. be 0.05 Hz for routine filters but that this requirement could Instead, it is recommended that manufacturers incorporate a be relaxed to 0.67 Hz or below for linear digital filters with separate representation of detected pacemaker stimulus out- zero phase distortion.23 The ANSI/AAMI recommendations puts into 1 row only of the standard output tracing that would of 1991, affirmed in 2001, endorsed these relaxed limits for aid the identification of atrial, ventricular, and biventricular low-frequency cutoff for standard 12-lead ECGs, subject to pacing signals. The selected row might be a rhythm strip that maximum allowable errors for individual determinants of accompanies the standard 3 rows of lead signals in 4 columns, overall input signal reproduction.24 These standards continue or in the absence of a rhythm row, 1 of the standard rows to be recommended. might be selected for this purpose. High-Frequency Filtering Low-Frequency Filtering Technology Technology The digital sampling rate (samples per second) determines the The heart rate, in beats (cycles) per minute (bpm), when upper limit of the signal frequency that can be faithfully divided by 60 (seconds per minute) forms a lower bound for represented. According to the Nyquist theorem, digital sam- the frequency content in Hertz (Hz, cycles per second). In pling must be performed at twice the rate of the desired practice, this is unlikely to be lower than 0.5 Hz, which high-frequency cutoff. Because this theorem is valid only for corresponds to a heart rate of 30 bpm; heart rates below 40 an infinite sampling interval, the 1990 AHA report recom- bpm (0.67 Hz) are uncommon in practice.23 However, with mended sampling rates at 2 or 3 times the theoretical traditional analog filtering, a 0.5-Hz low-frequency cutoff minimum.23 A series of studies have now indicated that data 1310 Circulation March 13, 2007

at 500 samples per second are needed to allow the 150-Hz between beats. Accordingly, the ANSI/AAMI standards rec- high-frequency digital filter cutoff that is required to reduce ommend using the largest-amplitude deflection in each lead amplitude error measurements to Ϸ1% in adults.43,44 Greater as representative of the magnitude for that measurement.24 bandwidth may be required for accurate determination of Measurements from digitized records are more reproducible amplitudes in infants.35,45,46 The European CSE group recom- than those from analog tracings.53 Digital electrocardiographs mended that waveforms should be recognized if they have can reduce or eliminate unwanted beat-to-beat variations amplitudes of at least 20 ␮V and durations of at least 6 ms.23 within leads by forming “templates” for individual leads that This implies a high-frequency response in the range of 150 serve as representative complexes. Willems et al54 have Hz. A 2001 Dutch report showed that in order to keep shown that programs that analyzed an averaged beat showed amplitude errors Ͻ25 ␮VinϾ95% of the cases, a bandwidth significantly less variability than programs that measured up to 250 Hz is needed for pediatric cases and up to 150 Hz every complex or a selected beat; similar findings have been for adolescents.35 reported by Zywietz and colleagues.55 Single-lead average or median-complex templates may be derived from selected, Clinical Implications The higher the frequencies contained in the filtered signal, the accurately aligned complexes. One algorithm combines tech- more accurate will be the measurement of rapid upstroke niques to use the median values of several averaged cycles. velocity, peak amplitude, and waves of small duration.44 Methods vary for the accurate alignment of normal PQRST Inadequate high-frequency response reduces the amplitude of complexes for these purposes but generally involve template

Downloaded from QRS measurements and the ability to detect small deflections. matching and cross-correlation algorithms that exclude non- Because digital ECGs have a temporal resolution in millisec- dominant waveforms. Alignment is critical to the success of onds and an amplitude resolution in microvolts, recommen- the measurement process that follows template formation. dations for the high-frequency response of ECGs have Noise, measured as RMS (root mean square) residual error in evolved over the years. A high-frequency cutoff of 100 Hz aligned representative complexes, can affect measurements of duration and compromise the tradeoff between sensitivity and http://circ.ahajournals.org/ was considered adequate by the AHA in 1975 to maintain diagnostic accuracy during visual inspection of direct-writing specificity for infarction criteria, among other diagnoses.56 tracings by electrocardiographers.5 Even so, it has long been Residual error is reduced by incorporation of more complexes recognized that higher-frequency components of the QRS into the representative complex. Zywietz43 has demonstrated complex are present47,48 and that these components may have that noise levels in constructed complexes can be reduced to clinical significance in patients with various forms of heart below 5 ␮V to allow deflections of 20 ␮V to be estimated disease.49–51 To measure routine durations and amplitudes with no more than 10% error. However, not all variability accurately in adults, adolescents, and children, an upper- between complexes is due to noise, and a study using the CSE by guest on October 18, 2017 frequency cutoff of at least 150 Hz is required; an upper- database has suggested that the diagnostic value of a repre- frequency cutoff of 250 Hz is more appropriate for infants. sentative complex may be improved under some circum- An obvious consequence of these high-frequency recommen- stances by consideration of the classification of individual dations is that reduction of noise by setting the high- complexes.57 Although fidelity standards for other ECG frequency cutoff of a standard or monitoring ECG to 40 Hz features are contained in the 1990 AHA document,23 no will invalidate any amplitude measurements used for diag- fidelity standard exists for accuracy of representative beat nostic classification.52 construction. Recommendations Clinical Implications The ANSI/AAMI standard of 1991, reaffirmed in 2001, Some biological beat-to-beat variation undoubtedly exists in recommended a high-frequency cutoff of at least 150 Hz for the electrical activity of the heart, separate from respiratory all standard 12-lead ECGs.24 The ANSI/AAMI document also variability, which is recorded in the surface ECG. For special details maximum allowable errors for individual determinants purposes, such as the detection of QRS and T-wave alternans, of overall input signal reproduction, which extend beyond the it may be desirable to retain the ability to examine these scope of the present report but are important guidelines for beat-to-beat changes. For routine recording of the ECG, manufacturers.24 These most recent limits continue to be however, reduction of noise by formation of a single and recommended for adolescents and for adults, with extension stable representative complex for analysis of each lead results of the high-frequency cutoff to 250 Hz in children,35 subject from exclusion of cycle-to-cycle change. Digital electrocar- to demonstration of fidelity testing by individual manufactur- diographs can adjust for respiratory variability and decrease ers according to standard methods.23 Electrocardiographs beat-to-beat noise to improve the measurement precision in should automatically alert the user when a suboptimal high- individual leads by forming a representative complex for each frequency cutoff, such as 40 Hz, is used, and a proper lead. Automated measurements are made from these repre- high-frequency cutoff should automatically be restored be- sentative templates, not from measurement of individual tween routine standard ECG recordings. complexes. Average complex templates are formed from the average amplitude of each digital sampling point for selected Formation of a Representative Single-Lead Complex complexes. Median complex templates are formed from the Technology median amplitude at each digital sampling point. As a result, QRS waveform amplitudes and durations are subject to measurement accuracy is strongly dependent on the fidelity intrinsic beat-to-beat variability and to respiratory variability with which representative templates are formed. Kligfield et al Standardization and Interpretation of the ECG, Part I 1311

Recommendations dispersion that results from isoelectric components of the T Digital electrocardiographs must provide beat alignment that wave in some leads of the normal ECG.60,61 allows selective averaging or formation of a representative Measurement from simultaneous leads provides a method complex with fidelity adequate for diagnostic ECG computer for identification of the earliest onset and latest offset of programs. Fidelity standards for construction of representa- waves that are used for duration measurements. Waveform tive complexes need to be developed. measurements taken from temporally aligned lead informa- tion will be systematically greater than the corresponding Global Measurement From Simultaneously measurements made from single leads or measurements Acquired Leads averaged from several leads. P-wave and PR-interval dura- tions, QRS duration, and QT interval in population studies Technology will be greater when measured from temporally aligned Some, but not all, digital electrocardiographs utilize the time multiple leads or from a spatial vector lead template than coherence of simultaneously acquired representative com- when measured from individual leads. In addition, global plexes to derive “global” measurements of intervals. Tempo- measurement can affect Q-wave durations that determine the ral superposition of complexes permits the earliest onset and ECG diagnosis of . Accordingly, redef- latest offset of waveforms to be identified for measurement of inition is required of population-based criteria for first-degree intervals that are more accurate than can be obtained from , P-wave duration, Q-wave duration in single leads. This can be done by searching for the earliest

Downloaded from infarction (relative to the earliest onset of the QRS complex), and latest time points of rapid voltage change across tempo- QRS duration, and QT intervals measured from simultaneous rally aligned individual complexes. Alternatively, a spatial lead technology. Several studies of normal limits of ECG vector magnitude may be created for multiple leads, as measurements derived from simultaneously recorded 12-lead exemplified for 3 leads by (x2ϩy2ϩz2)1/2, and fiducial points ECGs have already been published.62–66 Global measurement may be determined from this magnitude function. An equally of the QT interval is desirable for routine electrocardiogra- http://circ.ahajournals.org/ useful function can be derived as |⌬x|ϩ|⌬y|ϩ|⌬z|, where ⌬x is phy, but global QT measurement remains problematic even the amplitude difference between 2 consecutive samples in when derived from temporally aligned complexes. This is due lead x, etc, which is a spatial velocity function. When only in part to differences in the currently available algorithms that several selected representative complexes are included in the are used to define and to identify the end of the T wave, global measurement, intervals may still be underestimated if which can affect measurements.59 Until reproducible meth- earliest onset and latest offset times are not detected. Con- odology is established in this area, comparative analyses of versely, global measurements may overstate intervals by ECGs must recognize the potential effect of different algo-

by guest on October 18, 2017 inclusion of single-lead information that would not be visu- rithms on resulting simultaneous lead measurements. Special ally accepted by a human overreader. Differences in mea- situations, such as QT monitoring in drug trials, may continue surements may also result from differences in the method of to require alternative methods of QT measurement from lead alignment or template formation and from differences in single or multiple leads. definition of waveform onset and offset by different algo- rithms of different manufacturers. The importance of this Recommendations phenomenon is seen in determination of the QT interval, Global measurements of intervals should be obtained from where different approaches to definition of T-wave offset can time-coherent data in multiple leads to detect the earliest confound reproducibility.58,59 It is in this context that differ- onset and latest offset of waveforms. For routine purposes, ences in ECG measurement performance of different global measurements of P-wave duration, PR interval, QRS computer-assisted analysis programs must be placed.15,17 duration, and QT duration should be stated on the ECG report. A comparative study is needed of global measure- Clinical Implications ments made by different methods from a reference standard. The capability for simultaneous 12-lead data acquisition by Differences in global measurement algorithms and methods modern digital electrocardiographs obligates major reconsid- should be minimized to promote standardization, but these eration of measurement standards and reference values for differences must be accounted for in comparative studies intervals that were originally derived from analog, single- within individuals and between individuals. Attention must channel recordings. When the vector orientation of any lead is be paid to definition of normal ECG ranges in children and approximately perpendicular to the heart vector during the adolescents, as well as in adults, with stratification for initial or terminal portion of an ECG waveform, an isoelectric specific age groups, sex, and race. Where methods vary, component of the initial or terminal component of the algorithm-specific normal ranges for intervals need to be waveform will be recorded in that lead at that time. Because derived. With respect to QT interval, the end of the T wave as there can be no accurate time alignment of leads in single- determined globally should match with a well-defined channel recordings, duration measurements from individual T-wave offset in at least 1 of its component individual leads. leads will in most cases fail to detect the earliest onset or the Alternative methods of QT measurement from single or latest offset of waveforms. As a result, measurements from multiple leads may be prescribed for special purposes such as single leads will systematically underestimate durations of drug evaluation, but it is inappropriate for studies involving components of the PQRST complex.21 Simple demonstration serial comparison of the QT interval to use differing methods of this phenomenon is seen in the measurement of QT of QT measurement within trials. 1312 Circulation March 13, 2007

Data Compression for Transmission, Storage, and signal,23,73 and they can be eliminated with newer methods of Retrieval of ECGs lossless compression (in which no loss of ECG data occurs). Technology Recommendation Digitized at 500 samples per second, 10 seconds of a single Compression algorithms should perform in a manner that lead of ECG record requires Ϸ10 kB of memory. Accord- allows retrieved data to adhere to the fidelity standards ingly, 10 seconds of an uncompressed 12-lead ECG digitized established in the 1990 AHA statement with reference to the at recommended standards would occupy about 80 to 100 Kb original signal. of memory, in addition to memory needed for template complexes and demographic data. Several methods of ECG Standard Leads data compression have been used to reduce processing time Location of Standard Limb and Precordial Electrodes and to minimize the memory required for permanent data storage.67,68 Techniques include fast Fourier, discrete cosine, Technology The standard 12-lead ECG5,24 consists of 3 limb leads (leads and wavelet transforms, as well as hybrid compression I, II, and III), 3 augmented limb leads in which the Gold- methods.69–73 These methods can provide compression ratios berger modification of the central terminal of Wilson serves of 8:1 to 10:1 with resulting root mean square errors that as a derived indifferent electrode that is paired with the range from Ͻ0.5% to Ͼ2%.69,70,74 Compression ratio is exploring electrode (leads aVR, aVL, and aVF), and 6 generally inversely related to root mean square error, so that

Downloaded from precordial leads in which the Wilson central terminal serves a recent algorithm was able to provide a 20:1 compression as a derived indifferent electrode that is paired with the ratio but with a root mean square error of 4%.70 Because exploring electrode (V through V ). All leads are effectively compression affects high-frequency components of the ECG 1 6 “bipolar,” and the term “unipolar” in description of the to a greater extent than low-frequency components, at least 1 augmented limb leads and the precordial leads lacks preci- algorithm has used bimodal decimation of the signal in which sion. Reference is made to the comprehensive study of lead http://circ.ahajournals.org/ QRS complexes are kept at 500 samples per second while the systems for various types of electrocardiography by Macfar- rest of the recording is compressed to lower sampling rates.75 lane.77 Skin preparation by cleaning and gentle abrasion Compression of data may occur before or after signal pro- before electrode application can reduce noise and improve the cessing, but in either case, compression occurs before transfer quality of the recorded ECG.78–80 Historically, limb lead of the signal to central storage systems and affects all electrodes have been attached at the wrists and the ankles, retrieved records. Accordingly, the 1990 AHA report recom- with the patient in the supine position, generally with a pillow mended that the fidelity of retrieved compressed data should under the head. For routine 12-lead recording, the AHA 23 by guest on October 18, 2017 ␮ be within 10 V for corresponding samples. As computer statement of 1975 recommended placement of the 4 limb lead networks increase transmission speed and storage capacity, electrodes on the arms and legs distal to the shoulders and lossless compression techniques may supersede other com- hips,5,81 and thus not necessarily on the wrists and ankles. pression methods for some applications. Evidence exists that different placement of electrodes on the Clinical Implications limbs can alter the ECG, a phenomenon that appears to be Compression of ECG data can speed transmission and re- more marked with respect to the left arm electrode.81 There- trieval of records that are stored in central databases and fore, reevaluation of the magnitude of changes due to varia- minimize memory required for storage. Algorithms based on tion in limb electrode placement in clinical practice is a variety of mathematical transforms can compress data by a required, as discussed below. Six electrodes are placed on the factor of Ϸ8, with signal fidelity preserved within about a 2% chest in the following locations: V1, fourth intercostal space at overall error. However, the error may not be uniform the right sternal border; V2, fourth intercostal space at the left throughout the ECG cycle. Data compression affects high- sternal border; V3, midway between V2 and V4;V4, fifth frequency (short duration) signals more than the smoother intercostal space in the midclavicular line; V5, in the horizon- low-frequency signal. Therefore, compression has greater tal plane of V4 at the anterior axillary line, or if the anterior potential to alter measurements within the QRS complex, axillary line is ambiguous, midway between V4 and V6; and such as pacemaker spikes, Q-wave duration, and R-wave V6, in the horizontal plane of V4 at the midaxillary line. amplitude, than to alter other signals such as the ST segment Clinical Implications and the T wave. In some cases, a noncompressed ECG taken Skin preparation and electrode placement have important at the bedside may differ from the tracing later retrieved from effects on the ECG, and patient positional change, such as the stored, compressed file, which may also affect serial elevation and rotation, can change recorded amplitudes and comparison of original and retrieved tracings when ECG axes. It has been widely accepted for many years that ECG waveforms are reanalyzed.76 Furthermore, differences in amplitudes, durations, and axes are independent of the distal compression methodology may affect comparison of re- or more proximal location of the limb electrodes. As a result, trieved tracings from different manufacturers in the same way routine recording of the ECG from the upper arm rather than that different filters and different use of time-coherent tem- from the wrist to “reduce motion artifact” has become plates affect measurements of the ECG signal. These differ- popular and is facilitated by the development of disposable ences will be minimal when compressed tracings adhere to tab electrodes. However, one study has shown that electrode established or newer standards of fidelity to the original placement along the limbs can affect ECG voltages and Kligfield et al Standardization and Interpretation of the ECG, Part I 1313

durations, most importantly in the limb leads.81 Whether ECGs will depend greatly on the care with which electrodes these differences are large enough to alter routine diagnostic are ordinarily placed and also on breast size, breast shape, and criteria, such as voltage for left or small changes in patient position. Similar considerations Q-wave duration for inferior infarction, is unknown. Further apply in relation to subjects with breast implants and in confounding this situation is the variability in electrode subjects who are obese. placement that might have been present during the actual derivation of the diagnostic criteria involved, because studies Recommendations during the past several decades have rarely described elec- Technicians and other medical personnel responsible for the trode placement in detail. recording of ECGs should have periodic retraining in skin From the time of their initial standardization by a joint preparation, proper electrode positioning, and proper patient committee of the AHA and the Cardiac Society of Great positioning. All leads are effectively “bipolar,” and the Britain and Ireland,82,83 the normal precordial electrode posi- differentiation between “bipolar” and “unipolar” in the de- tions have been relatively horizontal in orientation. When scription of the standard limb leads, the augmented limb precordial electrodes are positioned without reference to the leads, and the precordial leads is discouraged. Neither term underlying bony landmarks, the placement pattern often is should be used. Studies to clarify the effect of distal versus erroneously vertical in orientation.84 Mapping data document proximal limb lead electrode placement on ECG magnitudes the often profound alterations in waveforms that can result and durations are required. Validity of test performance from precordial electrode misplacement.85,86 A common error criteria for current diagnostic algorithms may be dependent Downloaded from

is superior misplacement of V1 and V2 in the second or third on placement of limb leads in the same positions that were intercostal space. This can result in reduction of initial used for criteria development. Pending resolution of this R-wave amplitude in these leads, approximating 0.1 mV per issue, all ongoing studies used for criteria development must interspace, which can cause poor R-wave progression or clearly document electrode placement with precision. The 87 erroneous signs of anterior infarction. Superior displace- horizontal plane through V4 is preferable to the fifth intercos- http://circ.ahajournals.org/ Ј ment of the V1 and V2 electrodes will often result in rSr tal interspace for the placement of V5 and V6 and should be

complexes with T-wave inversion, resembling the complex in used for placement of these electrodes. Definition of V5 as

lead aVR. It also has been shown that in patients with low midway between V4 and V6 is conducive to greater reproduc- diaphragm position, as in obstructive pulmonary disease,88,89 ibility than occurs for the anterior axillary line, and this V3 and V4 may be located above the ventricular boundaries should be used when the anterior axillary line is not well

and record negative deflections that simulate anterior infarc- defined. In the placement of V6, attention should be directed tion. Another common error is inferior placement of V5 and to the definition of the midaxillary line as extending along the by guest on October 18, 2017 V6, in the sixth intercostal space or even lower, which can middle, or central plane, of the thorax. For the time being, it alter amplitudes used in the diagnosis of ventricular hyper- is recommended that electrodes continue to be placed under trophy. Precordial lead misplacement explains a considerable the breast in women until additional studies using electrodes amount of the variability of amplitude measurements that is placed on top of the breast are available. found between serial tracings.90 Some residual disagreement persists in current guidelines and texts on the standard for Derivation of the Standard Limb Leads and location of V5 and V6, with some sources retaining an early Relationships Among Leads recommendation that these leads follow the course of the fifth Technology intercostal space rather than the horizontal plane of V4.In addition, it is common to refer to the anterior axillary line as The 4 limb electrodes define the standard frontal plane limb leads that were originally defined by Einthoven. With the an anatomic marker for the placement of V5. These alterna- tives are discouraged because the course of the intercostal right leg electrode acting as an electronic reference that serves space is variable and the definition of an anterior axillary line to improve common mode (unwanted noise) rejection, 3 pairs only vague. Placement of precordial electrodes in women of electrodes exist. Within each pair, 1 electrode is estab- with large breasts remains problematic. Electrodes are most lished as the positive end of the lead in the sense that current commonly placed beneath the breast, which should reduce flow toward that electrode is inscribed in an upward (posi- amplitude attenuation caused by the higher torso impedance tive) direction. The other electrode of the pair would inscribe in women and, intuitively, would seem to favor reproducibil- the exactly opposite waveform. Lead I is defined as the ity of positioning during routine practice. Conversely, one potential difference between the left arm and the right arm study has suggested that reproducibility of ECG measure- (LA-RA), lead II is defined as the potential difference ments is slightly increased when electrodes are positioned on between the left leg and the right arm (LL-RA), and lead III top of the breast.91 Another study using precisely ascertained is defined as the potential difference between the left leg and electrode placement has suggested that precordial potential the left arm (LL-LA). In each case, net current flow toward attenuation by the breast is very small.92 Yet another study the first electrode of the pair is defined as a positive voltage

has found attenuation only in V3 and an increase in voltage in deflection in the recorded waveform. According to Kirch- 93 V5 and V6 when electrodes are placed over the breast; this hoff’s law, the sum of the voltage gains and voltage drops in ϭ may result from V5 and V6 being correctly placed at the level a closed circuit is equal to zero. Therefore, lead II lead ϩ of V4 rather than more inferiorly when V4 is positioned under I lead III at any instant in the cardiac cycle. This relationship the breast. Clearly, the magnitude of this effect in ordinary is known as Einthoven’s law. 1314 Circulation March 13, 2007

Clinical Implications terminals for the augmented limb leads are now obtained as From 3 pairs of limb electrodes, 6 waveforms may be (LAϩLL)/2 for aVR, (RAϩLL)/2 for aVL, and (RAϩLA)/2 obtained, 3 of which are defined as the standard limb leads by for aVF. Lead aVL therefore represents the potential differ- establishing 1 of each pair as the electrode toward which net ence between the left arm and the modified terminal of current flow will inscribe an upward (positive) voltage Goldberger and is given by LAϪ(RAϩLL)/2, which can be deflection on the ECG. The opposite waveforms, by defini- reduced to (lead IϪlead III)/2. Similarly, lead aVR is tion, are mirror images of the standard limb leads. In this RAϪ(LAϩLL)/2, which can be reduced to Ϫ(lead Iϩlead sense, the electrical activity defined by a lead pair can be II)/2, and lead aVF is LLϪ(LAϩRA)/2, which can be examined from either perspective. Distinction of single elec- reduced to (lead IIϩlead III)/2. These derived leads provide trodes from established “poles” is highlighted by selection of new vectorial perspective within the frontal plane. It should the LA electrode as the positive end of the LA-RA pair for be noted that aVRϩaVLϩaVFϭ0 at any point in the cardiac lead I but not as the positive end of the LL-LA pair for lead cycle. The 6 standard precordial leads are based on potential III. Einthoven’s law indicates that any 1 of the standard limb differences between an exploring electrode on the chest wall leads can be mathematically derived from the other 2 leads. and the original WCT. Each precordial lead, symbolized as As a consequence, the 3 standard limb leads contain only 2 Vi, represents the potential difference given by ViϪWCT. independent pieces of information. Even though limb lead placement is often represented in terms of the apices of an Clinical Implications equilateral triangle, known as the Einthoven triangle, The augmented limb leads and the precordial leads use a Downloaded from Einthoven’s law is entirely independent of any assumptions derived electrode to serve as the opposing electrode of the about geometric placement of the 3 electrodes. These consid- lead pair. Wilson made a reasonable assumption that the erations notwithstanding, redundant leads promote the appre- potential oscillations of his central terminal would be small ciation of spatial morphological characteristics of the ECG compared with those of the exploring electrode and that his and aid in its interpretation, such as calculation of axis, and “unipolar” leads therefore would largely reflect the potential http://circ.ahajournals.org/ consideration of the information from the perspective of both variation under the exploring electrode. Later investigators ends of the available leads can be clinically useful, particu- have often mistakenly taken this to mean that these leads larly in the evaluation of ST-segment shifts during acute reflect electrical activity only of cardiac regions in the myocardial infarction. vicinity of the exploring electrode. This fails to recognize that the potential at the exploring electrode is determined by all Recommendation cardiac sources electrically active at a given instant of cardiac Users should recognize the redundancy of information in the excitation and repolarization cycle. Even though the aug-

by guest on October 18, 2017 standard limb leads. Redundancy notwithstanding, the infor- mation contained in different perspectives from multiple mented limb leads provide vectorial insight within the frontal leads can be used to improve recognition of ECG plane, each of these leads can also be mathematically derived abnormalities. from any 2 of the standard limb leads, as demonstrated above; accordingly, they do not contain new information but rather Derivation of the Augmented Limb Leads and the provide new views of cardiac electrical activity. This calcu- Precordial Leads lation is mathematically independent of any assumption about the equilateral nature of the Einthoven triangle. As a conse- Technology An electrode potential can also be obtained as an average (or quence, the 6 frontal plane leads, consisting of the 3 standard weighted average) of the potentials at 2 or more body surface limb leads and the 3 augmented limb leads, actually contain locations, which creates a potential that is different from each only 2 independent measured signals. In practice, modern of the contributing electrodes alone. Wilson and colleagues94 electrocardiographs measure potential differences for 2 pairs devised a central terminal based on the limb electrodes to of limb lead electrodes and use these measurements to serve as a new reference potential. The Wilson central mathematically derive the third standard limb lead and each terminal (WCT) is obtained as an average potential of the RA, of the augmented limb leads. Although redundancy exists LA, and LL electrodes, so that the potential at within the 6 frontal plane leads, visualization of multiple WCTϭ(RAϩLAϩLL)/3. Kirchhoff’s law does not require leads promotes appreciation of spatial aspects of the ECG that that the potential at WCT be zero or that it remain constant can be important to clinical interpretation. Unlike the math- throughout the cardiac cycle. Potential differences between ematical relationships between the frontal plane limb leads, WCT and RA, LA, and LL, respectively, defined new frontal each of the precordial electrodes provides uniquely measured plane limb leads VR, VL, and VF. Wilson called these potential differences at the recording site with reference to the electrode pairs the “unipolar” limb leads. Wilson’s VR, VL, central terminal. Because the exploring precordial electrodes and VF leads had relatively low amplitudes because the are not connected in a closed electrical loop like the extremity potential at the exploring site was also included in the central electrodes, the precordial leads are independent of each other; terminal. By removing the single exploring potential from the none can be calculated precisely from other information in central terminal, Goldberger produced the “augmented unipo- the ECG. Therefore, the “standard” 12-lead ECG actually lar” limb leads, so-called because they mathematically are contains 8 independent pieces of information: 2 measured 50% larger in amplitude with respect to recordings that use potential differences from which the 4 remaining limb leads the Wilson central terminal.95,96 The Goldberger central can be calculated and the 6 independent precordial leads. Kligfield et al Standardization and Interpretation of the ECG, Part I 1315

Recommendations and sequentially in the same way that the precordial leads 100,101 The augmented limb leads of the frontal plane and the progress sequentially from V1 through V6. With inverted precordial leads result from derived electrode pairs and aVR (ϪaVR or maVR) used to represent the signal between should not be described as “unipolar.” Users should recognize leads II and I, the sequence becomes, from right to left, III, the derived and redundant nature of the 3 augmented limb aVF, II, ϪaVR, I, and aVL, or from left to right, aVL, I, leads, but these are retained because multiple leads facilitate ϪaVR, II, aVF, and III. In addition to improved spatial the clinical interpretation of the ECG. quantification of acute infarction, the Cabrera sequence facilitates calculation of the frontal plane axis.102 This pre- Simultaneous Lead Presentation sentation, when in sequence with the precordial leads, has Technology also been termed the panoramic display.103 With analog single-channel ECG recorders, each lead is recorded sequentially by means of a switching mechanism Clinical Implications that connects applied electrodes in the prescribed combina- Whether presented serially from single-channel recorders or tions. Digital electrocardiographs are able to record the 8 in standard array from simultaneous-lead–acquisition de- channels of independent information simultaneously, with 4 vices, the sequence of limb lead presentation on ECG of the limb leads being derived from the other 2. Alignment recordings is historical, not anatomic. Thus, whereas V1 24 of separate channel writers must be precise to within 10 ms, through V6 progress leftward and slightly inferiorly across the and ideally less. The most commonly used output format precordium, the frontal plane limb leads follow no regular Downloaded from involves lead separation based on rows and columns. For order that allows individual leads to be compared easily with standard-sized paper, at 25 mm/s recording speed, four anatomically directly adjacent leads. For example, lead aVF 2.5-second columns can be presented sequentially on the represents the potential difference from a vector perspective page, with no time disruption between different columns. that is between lead III and lead II, but this is not easily Each column therefore represents successive 2.5-second in- appreciated from the standard array. Similarly, leads I and http://circ.ahajournals.org/ tervals of a continuous 10-second record. In the most tradi- aVL are progressively counterclockwise, in the anatomic tional simultaneous lead format, the first column records rows sense, from lead II. Lead aVR is often thought of as an representing simultaneous leads I, II, and III; the second intracavitary lead that looks toward the atria from the apex of column records rows representing simultaneous aVR, aVL, the ventricles, but inversion of aVR can be considered to and aVF; the third column represents simultaneous leads V1, represent a perspective that lies anatomically within the V2, and V3; the fourth column represents simultaneous leads counterclockwise progression from lead II to lead I.101 Use of V4,V5, and V6. Additional rows may be available for 1, 2, or inverted aVR has been reported to improve the diagnostic 3 leads of 10-second continuous recordings for rhythm

by guest on October 18, 2017 classification and estimation of risk associated with acute analysis. Alternatively, additional rows may be utilized to inferior and lateral myocardial infarction.104 present two 5-second recordings of 6 simultaneous limb leads and 6 simultaneous precordial leads, or 12 rows of simulta- Recommendations neous leads. Routine use of the Cabrera sequence for display of the limb leads can be highly recommended as an alternative presenta- Clinical Implications tion standard. For display in a format of 4 columns of 3 leads, The major advantage of simultaneous lead acquisition is that a left-to-right sequence (aVL to III) is logical because it is it allows precise temporal alignment of waveforms from closer to traditional placement of limb lead I at the upper left. different leads, which results in spatial-temporal insights that To maintain consistency, the left-to-right sequence is also have diagnostic value.97 By way of example, the temporal alignment of waveforms in aVR and aVL can aid in the recommended for horizontal display of the limb leads. How- diagnosis of fascicular block in the presence of infarction,98 ever, it is recognized that the current limb lead array is so whereas simultaneous views of P-wave and QRS waveforms deeply entrenched in ECG tradition that change might take in multiple leads can add information of value in the years to become generally accepted. At present, manufactur- interpretation of arrhythmias and in the diagnosis of myocar- ers should be encouraged to make this display available as a dial infarction.99 routine option in new electrocardiographs. Recommendation Alternative Lead Applications Standard tracings obtained with digital electrocardiographs should provide accurate temporal alignment of multiple leads, Torso and Other Modified Placement of the with maximum misalignment of no more than 10 ms, and Limb Leads ideally as little as is practically feasible. The printed tracing Technology may present temporally aligned groups of leads in different Noise from motion of the arms and legs during ambulatory formats according to preference. and exercise electrocardiography can be reduced by place- ment of the limb leads on the torso. In these diagnostic Alternative Information Format From applications, 12-lead ECGs have been recorded with the Standard Leads Mason-Likar lead position,105 in which the arm electrodes are Technology placed in the infraclavicular fossae medial to the deltoid The Cabrera or orderly sequence reorients the frontal plane insertions and the left leg electrode is placed midway between leads into a progressive anatomic array that extends logically the costal margin and iliac crest in the left anterior axillary 1316 Circulation March 13, 2007

line. More recent applications of the Mason-Likar monitoring mid sternum anteriorly, I at the right midaxillary line, and M position place the arm electrodes over the outer clavicles.81,106 at the mid spine posteriorly. In addition, electrode H is placed The precordial electrodes are placed in the standard positions. at the junction of the neck and torso posteriorly, and electrode An alternative modification of limb lead placement devel- F is placed on the left foot. Orthogonal lead information is oped for bicycle ergometry applies the arm electrodes to the constructed from modeled weighting of lead voltages. The upper outer arm and the leg electrodes to the anterior iliac EASI lead system is a reduced 5-lead set that uses the E, A, crest.107 Torso limb leads are sometimes used to reduce and I electrodes from the Frank lead system and adds an motion artifact from the arms and legs during recording in electrode, S, at the top of the mid sternum, along with a infants. ground reference electrode to provide orthogonally oriented signals.113 In addition to orthogonal data, transfer coefficients Clinical Implications Noise from motion of the limbs during routine ambulation have been developed for the EASI lead system that produce 114 and during exercise makes standard limb lead electrode synthesized 12-lead ECGs. Advantages of the EASI lead placement impractical for ECG monitoring. Typical monitor- system for patient monitoring applications are the absence of ing applications include bedside hard-wired or telemetered limb electrodes, which allows the patient to move around observation of rhythm and ST segments, quantitative ambu- without intolerable noise in the ECG signal, elimination of latory electrocardiography, and ECG recording during diag- the need to determine intercostal spaces, and avoidance of the nostic exercise testing.108 Rhythm diagnosis is not adversely breast.

Downloaded from affected by monitoring lead placement; however, tracings that Clinical Implications use torso electrodes differ in important ways from the Because monitoring applications of reduced lead sets are standard 12-lead ECG. In addition to body position differ- widespread and 12-lead reconstruction algorithms are avail- 109 ences that affect the ECG, monitoring electrodes placed on able in practice, it is important that the derived nature of these the trunk do not provide standard limb leads, and distortion of tracings is appreciated. The Frank lead system and other http://circ.ahajournals.org/ the central terminal alters the augmented limb leads and the vectorcardiographic lead systems produce the orthogonal X, precordial leads.110,111 Tracings with Mason-Likar and other Y, and Z components of the heart vector. These can be alternative lead placement may affect QRS morphology more combined into 3-dimensional vectorcardiographic loops dis- than repolarization compared with the standard ECG; these played in 2-dimensional planes (frontal, horizontal, and differences can include false-negative and false-positive in- sagittal); they can be directly examined as ECG voltage-time farction criteria.81,112 Motion artifact of the limbs is a partic- records as well. A number of transformations of orthogonal ular problem for routine recording in neonates, infants, and data can be used to produce a synthesized 12-lead ECG, but young children, in whom torso leads are sometimes used; the by guest on October 18, 2017 the generalized transfer coefficients used in these estimations clinical significance of the resulting differences remains to be established. are subject to individual variability in torso shape and heterogeneities of impedance. Patient-specific transforma- Recommendations tions derived from comparison with a baseline 12-lead ECG ECGs recorded with torso placement of the extremity elec- can improve the accuracy of subsequent synthesized tracings. trodes cannot be considered equivalent to standard ECGs for Torso inhomogeneities also limit the fidelity of synthesized all purposes and should not be used interchangeably with 12-lead tracings derived from EASI leads. An advantage of standard ECGs for serial comparison. Evaluation of the effect EASI leads is the relative anatomic simplicity of electrode of torso placement of limb leads on waveform amplitudes and placement. Tracings synthesized from the EASI leads have durations in infants is required. Tracings that use torso limb been shown to have useful correlative value with the standard lead placement must be clearly labeled as such, including 12-lead ECG115,116; however, it is recognized that these 12-lead tracings derived from torso limb lead placement in synthesized tracings can differ in interval duration and neonates or in young children and during ambulatory and amplitude from the corresponding standard ECGs. Whether exercise electrocardiography in adults. Furthermore, tracings synthesized 12-lead tracings provide practical advantage and recorded in the sitting or upright position should not be adequate reproduction of ST-segment shifts to be a substitute considered equivalent to standard supine ECGs. for standard tracings during acute ischemic syndromes is a matter of intense current investigation.117 Whether the accu- Reduced Lead Sets racy of these transformations for the monitoring of repolar- Technology ization changes can facilitate drug trials in ambulatory sub- It is possible to mathematically construct a synthesized jects is also under study. 12-lead ECG from reduced lead sets. These syntheses can approximate but not duplicate the tracing obtained by the Recommendations standard leads. The Frank lead system was devised as a lead Synthesized 12-lead ECGs are not equivalent to standard set suitable for obtaining reproducible orthogonal lead infor- 12-lead ECGs and cannot be recommended as a substitute for mation that could be used for vectorcardiography.5 The routine use. All 12-lead tracings derived by synthesis from system involves 7 electrodes, 5 of which are applied at points reduced lead sets must be clearly labeled as such. Although in the horizontal plane that intersect the fifth intercostal space synthesized ECGs that use the EASI lead system may be at the left sternal border: A at the left midaxillary line, C on demonstrably adequate for some purposes, such as monitor- the anterior left chest wall halfway between E and A, E at the ing of rhythm, they cannot be considered equivalent to Kligfield et al Standardization and Interpretation of the ECG, Part I 1317

standard 12-lead recordings or recommended at present as an guidelines that requires “ST elevation” in an intervention alternative for routine use. algorithm. Even so, ST elevation in posterior leads in acute posterior infarction is often Ͻ1 mm in amplitude, and Expanded Lead Sets because of lead orientation, proximity effect, and torso Technology inhomogeneity, it may not be equivalent in absolute magni- Hybrid lead systems, incorporating 3 Frank leads with the tude to the ST depression present in anterior leads. ST standard 12 leads, can be used by some electrocardiographs. elevation in 1 or more of the posterior leads has moderate Expanded lead sets include the multiple-electrode arrays used sensitivity and high specificity for posterior wall infarc- for body surface mapping of the electrical activity of the tion,130 but the value of these additional findings for the heart. Torso arrays include wraparound electrodes in multiple prediction of increased in-hospital complications is horizontal and vertical lines. Details of these arrays are unresolved.126,131 beyond the scope of the present report. Studies of body Recommendations surface maps recorded from large electrode arrays have Because treatment of infarction may vary with right ventric- provided useful information about localization of ECG infor- ular involvement, recording of additional right-sided pre- mation on the thorax, but their complexity precludes their use cordial leads during acute inferior-wall left ventricular infarc- as a substitute for the standard 12-lead ECG for routine tion is recommended. Routine recording of these leads in the recording purposes. Additional chest leads may be useful for absence of acute inferior infarction is not recommended. The

Downloaded from investigation of acute infarction. Four additional precordial use of additional posterior precordial leads can be recom- leads have been identified for use in this clinical setting (V R, 3 mended in settings in which treatment will depend on V R, V R, and V R), each of which is placed on the right side 4 5 6 documentation of ST elevation during infarction or other in mirror image to the standard precordial placement of . Routine recording of these addi- electrodes. Within this right-sided array of electrodes, stan- tional leads in the absence of an acute coronary syndrome is dard V can be considered equivalent to V R, and standard V http://circ.ahajournals.org/ 1 2 2 not recommended. As ST-segment vectors become increas- can be considered equivalent to V R. Examination of addi- 1 ingly used for improved diagnostic classification of myocar- tional posterior chest leads has been proposed for the identi- dial infarction, the addition of a frontal plane ST-segment fication of ST-elevation events in the posterior wall, includ- axis to the currently measured P-wave, QRS, and T-wave ing V (at the posterior axillary line), V (below the scapula), 7 8 axes in the ECG header data is recommended. and V9 (at the paravertebral border), each in the same 118–120 horizontal plane as V6. Lead Switches and Misplacements

by guest on October 18, 2017 Clinical Implications Limb Lead and Precordial Lead Switches Although acute right ventricular infarction can sometimes be Technology recognized from ST-segment elevation in V , studies dating 1 Lead switches (or more correctly, electrode cable switches) from the early 1980s have demonstrated that additional occur when a dedicated lead wire and electrode combination right-sided precordial leads have value for the diagnosis of is misplaced or when there is erroneous attachment of a acute right ventricular infarction in patients with inferior dedicated lead wire to individually placed electrodes. Color infarction.121–123 In this setting, ST-segment elevation ex- coding of lead wires is a feature of manufacturing standards ceeding 0.1 mV in 1 or more of the right precordial leads is for electrocardiographs,24 but even so, it is possible to moderately sensitive and specific for right ventricular injury misconnect lead wires at the cable terminal. Time-coherent and has been associated with underlying right ventricular P-wave morphology can be used to clarify lead switches,132 dysfunction124,125 and greater in-hospital complications.126 and these principles should be applicable to computer algo- Acute infarction of the posterior wall of the left ventricle rithms. Computer algorithms that are adaptable to computer- theoretically can be diagnosed from reciprocal ST-segment assisted electrocardiographs are capable of detecting lead depression evident in precordial leads V through V , and it 1 3 switches.133–137 appears that both the additional right-sided and additional posterior leads can be reconstructed from the standard ECG Clinical Implications leads.127 (Alternate description of this territory as anatomi- Lead switches are really switches of the cable connections of cally inferolateral rather than posterior will be discussed 2 or more properly placed electrodes. This can result in elsewhere.) Additional leads have not provided increased erroneous pairing within the standard limb leads or within the sensitivity for infarction in all studies128; however, ST- pairing of an exploring lead with the central terminal. When segment elevation over the posterior left chest has been an electrode that is switched involves the central terminal, all reported to be the only site of ST elevation found in some leads may be affected. Lead switches affect 2 or more of the cases of posterior infarction.118 Recent guidelines for inter- standard leads, thereby distorting the ECG recording. Limb vention in acute coronary syndromes differ in important ways lead switches can result in false-positive and false-negative for ST-elevation and for non–ST-elevation infarction.129 In signs of ischemia.138 Some of these changes can be recog- this sense, anterior ST depression during infarction from a nized by an alert technician or correctly interpreted by the spatial vector perspective may be electrocardiographically reviewing physician, particularly when previous ECGs are equivalent to posterior ST elevation, but it may be quite available, whereas others may go unrecognized or require different in terms of a literal interpretation of treatment repeat recording of the ECG.139 Transposition of the left and 1318 Circulation March 13, 2007

right arm lead wires produces inversion of limb lead I, with a and inferior-leftward misplacement of left precordial elec- switch of leads II and III and a switch of leads aVR and aVL, trodes in more than one third. whereas aVF remains unaltered. Because the central terminal Clinical Implications is unaffected, there are no changes in the precordial leads. In Lead placement variability between recordings is an impor- normal situations, lead I is generally similar to V with 6 tant reason for poor reproducibility of precordial ECG am- respect to the morphology of the P wave and QRS direction. plitude measurements.86,90,144 Reproducibility of duration A clue to distinction of these findings from those present in a measurements is generally better than reproducibility of patient with mirror-image dextrocardia is that lead misplace- amplitudes.145 It has been established that variation in pre- ment results in an important discordance between lead I and cordial lead placement of as little as 2 cm can result in V6. As a corollary, the ECG in a patient with mirror-image important diagnostic errors, particularly those that involve dextrocardia may be “normalized” by purposely reversing the statements about anteroseptal infarction and ventricular hy- left and right arm lead wires and using mirror-image right- pertrophy.142 Precordial lead misplacement can alter sided precordial leads. Transposition of the right arm and computer-based diagnostic statements in up to 6% of right leg lead wires is also easy to recognize, because lead II recordings.85 now records the nearly zero potential difference that exists between the 2 legs,140,141 which results in very low amplitude Recommendations only in lead II, with inverted symmetry between standard lead Periodic retraining in proper lead positioning of the pre- cordial leads should be routine for all personnel who are Downloaded from I and lead III. Transposition of the left arm and left leg lead wires is more difficult to recognize because the main effects responsible for the recording of ECGs. Serial tracings in acute are an often subtle shift in axis and inversion of lead III; it can or subacute care settings should make use of some form of be suspected from changes in P-wave morphology in the limb skin marking to promote reproducibility of lead placement when it is not possible to leave properly applied electrodes in leads,138 although the specificity of this approach has been 137 place. http://circ.ahajournals.org/ challenged. Suspected lead switches may be confirmed by reference to a prior or subsequent tracing with correct lead Computerized Interpretation of the ECG placement. Transposition of lead wires to V1 and V2,toV2 Technology and V3, or within all 3 leads can cause a reversal of R-wave progression that simulates anteroseptal wall infarction, but Two computer-based processes are required for diagnostic this artifact often can be recognized by distorted progression digital ECG programs that provide diagnostic interpretation. of the precordial P waves and T waves in the same leads. The first stage is preparation of the signal for analysis by the processing methods discussed above. As discussed in prior by guest on October 18, 2017 Recommendations sections of this statement, the fidelity of measurements used Medical personnel responsible for the recording of routine in diagnostic algorithms is determined by the technical issues ECGs should receive training on the avoidance of lead that affect signal processing.9,23,28,42,146 These signal- switches and guidelines for their recognition. Lead-switch processing methods include signal preparation (sampling, detection algorithms should be incorporated into digital filtering, and template formation), feature extraction, and electrocardiographs along with alarms for abnormally high measurement.147–151 Time-coherent simultaneous lead data lead impedance, and suspected misplacements should be and the construction of representative template complexes are identified to the person recording the ECG in time to correct critical to the reliability of feature extraction and measure- the problem. If not corrected before recording, a diagnostic ment; global measurements of duration may be systematically statement alerting the reader to the presence of different types smaller when time-coherent data are not used. The second of lead switches should be incorporated into preliminary stage of analysis applies diagnostic algorithms to the pro- interpretive reports. cessed ECG. Diagnostic algorithms may be heuristic (experience-based rules that are deterministic) or statistical Lead Misplacement (probabilistic) in structure. Heuristic diagnostic algorithms were originally designed to incorporate discrete measurement Technology thresholds into a decision tree or boolean combinations of ECG amplitudes and duration measurements vary with pre- criteria.152–155 Statistical diagnostic algorithms circumvent cordial lead placement, which often ranges widely from the problems of diagnostic instability that are associated with recommended anatomic sites.84,142 The early work of Kerwin small serial changes around discrete partitions by adding a et al143 demonstrated that reproducibility of precordial lead probability statement to the diagnosis. These may be based on placement to within 1 cm occurred only in about half of men bayesian logic.156 Other statistical methods use discriminant and in even fewer women. Placement accuracy during routine function analysis, which can use continuous ECG parameters electrocardiography appears to have decreased further with in addition to discrete variables to produce a point score.157,158 time. A recent study documented that fewer than two thirds of These algorithms tend to be more reproducible than earlier routinely applied precordial electrodes were applied within heuristic methods, even though they still may result in 1.25 inch of the designated landmark, but errors were not discrete thresholds for diagnostic statements. Neural nets distributed randomly.84 A more vertical distribution of pre- differ from conventional discriminant function analysis in the cordial electrodes than required resulted from superior mis- way they are trained, in the resulting classifier, and in their 133,159,160 placement of V1 and V2 electrodes in more than half of cases derived decision boundaries. Statistical methods de- Kligfield et al Standardization and Interpretation of the ECG, Part I 1319

pend on a database of well-documented cases to find the (median 91.3%) was lower than that for the cardiologists optimal ECG parameters to use. Such a database must be (median 96.0%), whereas important differences in overall large enough that the results are statistically reliable. The accuracy were found between different algorithms. Salerno et database must contain sufficient cases with varying degrees al18 reviewed 13 reports of computer ECG program perfor- of abnormality, ranging from mild to severe cases, and a mance and showed that these programs generally perform representative distribution of common confounding condi- less well than expert readers with respect to individual tions.6,9,17,161 The statistics of well-documented populations diagnoses. Even so, this report found that computer assistance have been used to develop diagnostic algorithms that no was able to improve the diagnostic performance of less expert longer simply mimic the human reader.162 Similarly, it has readers. also been shown that the addition of vector loop criteria (or the equivalent information deduced from simultaneous leads) Recommendations improves 12-lead ECG diagnoses.97,98 Computer-based interpretation of the ECG is an adjunct to the electrocardiographer,164 and all computer-based reports require Clinical Implications physician overreading. Accurate individual templates should be Given the potentially profound effects of technical factors on formed in each lead before final feature extraction and measure- ECG measurements, it is not surprising that identical diag- ment used for diagnostic interpretation. Time-coherent data from nostic algorithms might perform differently when applied to multiple leads should be used to detect the earliest onset and ECG signals that undergo processing by different methods. latest offset of waveforms of global measurements used for Downloaded from Adherence to methodological standards will minimize these diagnostic interpretation. Deterministic and statistical or proba- differences, promote uniformity of measurement and inter- bilistic algorithms should be based on well-constructed data- pretation, and facilitate serial comparison of tracings. Even bases that include varying degrees of pathology and an appro- with adherence to standards, small systematic differences in priate distribution of confounding conditions. Such algorithms measurements might be expected between diagnostic instru- should be validated with data that have not been used for http://circ.ahajournals.org/ ments that use different processing methods, particularly with development. Programs using complex diagnostic algorithms respect to diagnostically important global measures of QRS should document in reference material those measurements that duration and QT interval. A 1985 study by the European CSE are critical to the diagnostic statement, which might include group demonstrated that measurement differences among 10 synthesized vector loop or other novel measurements. Serial standard ECG systems could be large enough to alter diag- comparisons of sequential ECGs should be done by trained nostic conclusions17; however, no recent studies have directly observers regardless of whether the ECG program provides a compared template and global measurements made with the serial comparison. Assessment of the performance of different current generation of commercially available standard ECG by guest on October 18, 2017 algorithms will be facilitated by use of a standardized glossary of recording systems. Beyond the technical issues of measure- interpretive statements. ment fidelity, evaluation of the performance of ECG pro- grams is difficult.9,15,17,163 Programs may be compared with diagnoses of an expert cardiologist or consensus of expert Summary cardiologists or with diagnoses ascertained by independent The present document outlines the relation of the modern data. The CSE group evaluated 15 ECG and vectorcardio- digital electrocardiograph to its technology. Individual fea- graphic analysis programs against a reference database that tures of ECG processing and recording are considered in included documented cases of ventricular hypertrophy and terms of their clinical implications. Recommendations focus myocardial infarction,15 diagnoses that are strongly depen- on progress toward optimal use of the ECG. It is hoped that dent on accurate measurement of amplitudes and durations the standards set out in this document will provide a further and should favor computer analysis. Overall, the percentage stimulus to the improvement of ECG recording and of ECGs correctly classified by the computer programs interpretation. 1320 Circulation March 13, 2007

Disclosures Writing Group Disclosures

Other Speakers’ Research Research Bureau/ Ownership Consultant/Advisory Writing Group Member Employment Grant Support Honoraria Interest Board Other Paul Kligfield Weill Medical None None None Unilead (ECG Philips Medical,* None College of electrode Mortara Instrument,* Cornell University technology)– GE Healthcare,* limited Quinton Medical,* partner† MDS Pharma Services,† Cardiac Science* James J. Bailey National Institutes of Health None None None None None None Rory Childers University of Chicago None None None None None None Barbara J. Deal Northwestern University None None None None None None Leonard S. Gettes University of North Carolina None None None None None None E. William Hancock Stanford University None None None None Philips None Medical Center— Medical

Downloaded from retired Professor Emeritus Systems,† Covance Diagnostics† Jan A. Kors Erasmus Medical Center None None None None None None Peter Macfarlane University of Glasgow Cardiac Science,† None None None Garhard Schmidt None Medtronic,† Heartlab,† Consult,* http://circ.ahajournals.org/ Medcon,† Del Mar Reynolds,† Epiphany Drayer† Cardiography,* IqTeq,* Cardiolex* David M. Mirvis University of Tennessee None None None None None None Olle Pahlm Lund University, Sweden Philips Medical None None None None None Systems* Pentti Rautaharju Wake Forest None None None None Philips Medical None by guest on October 18, 2017 University Medical Systems† School–retired Gerard van Herpen Erasmus Medical Center None None None None None None Galen S. Wagner Duke University Medtronic,† None None None None None Medical Center Physiocontrol,† Welch Allyn† This table represents the relationships of writing group members that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all members of the writing group are required to complete and submit. A relationship is considered to be “significant” if (1) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (2) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant. Kligfield et al Standardization and Interpretation of the ECG, Part I 1321

Reviewer Disclosures

Other Research Research Speakers’ Ownership Consultant/ Reviewer Employment Grant Support Bureau/Honoraria Interest Advisory Board Other Jonathan Abrams University of New Mexico None None None None None None Leonard S. Dreifus Hahnemann University, None None None None None Merck School of Medicine Endpoint Committee Mark Eisenberg McGill University None None None None None None Nora Goldschlager University of California, San Francisco None None St. Jude, Medtronic None None None Peter Kowey Lankenau Hospital and Main Line Health None None Medifacts Cardionet Medifacts None Frank Marcus University of Arizona None None None None None None Thomas M. Munger Mayo Clinic St. Jude None None None None None Medical, Bard Electrophysiology Robert J. Myerburg University of Miami None None None None None None David Rosenbaum Case Western Reserve University None None None None None None Downloaded from Richard Schofield University of Florida None None None None None None Samuel Shubrooks Beth Israel Deaconess Medical Center None None None None None None Cynthia Tracy George Washington University None None None None None None This table represents the relationships of reviewers that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all reviewers are required to complete and submit. http://circ.ahajournals.org/

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William Hancock, Gerard van Herpen, Jan A. Kors, Peter Macfarlane, David M. Mirvis, Olle Pahlm, Pentti Rautaharju and Galen S. Wagner http://circ.ahajournals.org/ Circulation. 2007;115:1306-1324; originally published online February 23, 2007; doi: 10.1161/CIRCULATIONAHA.106.180200 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 2007 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. Online ISSN: 1524-4539 by guest on October 18, 2017

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AHA/ACC/HRS Scientific Statement

Recommendations for the Standardization and Interpretation of the Electrocardiogram Part II: Electrocardiography Diagnostic Statement List A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology

Jay W. Mason, MD, FAHA, FACC, FHRS; E. William Hancock, MD, FACC; Leonard S. Gettes, MD, FAHA, FACC Downloaded from Abstract—This statement provides a concise list of diagnostic terms for ECG interpretation that can be shared by students, teachers, and readers of electrocardiography. This effort was motivated by the existence of multiple automated diagnostic code sets containing imprecise and overlapping terms. An intended outcome of this statement list is greater uniformity of ECG diagnosis and a resultant improvement in patient care. The lexicon includes primary diagnostic http://circ.ahajournals.org/ statements, secondary diagnostic statements, modifiers, and statements for the comparison of ECGs. This diagnostic lexicon should be reviewed and updated periodically. (Circulation. 2007;115:1325-1332.) Key Words: AHA Scientific Statements Ⅲ electrocardiography Ⅲ computers Ⅲ diagnosis

his is the second of 6 articles designed to upgrade the vague terminology. Some statements that are commonly used by guidelines for the standardization and interpretation of electrocardiographers but that do not provide diagnostically or by guest on October 18, 2017 T the ECG. The project was initiated by the American Heart clinically useful information are not included. Some statements Association and has been endorsed by the American College have been excluded to reduce the size of the statement set, so of Cardiology, the Heart Rhythm Society, and the Interna- long as their meaning is well represented by included terms. tional Society for Computerized Electrocardiography. The The Writing Group believes that the listing should be imple- rationale for this upgrade and a description of the process are mented as an available lexicon in report algorithms of the contained in Part I by Kligfield et al.1 existing commercial electrocardiographs and that it should be The listing contained in the present statement seeks to present used widely by ECG readers. The principal advantage of such a limited set of ECG diagnostic statements that are clinically use would be a worldwide improvement in uniformity of ECG useful and that do not create unnecessary overlap or contain interpretation. Such uniformity would promote better patient

Other members of the Standardization and Interpretation of the Electrocardiogram Writing Group include James J. Bailey, MD; Rory Childers, MD; Barbara J. Deal, MD, FACC; Mark Josephson, MD, FACC, FHRS; Paul Kligfield, MD, FAHA, FACC; Jan A. Kors, PhD; Peter Macfarlane, DSc; Olle Pahlm, MD, PhD; David M. Mirvis, MD, FAHA; Peter Okin, MD, FACC; Pentti Rautaharju, MD, PhD; Borys Surawicz, MD, FAHA, FACC; Gerard van Herpen, MD, PhD; Galen S. Wagner, MD; and Hein Wellens, MD, FAHA, FACC. The American Heart Association, the American College of Cardiology, and the Heart Rhythm Society make every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on October 26, 2006, by the American College of Cardiology Board of Trustees on October 12, 2006, and by the Heart Rhythm Society on September 6, 2006. This article has been copublished in the March 13, 2007, issue of the Journal of the American College of Cardiology and in the March 2007 issue of Heart Rhythm. Copies: This document is available on the World Wide Web sites of the American Heart Association (www.americanheart.org) and the American College of Cardiology (www.acc.org). A single reprint is available by calling 800-242-8721 (US only) or writing the American Heart Association, Public Information, 7272 Greenville Ave, Dallas, TX 75231-4596. Ask for reprint No. 71-0390. To purchase additional reprints, call 843-216-2533 or e-mail [email protected]. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.americanheart.org/presenter.jhtml? Identifierϭ4431. A link to the “Permission Request Form” appears on the right side of the page. © 2007 American Heart Association, Inc., the American College of Cardiology Foundation, and the Heart Rhythm Society. Circulation is available at http://www.circulationaha.org DOI: 10.1161/CIRCULATIONAHA.106.180201 1325 1326 Circulation March 13, 2007

care. Additional advantages would be facilitation of the estab- statements could be made in comparing individual ECGs to lishment of a uniform teaching curriculum in electrocardiogra- Ն1 previous ECGs, the Writing Group recommends use of phy, availability of a uniform glossary of terms for research these 6 statements to convey clinically important information application, and promotion of research to better validate diag- that could influence patient care by the attending physician nostic criteria for the specific terms in the limited lexicon. while preserving brevity and uniformity. On the other hand, Although we recognize that each vendor of ECGs possesses a the Writing Group encourages readers to add uncoded text as proprietary set of diagnostic statements and underlying criteria, needed to the report to more fully compare tracings. we hope that this list of statements will be made available by Tables 5, 6, and 7 establish rules for use of the primary, each of them so that the reader can select it as the primary secondary, and modifier statements, alone or in combination. dictionary for use in interpreting all or some ECGs. We are also Table 8 is a set of commonly used statements that can, for the hopeful that the vendors will collaborate among themselves to most part, be precisely reproduced by use of the primary and align diagnostic criteria for this specific lexicon. This would not secondary statements and their modifiers. These statements are interfere with continued development of entirely independent, commonly used concatenations provided for the convenience of proprietary diagnostic software by each manufacturer. the reader.

Organization and Use Criteria for Diagnoses Four lists are included within this document. The main listing This listing does not specify diagnostic criteria for any of the statements. A single set of diagnostic criteria underlying the

Downloaded from (Table 1), “Primary Statements,” displays 117 primary diagnos- core statements would have great benefits for patient care and tic statements under 14 categories. The majority of the primary research. Although the Writing Group does not believe that a statements are nondescriptive and convey clinical meaning uniform criterion set can be achieved at this time, we without additional statements. The second listing (Table 2), encourage ECG vendors and electrocardiography researchers “Secondary Statements,” provides additional statements that can and experts to collaborate on the development of a univer- be used to expand the specificity and clinical relevance of both http://circ.ahajournals.org/ sally acceptable criteria set and a means for perpetually descriptive and other primary diagnostic statements. These refining it. Several of the chapters in this statement support secondary statements are divided into 2 groups. Those that are specific criteria for some of the core statements. preceded by “suggests” invoke clinical diagnoses likely respon- sible for the ECG observation(s). Those that are preceded by Myocardial Infarction Terminology Ͼ “consider” are intended to propose at least 1, but sometimes 1, Advanced imaging techniques, including echocardiography2 potentially associated clinical disorder. This set of primary and and magnetic resonance,3,4 have demonstrated a need for secondary diagnostic statements constitutes what we might call change in existing terminology describing the cardiac loca- by guest on October 18, 2017 the “core statement lexicon.” tion of myocardial infarction. New diagnostic statements for The third list (Table 3) contains adjectives that can be used 6 common, distinct cardiac locations of myocardial infarc- to modify the diagnostic statements. None of the modifiers tion, documented by contrast-enhanced magnetic resonance, change the meaning of the core statement but rather serve to were recently recommended by a committee of the Interna- refine the meaning. The list contains general modifiers, which tional Society for Holter and Noninvasive Electrocardiogra- can be used with many of the core statements, and specific phy.5 At the present time, the Writing Group considers the modifiers assigned to a specific category of statements. quantity of new data insufficient to recommend abandonment The fourth list (Table 4) is a short directory of comparison of existing terminology. Thus, traditional terms are listed in statements. It specifies 6 types of ECG changes that merit “Section M: Myocardial infarction” of the primary statement mention in the ECG interpretation and defines criteria to table (Table 1); however, we intend to revisit this issue when identify change within the 6 categories. Because so many sufficient data have been developed.

Disclosures

Writing Group Disclosures

Research Other Research Speakers’ Ownership Consultant/ Writing Group Member Employment Grant Support Bureau/Honoraria Interest Advisory Board Other Jay W. Mason Covance Cardiac Safety Services None None None None None None Leonard S. Gettes University of North Carolina None None None None None None E. William Hancock Stanford University Medical Center None None None None Philips Medical Systems,* None Covance Diagnostics* This table represents the relationships of writing group members that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all members of the writing group are required to complete and submit. A relationship is considered to be “significant” if (1) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (2) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Significant. Mason et al Standardization and Interpretation of the ECG, Part II 1327

Reviewer Disclosures

Research Other Research Speakers’ Ownership Consultant/ Reviewer Employment Grant Support Bureau/Honoraria Interest Advisory Board Other Jonathan Abrams University of New Mexico None None None None None None Leonard S. Dreifus Hahnemann University, School of Medicine None None None None None Merck Endpoint Committee Mark Eisenberg McGill University None None None None None None Nora Goldschlager University of California, San Francisco None None St. Jude; Medtronic None None None Peter Kowey Lankenau Hospital and Main Line Health None None Medifacts Cardionet Medifacts None Frank Marcus University of Arizona None None None None None None Thomas M. Munger Mayo Clinic St. Jude None None None None None Medical, Bard Electrophysiology Robert J. Myerburg University of Miami None None None None None None David Rosenbaum Case Western Reserve University None None None None None None Richard Schofield University of Florida None None None None None None Downloaded from Samuel Shubrooks Beth Israel Deaconess Medical Center None None None None None None Cynthia Tracy George Washington University None None None None None None This table represents the relationships of reviewers that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all reviewers are required to complete and submit. http://circ.ahajournals.org/ References magnetic resonance imaging. J Cardiovasc Magn Reson. 2004;6: 653–661. 1. Kligfield P, Gettes L, Bailey JJ, Childers R, Deal BJ, Hancock EW, van 4. Bayes de Luna A, Cino JM, Pujadas S, Cygankiewicz I, Carreras F, Herpen G, Kors JA, Macfarlane P, Mirvis DM, Pahlm O, Rautaharju P, Garcia-Moll X, Noguero M, Fiol M, Elosua R, Cinca J, Pons-Llado G. Wagner GS. Recommendations for the standardization and interpretation Concordance of electrocardiographic patterns and healed myocardial of the electrocardiogram: part I: the electrocardiogram and its technology: infarction location detected by cardiovascular magnetic resonance. a scientific statement from the American Heart Association Electrocar- Am J Cardiol. 2006;97:443–451. diography and Arrhythmias Committee, Council on Clinical Cardiology; 5. Bayes de Luna A, Wagner G, Birnbaum Y, Nikus K, Fiol M, Gorgels A, the American College of Cardiology Foundation; and the Heart Rhythm

by guest on October 18, 2017 Cinca J, Clemmensen PM, Pahlm O, Sclarovsky S, Stern S, Wellens J, Society. Circulation. 2007;115:–. Zareba W; International Society for Holter and Noninvasive Electrocar- 2. Bogaty P, Boyer L, Rousseau L, Arsenault M. Is anteroseptal myocardial diography. A new terminology for left ventricular walls and location of infarction an appropriate term? Am J Med. 2002;113:37–41. myocardial infarcts that present Q wave based on the standard of cardiac 3. Selvanayagam JB, Kardos A, Nicolson D, Francis J, Petersen SE, Robson magnetic resonance imaging: a statement for healthcare professionals M, Banning A, Neubauer S. Anteroseptal or apical myocardial infarction: from a committee appointed by the International Society for Holter and a controversy addressed using delayed enhancement cardiovascular Noninvasive Electrocardiography. Circulation. 2006;114:1755–1760. 1328 Circulation March 13, 2007

TABLE 1. Primary Statements

A. Overall interpretation G. Ventricular tachyarrhythmias 1 Normal ECG 70 Ventricular 2 Otherwise normal ECG 71 , unsustained 3 Abnormal ECG 72 Ventricular tachycardia, polymorphous 4 Uninterpretable ECG 73 Ventricular tachycardia, torsades de B. Technical conditions pointes 10 Extremity electrode reversal 74 Ventricular 11 Misplaced precordial electrode(s) 75 Fascicular tachycardia 12 Missing lead(s) 76 Wide-QRS tachycardia 13 Right-sided precordial electrode(s) H. Atrioventricular conduction 14 Artifact 80 Short PR interval 15 Poor-quality data 81 AV conduction ratio N:D 16 Posterior electrode(s) 82 Prolonged PR interval C. Sinus node rhythms and arrhythmias 83 Second-degree AV block, Mobitz type I 20 Sinus rhythm (Wenckebach) Downloaded from 21 84 Second-degree AV block, Mobitz type II 22 Sinus 85 2:1 AV block 23 Sinus 86 AV block, varying conduction 24 , type I 87 AV block, advanced (high-grade) 25 Sinoatrial block, type II 88 AV block, complete (third-degree) http://circ.ahajournals.org/ 26 Sinus pause or arrest 89 AV dissociation 27 Uncertain supraventricular rhythm I. Intraventricular and intra-atrial D. Supraventricular arrhythmias conduction 30 Atrial premature complex(es) 100 Aberrant conduction of supraventricular beat(s) 31 Atrial premature complexes, nonconducted 101 Left anterior fascicular block Left posterior fascicular block 32 Retrograde atrial activation 102 by guest on October 18, 2017 Left bundle-branch block 33 Wandering atrial pacemaker 104 Incomplete right bundle-branch block 34 Ectopic atrial rhythm 105 Right bundle-branch block 35 Ectopic atrial rhythm, multifocal 106 Intraventricular conduction delay 36 Junctional premature complex(es) 107 Ventricular preexcitation 37 Junctional escape complex(es) 108 Right atrial conduction abnormality 38 Junctional rhythm 109 Left atrial conduction abnormality 39 Accelerated junctional rhythm 110 Epsilon wave 40 Supraventricular rhythm 111 41 Supraventricular complex(es) J. Axis and voltage Right-axis deviation 42 Bradycardia, nonsinus 120 Left-axis deviation E. Supraventricular tachyarrhythmias 121 Right superior axis 50 122 Indeterminate axis 51 123 Electrical alternans 52 Ectopic , unifocal 124 Low voltage 53 Ectopic atrial tachycardia, multifocal 125 Abnormal precordial R-wave progression 54 128 Abnormal P-wave axis 55 Supraventricular tachycardia 131 56 Narrow-QRS tachycardia K. Chamber hypertrophy or F. Ventricular arrhythmias enlargement 140 Left 60 Ventricular premature complex(es) 61 Fusion complex(es) 141 Left ventricular hypertrophy 62 Ventricular escape complex(es) 142 Right ventricular hypertrophy 63 Idioventricular rhythm 143 Biventricular hypertrophy 64 Accelerated idioventricular rhythm 144 65 Fascicular rhythm 66 Parasystole Mason et al Standardization and Interpretation of the ECG, Part II 1329

TABLE 1. Primary Statements, Cont’d TABLE 2. Secondary Statements

L. ST segment, T wave, and U Suggests⅐⅐⅐ wave 200 Acute 145 ST deviation 201 Acute pulmonary embolism 146 ST deviation with T-wave change 202 Brugada abnormality 147 T-wave abnormality 203 Chronic pulmonary disease 148 Prolonged QT interval 204 CNS disease 149 Short QT interval 205 Digitalis effect 150 Prominent U waves 206 Digitalis toxicity 151 Inverted U waves 207 Hypercalcemia 152 TU fusion 208 Hyperkalemia 153 ST-T change due to ventricular 209 Hypertrophic hypertrophy 210 Hypocalcemia 154 Osborn wave 211 Hypokalemia or drug effect 155 Early repolarization 212 Hypothermia M. Myocardial infarction

Downloaded from 213 Ostium primum ASD 160 Anterior MI 214 161 Inferior MI 215 Sinoatrial disorder 162 Posterior MI Consider⅐⅐⅐ 163 Lateral MI 220 Acute ischemia 165 Anteroseptal MI http://circ.ahajournals.org/ 221 AV nodal reentry 166 Extensive anterior MI 222 AV reentry 173 MI in presence of left bundle-branch block 223 Genetic repolarization abnormality 174 Right ventricular MI 224 High precordial lead placement N. Pacemaker 225 Hypothyroidism 180 Atrial-paced complex(es) or rhythm 226 Ischemia 227 Left ventricular aneurysm by guest on October 18, 2017 181 Ventricular-paced complex(es) or rhythm 182 Ventricular pacing of non–right ventricular 228 Normal variant apical origin 229 Pulmonary disease 183 Atrial-sensed ventricular-paced 230 Dextrocardia complex(es) or rhythm 231 Dextroposition 184 AV dual-paced complex(es) or rhythm CNS indicates central nervous system; ASD, atrial septal defect; and AV, 185 Failure to capture, atrial atrioventricular. 186 Failure to capture, ventricular 187 Failure to inhibit, atrial 188 Failure to inhibit, ventricular 189 Failure to pace, atrial 190 Failure to pace, ventricular AV indicates atrioventricular; MI, myocardial infarction. 1330 Circulation March 13, 2007

TABLE 3. Modifiers

General Myocardial infarction, cont’d 301 Borderline 332 Old 303 Increased 333 Of indeterminate age 304 Intermittent 334 Evolving 305 Marked Arrhythmias and tachyarrhythmias 306 Moderate 340 Couplets 307 Multiple 341 In a bigeminal pattern 308 Occasional 342 In a trigeminal pattern 309 One 343 Monomorphic 310 Frequent 344 Multifocal 312 Possible 345 Unifocal 313 Postoperative 346 With a rapid ventricular response 314 Predominant 347 With a slow ventricular response 315 Probable 348 With capture beat(s)

Downloaded from 316 Prominent 349 With aberrancy 317 (Specified) Lead(s) 350 Polymorphic 318 (Specified) Electrode(s) Repolarization abnormalities 321 Nonspecific 360 Ն0.1 mV General: conjunctions 361 Ն0.2 mV http://circ.ahajournals.org/ 302 Consider 362 Depression 310 Or 363 Elevation 320 And 364 Maximally toward lead 319 With 365 Maximally away from lead 322 Versus 366 Low amplitude Myocardial infarction 367 Inversion 330 Acute 369 Postpacing (anamnestic) by guest on October 18, 2017 331 Recent

TABLE 4. Comparison Statements

Code Statement Criteria 400 No significant change Intervals (PR, QRS, QTc) remain normal or within 10% of a previously abnormal value No new or deleted diagnoses with the exception of normal variant diagnoses 401 Significant change in rhythm New or deleted rhythm diagnosis HR change Ͼ20 bpm and Ͻ50 or Ͼ100 bpm New or deleted pacemaker diagnosis 402 New or worsened ischemia or infarction Added infarction, ST-ischemia, or T-wave-ischemia diagnosis, or worsened ST deviation or T-wave abnormality 403 New conduction abnormality Added AV or IV conduction diagnosis 404 Significant repolarization change New or deleted QT diagnosis New or deleted U-wave diagnosis New or deleted nonischemic ST or T-wave diagnosis Change in QTc Ͼ60 ms 405 Change in clinical status New or deleted diagnosis from Axis and Voltage, Chamber Hypertrophy, or Enlargement primary statement categories or “Suggests⅐⅐⅐” secondary statement category 406 Change in interpretation without significant change in Used when a primary or secondary statement is added or removed despite no real change in waveform the tracing; ie, an interpretive disagreement exists between the readers of the first and second ECGs QTc indicates corrected QT interval; HR, heart rate; bpm, beats per minute; AV, atrioventricular; and IV, intraventricular. Mason et al Standardization and Interpretation of the ECG, Part II 1331

TABLE 5. General Use Rules TABLE 6. Secondary–Primary Statement Pairing Rules

1 Secondary statements must be accompanied by a primary statement Secondary Code May Accompany These Primary Codes 2 Modifiers must be accompanied by a primary statement 200 145–147 3 A primary statement may be accompanied by nothing, by Ն1 201 21, 105, 109, 120, 131, 141, 145–147 Ն modifiers, by 1 secondary statements, or by both. 202 105, 106, 145–146 4 Each secondary statement can accompany only certain primary 203 109, 120, 125, 128, 131, 141, 143 statements (see Table 6) 204 147 5 Each general modifier can accompany only certain primary statements (see Table 7) 205 145–147 6 Each specific modifier can accompany only primary statements within 206 145–147 its category 207 149 208 147 209 142 210 148 211 147–148, 150 212 14, 154

Downloaded from 213 82, 105–106, 121 214 124 215 42, 131, 145–147 220 145–147, 151 221 55, 56 http://circ.ahajournals.org/ 222 55, 56 223 148, 149 224 128 225 22, 24–26, 37, 38 226 145–147 227 145–147 228 80, 105, 128, 155 by guest on October 18, 2017 229 109, 120, 122–123, 125, 128, 131, 141, 143 230 128, 131 231 128 1332 Circulation March 13, 2007

TABLE 7. General Modifier–Primary Statement Pairing Rules*

General Modifier May (May Not) Accompany These Primary Codes or May Be May/ Code Between Codes in These Categories or Groups of Categories May Not Location 301 1–20, 24–76, 81, 83–106, 108, 122–124 May not b 302 1–3, 12–16, 80–82, 111–130, 145–152 May not b, i 303 30, 31, 36, 37, 41, 60, 62, 63, 82, 107, 109, 110 May a, b 304 21–26, 30–76, 80, 82–108, 124, 180–190 May b 305 1–20, 27–76, 81, 85–106, 111, 122, 123, 148–150, 160–190 May not b 306 1–20, 27–76, 81, 85–106, 111, 122, 123, 148–150, 160–190 May not b 307 26, 30, 31, 36, 37, 41, 60–62, 185–190 May b 308 26, 30, 31, 36, 37, 41, 60–62, 185–190 May b 309 26, 30, 31, 36, 37, 41, 60–62, 185–190 May b 310 C, D, E, F, G, N, H, I, J, K, L, M May i 312 1–3, 15, 80–82, 120–122, 128 May not b 313 145–147 May b 314 20–23, 33–35, 38–56, 63–76, 83–89, 180–184 May b Downloaded from 315 1–3, 15, 80–82, 120–122, 128 May not b 316 1–20, 27–76, 81, 85–106, 111, 122, 123, 148–150, 160–190 May not b 317 C, D, E, F, G, N, H, I, J, K, L, M May i 318 C, D, E, F, G, N, H, I, J, K, L, M May i http://circ.ahajournals.org/ 319 C, D, E, F, G, N, 100, J, K, L, M May i 321 40, 55, 56, 145–147 May b b indicates before; a, after; and i, between. *Not inclusive. by guest on October 18, 2017 TABLE 8. Convenience Statements*

Code Statement 500 Nonspecific ST-T abnormality 501 ST elevation 502 ST depression 503 LVH with ST-T changes Others to be added LVH indicates left ventricular hypertrophy. *This table will be developed independently by each ECG laboratory. Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part II: Electrocardiography Diagnostic Statement List: A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: Endorsed by the International Society for Computerized Electrocardiology Downloaded from Jay W. Mason, E. William Hancock and Leonard S. Gettes

Circulation. 2007;115:1325-1332; originally published online February 23, 2007;

http://circ.ahajournals.org/ doi: 10.1161/CIRCULATIONAHA.106.180201 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 2007 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. Online ISSN: 1524-4539 by guest on October 18, 2017 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://circ.ahajournals.org/content/115/10/1325

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AHA/ACCF/HRS Scientific Statement

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram Part III: Intraventricular Conduction Disturbances A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology

Borys Surawicz, MD, FAHA, FACC; Rory Childers, MD; Barbara J. Deal, MD, FACC; Leonard S. Gettes, MD, FAHA, FACC Downloaded from

he present article introduces the second part of “Recom- The term intraventricular conduction disturbances refers Tmendations for Standardization and Interpretation of the to abnormalities in the intraventricular propagation of su- Electrocardiogram.” The project was initiated by the Council praventricular impulses that give rise to changes in the shape on Clinical Cardiology of the American Heart Association and/or duration of the QRS complex. These changes in http://circ.ahajournals.org/ and has been endorsed by the American College of Cardiol- intraventricular conduction may be fixed and present at all ogy, the Heart Rhythm Society, and the International Society heart rates, or they may be intermittent and be tachycardia or for Computerized Electrocardiography. This statement was bradycardia dependent. They may be caused by structural preceded by 2 articles, “The Electrocardiogram and Its abnormalities in the His-Purkinje conduction system or ven- Technology” and “Diagnostic Statements,” which were pub- tricular myocardium that result from necrosis, fibrosis, calci- lished previously,1,2 and it is followed by statements concern- fication, infiltrative lesions, or impaired vascular supply. ing abnormalities of repolarization, hypertrophy, and ische- Alternatively, they may be functional and due to the arrival of

by guest on October 18, 2017 mia/infarction. The rationale for this initiative and the process a supraventricular impulse during the relative refractory by which it was achieved were described earlier.1 period in a portion of the conducting system, in which case

Other members of the Standardization and Interpretation of the Electrocardiogram Writing Group include James J. Bailey, MD; Anton Gorgels, MD; E. William Hancock, MD, FACC; Mark Josephson, MD, FACC, FHRS; Paul Kligfield, MD, FAHA, FACC; Jan A. Kors, PhD; Peter Macfarlane, DSc; Jay W. Mason, MD, FAHA, FACC, FHRS; David M. Mirvis, MD; Peter Okin, MD, FACC; Olle Pahlm, MD, PhD; Pentti M. Rautaharju, MD, PhD; Gerard van Herpen, MD, PhD; Galen S. Wagner, MD; and Hein Wellens, MD, FAHA, FACC. The American Heart Association, the American College of Cardiology, and the Heart Rhythm Society make every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest. Parts I and II of this series, “Recommendations for the Standardization and Interpretation of the Electrocardiogram,” were published in the March 13, 2007, issue of Circulation (Circulation. 2007;115:1306–1324 and 1325–1332). They are available online at http://circ.ahajournals.org/content/vol115/issue10/ Parts III, IV, V, and VI of this series are available online at http://circ.ahajournals.org/content/vol119/issue10/ (Circulation. 2009;119:e235–e240; e241–e250; e251–e261; and e262–e270). They also published ahead of print February 19, 2009. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on August 7, 2008, by the American College of Cardiology Board of Trustees on May 16, 2008, and by the Heart Rhythm Society on June 18, 2008. The American Heart Association requests that this document be cited as follows: Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation. 2009;119:e235–e240. This article has been copublished in the Journal of the American College of Cardiology. Copies: This document is available on the World Wide Web sites of the American Heart Association (my.americanheart.org), the American College of Cardiology (www.acc.org), and the Heart Rhythm Society (www.hrsonline.org). A copy of the document is also available at http://www. americanheart.org/presenter.jhtml?identifierϭ3003999 by selecting either the “topic list” link or the “chronological list” link (No. LS-1886). To purchase additional reprints, call 843-216-2533 or e-mail [email protected]. Expert peer review of AHA Scientific Statements is conducted at the AHA National Center. For more on AHA statements and guidelines development, visit http://www.americanheart.org/presenter.jhtml?identifierϭ3023366. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.americanheart.org/presenter.jhtml? identifierϭ4431. A link to the “Permissions Request Form” appears on the right side of the page. (Circulation. 2009;119:e235-e240.) © 2009 American Heart Association, Inc, American College of Cardiology Foundation, and the Heart Rhythm Society. Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.108.191095 e235 e236 Circulation March 17, 2009

the term aberrant ventricular conduction is applied. They Table. Mean Frontal Plane Axis may also be due to abnormal atrioventricular connections, QRS Axis which bypass the atrioventricular node, resulting in ventric- Age Normal Values Abnormal Values Description ular preexcitation. Adult Ϫ30° to 90° ϽϪ30° Left-axis deviation In 1985, the electrocardiography (ECG) criteria for intra- Ϫ30° to Ϫ45° Moderate left-axis ventricular conduction disturbances and ventricular preexci- deviation tation were reviewed by an ad hoc working group established Ϫ45° to Ϫ90° Marked left-axis by the World Health Organization and the International deviation Society and Federation of Cardiology. Recommendations 90° to 120° Moderate right-axis were made for the diagnosis of complete and incomplete left deviation and right bundle-branch blocks (LBBB and RBBB), left 120° to 180° Marked right-axis anterior and left posterior fascicular blocks, nonspecific deviation 3 intraventricular blocks, and ventricular preexcitation. The 8 to 16 y 0° to 120° Ͼ120° Right-axis deviation purpose of the present report is to define the normal QRS 5 to 8 y 0° to 140° Ͼ140° Right-axis deviation duration, review the recommendations made in 1985, recom- Ͻ0° Left-axis deviation mend alterations and additions to those recommendations, Ͼ and provide recommendations for children and adolescents. 1 to 5 y 5° to 100° 100° Right-axis deviation 1 mo to 1 y 10° to 120° Ͼ120° Right-axis deviation Downloaded from Normal QRS Duration Ͻ10° to Ϫ90° Left-axis deviation The QRS duration depends on the method of measurement, Neonate 30° to 190° Ͼ190° to Ϫ90° Extreme right-axis age, and gender. Global intervals, from the earliest onset to deviation the latest offset of the waveform in all leads (generally taken Ͻ30° to ϽϪ90° Left-axis deviation

http://circ.ahajournals.org/ from a spatial vector magnitude or superimposed complexes), are the desirable standard. Global intervals, by definition, will Mean Frontal Plane Axis be longer than measurements from single leads. QRS duration The mean frontal plane electrical axis, determined by the may increase with increasing heart size. In addition, the QRS vector of the maximal (dominant) QRS deflection, depends complex is wider in the precordial than in the limb leads. on age and body habitus (Table). It shifts to the left with There are also age- and gender-dependent differences in increasing age. In adults, the normal QRS axis is consid- children and adolescents. In children less than 4 years of age, ered to be within Ϫ30° and 90°. Left-axis deviation is a QRS duration of 90 ms or more is considered to be by guest on October 18, 2017 Ϫ30° and beyond. Moderate left-axis deviation is between prolonged, and in those whose ages are 4 to 16 years, a QRS Ϫ30° and Ϫ45°. Marked left-axis deviation is from Ϫ45° 4 duration of 100 ms or more is considered to be prolonged. In to Ϫ90° and is often associated with left anterior fascicular 5 adult males, the QRS duration may be up to 110 ms. In 725 block. Moderate right-axis deviation in adults is from 90° normal males more than 18 years of age, QRS duration to 120°, and marked right-axis deviation, which is often 6 ranged from 74 to 114 ms, with an average of 95 ms. associated with left posterior fascicular block, is between Because global data and data detailing the effects of age, 120° and 180°. In the absence of a dominant QRS 7–10 gender, and race are still evolving, the committee recom- deflection, as in an equiphasic QRS complex, the axis is mends that for the present, a QRS duration of greater than 110 said to be indeterminate. ms in subjects older than 16 years of age be regarded as In children, there is normally a rightward QRS axis at birth abnormal. The data for both children and adults may have to that shifts gradually leftward throughout childhood. In the be revised in the near future. neonate, the mean electrical axis in the frontal plane is between 60° and 190° and is termed “extreme right axis” Review of Prior Recommendations With when it is between Ϫ90° and 190°. Normally, the axis then Revisions Proposed by the Committee shifts to the left, and by ages 1 to 5 years, it is generally The committee recommends that the definitions and criteria between 10° and 110°.4 Between 5 and 8 years of age, the for mean frontal plane electrical axis and axis deviation, normal QRS axis may extend to 140°, and between ages 8 and R-wave peak time (defined as the interval from the onset of 16 years, the range of QRS axis extends to 120°. Leftward the QRS complex to the peak of the R wave in leads that do QRS-axis shifts are present in congenital defects with under- not have a small initial R wave, in preference to the term development of the right ventricle, such as tricuspid atresia, intrinsicoid deflection), complete and incomplete RBBB, and with abnormal location of the conduction system, such as complete and incomplete LBBB, left anterior and left poste- complete atrioventricular septal defect. rior fascicular block, nonspecific , ven- tricular preexcitation, and the Wolff-Parkinson-White pattern Complete RBBB 3 and syndrome defined in 1985 be retained, with the inclusion 1. QRS duration greater than or equal to 120 ms in adults, of appropriate values for pediatric subjects, including mean greater than 100 ms in children ages 4 to 16 years, and frontal plane axis and axis deviation. These definitions and greater than 90 ms in children less than 4 years of age.

criteria, with the revisions proposed by the committee, are 2. rsrЈ, rsRЈ,orrSRЈ in leads V1 or V2. The RЈ or rЈ deflection presented below. is usually wider than the initial R wave. In a minority of Surawicz et al Standardization and Interpretation of the ECG, Part III e237

patients, a wide and often notched R wave pattern may be children less than 8 years of age without criteria for RBBB or seen in lead V1 and/or V2. LBBB. The definition may also be applied to a pattern with 3. S wave of greater duration than R wave or greater than 40 RBBB criteria in the precordial leads and LBBB criteria in ms in leads I and V6 in adults. the limb leads, and vice versa. 4. Normal R peak time in leads V5 and V6 but Ͼ50 ms in lead V1. Left Anterior Fascicular Block Of the above criteria, the first 3 should be present to 1. Frontal plane axis between Ϫ45° and Ϫ90°. make the diagnosis. When a pure dominant R wave with or 2. qR pattern in lead aVL. without a notch is present in V1, criterion 4 should be 3. R-peak time in lead aVL of 45 ms or more. satisfied. 4. QRS duration less than 120 ms.

Incomplete RBBB These criteria do not apply to patients with congenital Incomplete RBBB is defined by QRS duration between 110 heart disease in whom left-axis deviation is present in and 120 ms in adults, between 90 and 100 ms in children infancy. between 4 and 16 years of age, and between 86 and 90 ms in children less than 8 years of age. Other criteria are the same Left Posterior Fascicular Block as for complete RBBB. In children, incomplete RBBB may 1. Frontal plane axis between 90° and 180° in adults. Owing be diagnosed when the terminal rightward deflection is less to the more rightward axis in children up to 16 years of age,

Downloaded from than 40 ms but greater than or equal to 20 ms. The ECG this criterion should only be applied to them when a pattern of incomplete RBBB may be present in the absence distinct rightward change in axis is documented.

of heart disease, particularly when the V1 lead is recorded 2. rS pattern in leads I and aVL. higher than or to the right of normal position and rЈ is less 3. qR pattern in leads III and aVF. than 20 ms. 4. QRS duration less than 120 ms. The terms rsrЈ and normal rsrЈ are not recommended to http://circ.ahajournals.org/ describe such patterns, because their meaning can be vari- Ventricular Preexcitation of Wolff-Parkinson- White Type ously interpreted. In children, an rsrЈ pattern in V1 and V2 with a normal QRS duration is a normal variant. Whether preexcitation is full or not cannot be determined from the body surface ECG, but the following criteria are Complete LBBB suggestive of full preexcitation: 1. QRS duration greater than or equal to 120 ms in adults, greater than 100 ms in children 4 to 16 years of age, and 1. PR interval (assuming no intra-atrial or interatrial conduc-

by guest on October 18, 2017 greater than 90 ms in children less than 4 years of age. tion block) less than 120 ms during sinus rhythm in adults

2. Broad notched or slurred R wave in leads I, aVL, V5, and and less than 90 ms in children. V6 and an occasional RS pattern in V5 and V6 attributed to 2. Slurring of initial portion of the QRS complex (delta wave), displaced transition of QRS complex. which either interrupts the P wave or arises immediately after

3. Absent q waves in leads I, V5, and V6, but in the lead aVL, its termination. a narrow q wave may be present in the absence of 3. QRS duration greater than 120 ms in adults and greater myocardial pathology. than 90 ms in children.

4. R peak time greater than 60 ms in leads V5 and V6 but 4. Secondary ST and T wave changes. normal in leads V1,V2, and V3, when small initial r waves can be discerned in the above leads. Terms Not Recommended 5. ST and T waves usually opposite in direction to QRS. The term Mahaim-type preexcitation is not recommended 6. Positive T wave in leads with upright QRS may be normal because the diagnosis cannot be made with certainty on the (positive concordance). basis of the surface ECG. The terms atypical LBBB, bilateral 7. Depressed ST segment and/or negative T wave in leads bundle-branch block, , and trifascicular with negative QRS (negative concordance) are abnor- mal11,12 and are discussed in part VI of this statement. block are not recommended because of the great variation in 8. The appearance of LBBB may change the mean QRS axis anatomy and pathology producing such patterns. The com- in the frontal plane to the right, to the left, or to a superior, mittee recommends that each conduction defect be described in some cases in a rate-dependent manner.13,14 separately in terms of the structure or structures involved instead of as bifascicular, trifascicular, or multifascicular Incomplete LBBB block. 1. QRS duration between 110 and 119 ms in adults, between The term Brugada pattern to describe a pattern that 90 and 100 ms in children 8 to 16 years of age, and simulates incomplete RBBB in lead V1 with ST-segment between 80 and 90 ms in children less than 8 years of age. changes is not recommended for incorporation into auto- 2. Presence of left ventricular hypertrophy pattern. mated interpretative algorithms because there are 3 differ- 3. R peak time greater than 60 ms in leads V4,V5, and V6. ent types of ST-segment changes15,16 and because the 4. Absence of q wave in leads I, V5, and V6. pattern is not specific for the Brugada syndrome. The use Nonspecific or Unspecified Intraventricular of this term should be left to the discretion of the Conduction Disturbance overreader. QRS duration greater than 110 ms in adults, greater than 90 The term left septal fascicular block is not recommended ms in children 8 to 16 years of age, and greater than 80 ms in because of the lack of universally accepted criteria. e238 Circulation March 17, 2009

Additional Terms and directed opposite to the Q wave (ie, a QR complex in the Peri-infarction block17,18: The term possible peri-infarction inferior or lateral leads). block is recommended when, in the presence of an abnormal Peri-ischemic block19,20: This term is recommended when Q wave generated by a myocardial infarction in the inferior or a transient increase in QRS duration accompanies the ST- lateral leads, the terminal portion of the QRS complex is wide segment deviation seen with acute injury.

Disclosures

Writing Group Disclosures

Writing Group Other Research Speakers’ Ownership Consultant/Advisory Member Employment Research Grant Support Bureau/Honoraria Interest Board Other James J. Bailey National Institutes of None None None None None None Health Rory Childers University of Chicago None None None None None None Barbara J. Deal Northwestern None None None None None None University Leonard S. Gettes University of North None None None None None None Carolina Downloaded from Anton Gorgels University Hospital None None None None None None Maastricht E. William Stanford University None None None None Philips Medical None Hancock Medical Center Systems†; Covance (retired Professor Diagnostics† Emeritus) http://circ.ahajournals.org/ Mark Josephson Harvard Medical None None None None Medtronic* None Faculty Physicians for Beth Israel Deaconess Medical Center Paul Kligfield Weill Medical College None None None None Philips Medical*; None of Cornell University Mortara Instrument*; GE Healthcare*; MDS by guest on October 18, 2017 Pharma Services†; Cardiac Science* Jan A. Kors Erasmus Medical None None None None None Welch Allyn* Center Peter Macfarlane University of Glasgow Cardiac Science Corp†; None None None Cardiac Science None Medtronic Physio Corp†; Medtronic Control†; Spacelabs Physio Control†; Health Care†; Draeger Spacelabs Health Medical†; Heartlab†; Care†; Draeger McKesson† Medical†; Heartlab†; McKesson† Jay W. Mason Independent None None None None None None Consultant David M. Mirvis University of None None None None None None Tennessee Peter Okin Weill Medical College Merck† None None None None None of Cornell University Olle Pahlm BFC Klin None None None None None None Pentti M. Wake Forest None None None None Philips Medical None Rautaharju University Medical Systems† School (retired) Borys Surawicz CARE Group None None None None None None Gerard van Herpen Erasmus Medical None None None None None Welch Allyn* Center Galen S. Wagner Duke University Medtronic†; None None None None None Medical Center Physiocontrol†; Welch Allyn† (Continued) Surawicz et al Standardization and Interpretation of the ECG, Part III e239

Writing Group Disclosures, Continued

Writing Group Other Research Speakers’ Ownership Consultant/Advisory Member Employment Research Grant Support Bureau/Honoraria Interest Board Other Hein Wellens University of None None None None Medtronic* None Maastricht This table represents the relationships of writing group members that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all members of the writing group are required to complete and submit. A relationship is considered to be “significant” if (1) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (2) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant.

Reviewer Disclosures

Speakers’ Research Other Research Bureau/ Expert Ownership Consultant/Advisory Reviewer Employment Grant Support Honoraria Witness Interest Board Other Downloaded from Jeffrey L. Intermountain Medical None None None None None None None Anderson Center Leonard S. Dreifus Hahnemann University None None None None None None None Hospital Mark Eisenberg McGill University None None None None None None None http://circ.ahajournals.org/ Nora Goldschlager University of None None None None None None None California, San Francisco Cindy Grines William Beaumont None None None None None None None Hospital Mark Hlatky Stanford University None None None None None None None Peter Kowey Lankenau Medical None None None None CardioNet† Transoma*; CardioNet†; None

by guest on October 18, 2017 Office NewCardio* Rachel Lampert Yale University Medtronic†; None None None None Medtronic* None Guidant/Boston Scientific†; St. Jude† Robert Lichtenberg Heart Care Centers of None None None None None None None Illinois Jonathan Lindner Oregon Health and Genentech* None None None None Genentech*; None Sciences University VisualSonics* Frank Marcus University of Arizona None None None None None None None Robert J. University of Miami None None None None None None None Myerburg Gerald M. Pohost University of Southern None None None None None None None California, Keck School of Medicine Richard Schofield University of Florida None None None None None None None Health Sciences Center Samuel Shubrooks Beth Israel Deaconess None None None None None None None Medical Center John Strobel IMA, Inc None None None None None None None Stuart A. Winston Michigan Heart, PC; Medtronic*; None Boston None None None None Ann Arbor Boston Scientific* Scientific* This table represents the relationships of reviewers that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all reviewers are required to complete and submit. A relationship is considered to be “significant” if (1) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (2) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant. e240 Circulation March 17, 2009

References 10. Rijnbeek PR, Witsenburg M, Schrama E, et al. New normal limits for the 1. Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the stan- paediatric electrocardiogram. Eur Heart J. 2001;22:702–11. dardization and interpretation of the electrocardiogram, part I: the elec- 11. Sgarbossa EB, Pinski SL, Barbagelata A, et al; GUSTO-1 (Global Utili- trocardiogram and its technology: a scientific statement from the zation of Streptokinase and Tissue Plasminogen Activator for Occluded American Heart Association Electrocardiography and Arrhythmias Com- Coronary Arteries) Investigators. Electrocardiographic diagnosis of mittee, Council on Clinical Cardiology; the American College of Car- evolving acute myocardial infarction in the presence of left bundle-branch diology Foundation; and the Heart Rhythm Society. Circulation. 2007; block [published correction appears in N Engl J Med. 1996;334:931]. 115:1306–24. N Engl J Med. 1996;334:481–7. 2. Mason JW, Hancock EW, Gettes L, et al. Recommendations for the 12. Gunnarsson G, Eriksson P, Dellborg M. ECG criteria in diagnosis of standardization and interpretation of the electrocardiogram, part II: elec- acute myocardial infarction in the presence of left . trocardiography diagnostic statement list: a scientific statement from the Int J Cardiol. 2001;78:167–72. American Heart Association Electrocardiography and Arrhythmias Com- 13. Swiryn S, Abben R, Denes P, Rosen KM. Electrocardiographic deter- mittee, Council on Clinical Cardiology; the American College of Car- minants of axis during : study in patients with diology Foundation; and the Heart Rhythm Society. Circulation. 2007; intermittent left bundle branch block. Am J Cardiol. 1980;46:53–8. 115:1325–32. 14. Childers R, Lupovich S, Sochanski M, Konarzewska H. Left bundle branch 3. Willems JL, Robles de Medina EO, Bernard R, et al. Criteria for intra- block and : a report of 36 cases. J Electrocardiol. 2000; ventricular conduction disturbances and pre-excitation: World Health 33(suppl):93–102. Organization/International Society and Federation for Cardiology Task 15. Alings M, Wilde A. “Brugada” syndrome: clinical data and suggested Force Ad Hoc. J Am Coll Cardiol. 1985;5:1261–75. pathophysiological mechanism. Circulation. 1999;99:666–73. 4. Davignon A, Rautaharju P, Boisselle E, et al. Normal ECG standards for 16. Eckardt L, Probst V, Smits JP, et al. Long term prognosis of individuals with infants and children. Pediatr Cardiol. 1980;1:123–31. right precordial ST-segment–elevation Brugada syndrome. Circulation. 5. Lepeschkin E, Surawicz B. The measurement of the duration of the QRS 2005;111:257–63.

Downloaded from interval. Am Heart J. 1952;44:80–8. 17. Grant RP. Peri-infarction block. Prog Cardiovasc Dis. 1959;2:237–47. 6. MacFarlane PW, Lawrie TDV. The normal electrocardiogram and vector 18. Vassallo JA, Cassidy DM, Marchlinski FE, et al. Abnormalities of endo- cardiogram. In: Macfarlane PW, Lawrie TDV, eds. Comprehensive Elec- cardial activation pattern in patients with previous healed myocardial trocardiology: Theory and Practice in Health Disease. New York, NY: infarction and ventricular tachycardia. Am J Cardiol. 1986;58:479–84. Pergamon Press; 1989:424–49. 19. Wagner NB, Sevilla DC, Krucoff MW, et al. Transient alterations of the 7. Matthes T, Gottsch G, Zywietz C. Interactive analysis of statistical ECG QRS complex and ST segment during percutaneous transluminal balloon diagnosis on an intelligent electrocardiograph: an expert system approach. angioplasty of the left anterior descending coronary artery. Am J Cardiol. http://circ.ahajournals.org/ In: Willems JL, van Bemmel JH, Zywietz C, eds. Computer ECG Anal- ysis: Towards Standardization. New York, NY: Elsevier; 1986:215–20. 1988;62:1038–142. 8. Wu J, Kors JA, Rijnbeek PR, et al. Normal limits of the electrocardio- 20. Surawicz B. Reversible QRS changes during acute myocardial ischemia. gram in Chinese subjects. Int J Cardiol. 2003;87:37–51. J Electrocardiol. 1998;31:209–20. 9. Macfarlane PW, McLaughlin SC, Devine B, Yang TF. Effects of age, sex, and race on ECG interval measurements. J Electrocardiol. 1994; KEY WORDS: AHA Scientific Statements Ⅲ electrocardiography Ⅲ 27(suppl):14–9. electrophysiology Ⅲ conduction Ⅲ IVCD by guest on October 18, 2017 AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part III: Intraventricular Conduction Disturbances: A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: Endorsed by the International Society for Computerized Electrocardiology Downloaded from Borys Surawicz, Rory Childers, Barbara J. Deal and Leonard S. Gettes

Circulation. 2009;119:e235-e240; originally published online February 19, 2009;

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AHA/ACCF/HRS Scientific Statement

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram Part IV: The ST Segment, T and U Waves, and the QT Interval A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology

Pentti M. Rautaharju, MD, PhD; Borys Surawicz, MD, FAHA, FACC; Leonard S. Gettes, MD, FAHA, FACC

Downloaded from he present article is the fourth in a series of 6 documents ditions, the transmembrane voltage changes slowly during this Tfocused on providing current guidelines for the standard- phase and remains at approximately the same level in all ization and interpretation of the electrocardiogram (ECG). The ventricular myocardial cells. As a result, only small voltage project was initiated by the Council on Clinical Cardiology of gradients are present. This absence of pronounced voltage the American Heart Association. The rationale for this project gradients is similar to that which occurs during electric diastole, http://circ.ahajournals.org/ and the process for its implementation were described earlier.1 ie, from the end of repolarization to the onset of the next Abnormalities in the ST segment, T wave, and duration of depolarization, when ventricular myocardial cells are at their the QT interval reflect abnormalities in ventricular repolar- resting transmembrane potential of approximately Ϫ85 mV. ization. These abnormalities are common and often difficult This corresponds to the TP segment on the ECG. The absence of to interpret. The U wave most likely represents an electric- significant voltage gradients in ventricular myocardial cells mechanical phenomenon that occurs after repolarization is during these 2 phases of the cardiac cycle explains why the ST completed. However, it is frequently included in discussions and TP segments are normally nearly flat and at approximately of repolarization and is discussed in this section. the same level; that is, they are isoelectric. by guest on October 18, 2017 The ST segment corresponds to the plateau phase of the The T wave corresponds to the phase of rapid ventricular ventricular transmembrane action potential. Under normal con- repolarization (phase 3) of the ventricular action potential.

Other members of the Standardization and Interpretation of the Electrocardiogram Writing Group include James J. Bailey, MD; Rory Childers, MD; Barbara J. Deal, MD, FACC; Anton Gorgels, MD; E. William Hancock, MD, FACC; Mark Josephson, MD, FACC, FHRS; Paul Kligfield, MD, FAHA, FACC; Jan A. Kors, PhD; Peter Macfarlane, DSc; Jay W. Mason, MD, FAHA, FACC, FHRS; David M. Mirvis, MD; Peter Okin, MD, FACC; Olle Pahlm, MD, PhD; Gerard van Herpen, MD, PhD; Galen S. Wagner, MD; and Hein Wellens, MD, FAHA, FACC. The American Heart Association, the American College of Cardiology, and the Heart Rhythm Society make every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest. Parts I and II of this series, “Recommendations for the Standardization and Interpretation of the Electrocardiogram,” were published in the March 13, 2007, issue of Circulation (Circulation. 2007;115:1306–1324 and 1325–1332). They are available online at http://circ.ahajournals.org/content/vol115/issue10/ Parts III, IV, V, and VI of this series are available online at http://circ.ahajournals.org/content/vol119/issue10/ (Circulation. 2009;119:e235–e240; e241–e250; e251–e261; and e262–e270). They also published ahead of print February 19, 2009. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on August 7, 2008, by the American College of Cardiology Board of Trustees on May 16, 2008, and by the Heart Rhythm Society on June 18, 2008. The American Heart Association requests that this document be cited as follows: Rautaharju PM, Surawicz B, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part IV: the ST segment, T and U waves, and the QT interval: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation. 2009;119:e241–e250. This article has been copublished in the Journal of the American College of Cardiology. Copies: This document is available on the World Wide Web sites of the American Heart Association (my.americanheart.org), the American College of Cardiology (www.acc.org), and the Heart Rhythm Society (www.hrsonline.org). A copy of the document is also available at http://www.americanheart. org/presenter.jhtml?identifierϭ3003999 by selecting either the “topic list” link or the “chronological list” link (No. LS-1887). To purchase additional reprints, call 843-216-2533 or e-mail [email protected]. Expert peer review of AHA Scientific Statements is conducted at the AHA National Center. For more on AHA statements and guidelines development, visit http://www.americanheart.org/presenter.jhtml?identifierϭ3023366. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.americanheart.org/presenter.jhtml? identifierϭ4431. A link to the “Permission Request Form” appears on the right side of the page. (Circulation. 2009;119:e241-e250.) © 2009 American Heart Association, Inc, American College of Cardiology Foundation, and the Heart Rhythm Society. Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.108.191096 e241 e242 Circulation March 17, 2009

During this phase, the transmembrane action potential repo- cally as changes in QRS shape and/or duration, are referred to larizes from its plateau voltage of approximately 10 to Ϫ10 as secondary repolarization abnormalities. These changes do mV to its resting level of approximately Ϫ85 mV. The not require changes in the shape or duration of phase 2 and interventricular and intraventricular voltage gradients created phase 3 of ventricular action potential of individual cells. as the cells undergo rapid sequential repolarization generate Rather, they may be due to voltage gradients that are the T wave on the body surface ECG. The configuration of normally largely canceled but become manifest when the the T wave is determined by the spatial-temporal character- changes in the sequence of depolarization alter the repolar- istics of ventricular repolarization, particularly the asyn- ization sequence. The ST- and T-wave changes that occur in chrony of phase 3 of the ventricular action potentials. Our association with bundle-branch blocks, ventricular preexcita- knowledge of these characteristics is still incomplete. In tion, and ectopic and paced ventricular complexes are exam- general, repolarization proceeds from epicardium to endocar- ples of secondary repolarization abnormalities. dium, that is, opposite to the direction of ventricular depo- The classic ventricular gradient concept introduced by larization,2,3 and probably, like during excitation, a signifi- Wilson et al10 in 1931 is of some theoretical interest concern- cant fraction of simultaneous repolarization wave fronts are ing primary versus secondary repolarization abnormalities. mutually canceled. The difference in the spatial sequence of Ventricular gradient in a single ECG lead is the net time depolarization and repolarization in the left ventricular free integral of the ECG voltage from the beginning of the P wave wall reflects the observation that there tends to be an inverse to the end of the U wave. Its spatial counterpart is the relationship between activation time and action potential ventricular gradient vector determined from the orthogonal Downloaded from duration.4 The action potential duration of epicardial cells is XYZ leads. The practical utility of the ventricular gradient in shorter than that of the endocardial and midmyocardial cells.5 differentiating primary from secondary repolarization abnor- In addition, it is known that inhomogeneities of repolarization malities has not been demonstrated.11 When the direction of occur over relatively short distances on the surface of the the QRS axis is normal, an abnormal direction of the T-wave ventricles and most probably also within the ventricular axis is generally an indication of primary repolarization http://circ.ahajournals.org/ wall.5,6 It is probable that some of these inherent action abnormalities. potential differences are the result of electrotonic interactions Recognition of secondary repolarization abnormalities is during repolarization.7 usually not difficult. In left bundle-branch block, the ST- Abnormalities in the ST segment and T wave are caused by segment and T-wave vectors are generally directed opposite abnormal voltage gradients during the plateau and rapid to the mean QRS vector. In right bundle-branch block, they repolarization phases of the action potential and by changes are directed opposite to the slow terminal component of the in the sequence of repolarization that may occur both with QRS complex. In ventricular preexcitation, ST-T changes are

by guest on October 18, 2017 and without abnormal voltage gradients. These abnormalities directed opposite to the delta wave of the QRS complex. The are often associated with a variety of well-defined anatomic, magnitude of the ST-T change is dependent on the magnitude pathological, physiological, and pharmacological events. of the QRS-waveform changes when the excitation pathways In this section, we address several issues relative to the change. measurement, description, and interpretation of ST segment, The secondary ST- and T-wave changes associated with T and U waves, and QT interval. They include the distinction transiently altered ventricular conduction such as those that between primary and secondary repolarization abnormalities, occur with ectopic ventricular complexes or transient bundle- appropriate descriptive and interpretive terminology, and branch blocks usually revert promptly to the pattern that measurement of the QT interval and its adjustment for rate, existed before the ventricular conduction changes developed. gender, and QRS duration. However, some secondary repolarization changes take longer (hours or days) to develop and to dissipate. The repolarization Distinction Between Primary and Secondary changes associated with prolonged ventricular pacing are Repolarization Abnormalities examples of this phenomenon.12 Abnormalities in the ST segment and T wave, which are the Primary and secondary repolarization abnormalities may result of changes in the shape and/or duration of the repolar- occur concurrently. For example, ventricular hypertrophy is ization phases of the transmembrane action potential and associated with changes in the shape and duration of the occur in the absence of changes in depolarization, are referred ventricular action potential of isolated ventricular cells, par- to as primary repolarization abnormalities. They may be ticularly on the endocardial surface.13 These changes may localized or diffuse and may be caused by a variety of events, contribute to ST- and T-wave changes and are independent of including ischemia, , drugs, toxins, and electro- the changes that are secondary to QRS-amplitude changes lyte abnormalities, particularly abnormalities of serum cal- and prolongation of the QRS complex. A combination of cium and potassium. An abrupt change in heart rate, hyper- primary and secondary repolarization abnormalities should ventilation, changes in body position, catecholamines, also be considered when T-wave polarity does not change as sympathetic stimulation or ablation of the stellate ganglion, anticipated by the changes in the QRS complex. and temperature changes also can cause primary repolariza- tion abnormalities.8,9 Recommendation Abnormalities in the ST segment and T wave that occur as The distinction between primary and secondary repolariza- the direct result of changes in the sequence and/or duration of tion abnormalities is clinically relevant because primary ventricular depolarization, manifested electrocardiographi- abnormalities indicate changes in the repolarization charac- Rautaharju et al Standardization and Interpretation of the ECG, Part IV e243

teristics of ventricular myocytes whereas secondary changes older and 0.25 mV for men less than 40 years of age. The

do not. The designation of the ST- and T-wave abnormalities recommended threshold value for adult women in V2 and V3 is as primary or secondary is appropriate, and it is recom- 0.15 mV. The threshold recommended for abnormal J-point mended that automated interpretative algorithms be pro- elevation for men and women in all other standard leads is 0.1 grammed to identify them. mV. These threshold values appear to be an appropriate com- promise for practical clinical use in the evaluation of ST ST-Segment Abnormalities elevation. ST- and T-wave amplitudes are referenced against the TP or In the evaluation of ST elevation, it is important to consider PR segments of the ECG. When low-frequency filtering is ST-segment waveform in addition to the normal limits for ST done in ECG acquisition to remove baseline drift, the actual amplitudes. The ST segment in normal J-point elevation in V2 DC voltage levels of various ECG waves or segments cannot and particularly V1 is generally sloping down steeply. Normal be determined. Thus, elevation of the ST segment may reflect ST elevation at 60 ms past the J point is combined with an PR/TP depression, true ST elevation, or both; conversely, ST upsloping ST segment rather than with the more horizontal depression may reflect PR/TP elevation, true ST depression, ST segment present in myocardial ischemia. or both.14–16 When considering deviations of the ST segment, The reference values established in adequately large one should bear in mind total QRS amplitude because this population-based normal groups stratified by age, gender, and variable also affects the amplitude of ST-segment abnormal- race should be incorporated into computer-ECG ST-segment ities. Displacement of the ST segment is usually measured at classification algorithms to avoid the inappropriate diagnosis Downloaded from its junction with the end of the QRS complex, the “J point,” of injury currents associated with myocardial ischemia, myo- and, in some settings such as exercise testing, 40 and up to 80 cardial infarction, or pericarditis. ms after the J point. The ST segment can be described as ST-segment elevation can most often be attributed to 3 elevated, depressed, upsloping, horizontal, or downsloping. specific causes: (1) a normal variant, frequently referred to as In addition, the magnitude of abnormal deviations and the early repolarization, commonly characterized by J-point http://circ.ahajournals.org/ leads showing them should be identified. A depressed ST elevation and rapidly upsloping or normal ST segment; (2) segment may be further characterized as horizontal, injury currents associated with acute ischemia or ventricular downsloping, or upsloping (rapidly or slowly). dyskinesis; and (3) injury currents usually associated with pericarditis. Criteria exist to differentiate these causes22–24 Elevation of the ST segment in leads V1,V2, and V3 should be referenced against the elevation that occurs normally in and should be incorporated into the descriptive and diagnostic algorithms of the various computer-ECG algorithms. However, these leads and is greater in young and middle-aged males it is important to recognize that in practice it is often difficult to than in females17–21 and greater in blacks than in whites.21 ST differentiate between them. In addition, a variety of other by guest on October 18, 2017 elevation is usually most pronounced in chest lead V . The 2 conditions may be associated with ST-segment elevation. upper normal limit for J-point elevation in V varies to a 2 ST depression may be caused by various physiological, certain degree in various reference sources, probably largely pathological, and pharmacological interventions that change as a result of differing selection criteria for the normal group. the plateau phase of the ventricular action potential. Exam- One reference source20 reports the upper 98th percentile ples include the effects of ischemia, hypokalemia, and a normal limit as approximately 0.3 mV in white men less than variety of cardiac and noncardiac drugs. These are primary 40 years of age (up to 0.33 mV in the 24- to 29-year age ST-segment changes. Depression of the ST-segment also may group) and approximately 0.25 mV in white men 40 years old occur concurrently with T-wave changes. Examples include and older. The corresponding limits for white women re- the ST-segment depression associated with hypertrophy and, mained relatively unchanged with age, staying at approxi- as secondary repolarization abnormalities, in ventricular con- mately 0.15 mV. duction disturbances. 21 Another reference source lists normal limits for J-point The ST-segment changes on the standard ECG that are and ST60 (ST at 60 ms past the J point) amplitudes for white associated with acute ischemia or infarction are due to the and black men and women 40 years old and older in 2 age flow of current across the boundary between the ischemic and groups. The upper normal limit (98th percentile) for J-point nonischemic zones referred to as injury current. ST-segment amplitude in V2 was approximately 0.15 mV in white men elevation generally occurs with reciprocal ST depression in and 0.20 mV in black men. The corresponding limits were ECG leads in which the axis is opposite in direction from approximately 0.10 mV for white women and 0.15 mV for those with ST elevation. These ST-segment abnormalities are black women. The upper normal limits for ST60 in V2 were discussed in part VI (Acute Ischemia/Infarction),66 which approximately 0.3 mV in white men and approximately 0.35 gives Ϫ0.05 as the recommended threshold value for abnor- mV in black men. The corresponding limits were approxi- mal J- point depression in leads V2 and V3 in men and women mately 0.2 mV in white women and approximately 0.25 mV and Ϫ0.1 mV in all other leads. in black women. Consideration of ST-segment changes as a response to Evaluation of ST elevation is of particular concern in exercise stress testing is outside the scope of the present connection with myocardial ischemia in acute myocardial working group. infarction, as discussed in detail in part 6 of this series of recommendations (Acute Ischemia/Infarction). The threshold Recommendation

value for abnormal J-point elevation in V2 and V3 recom- Although it may be difficult to differentiate various causes of mended in that part is 0.2 mV for men 40 years of age and ST-segment abnormalities, the ECG interpretative report e244 Circulation March 17, 2009

should include a qualitative description of the ST segment ular conduction should be labeled as such. ST- and T-wave with due consideration of the age and gender of the patient, changes associated with hypertrophy, hypokalemia, and including a note if ST depression is 0.1 mV or more drugs can be attributed to one of these factors. Giant T-wave pronounced. One or more of the possible causes, depending inversion is usually limited to one of several entities, includ- on the presence of other ECG abnormalities and the knowl- ing hypertrophic , non–ST-segment eleva- edge of any pertinent clinical information, also may be tion myocardial infarctions, and neurological events, partic- included. For evaluation of ST elevation, reference values ularly intracranial hemorrhage. The interpretation of such T- established in adequately large population-based normal wave changes should be descriptive, and a statement listing groups stratified by age, gender, and race should be the most common causes is appropriate. incorporated into computer-ECG ST-segment classifica- It is virtually impossible to develop a cause-specific tion algorithms to avoid the inappropriate diagnosis of classification for minor T-wave abnormalities. For these, injury currents associated with myocardial ischemia/infarc- classification as slight or indeterminate T-wave abnormality tion or pericarditis. is appropriate. The overreader can then apply analysis of other features, and the clinical condition if available, to T-Wave Abnormalities provide a more likely list of diagnostic possibilities. In these Just as ST-segment segment abnormalities can occur with or situations, comparison with prior ECGs (if available) is often without T-wave abnormalities, T-wave abnormalities can helpful. occur in the presence or absence of ST-segment segment

Downloaded from Notching of the T wave may be difficult to discriminate abnormalities. The T-wave amplitude in limb leads is influ- from a U wave that is superimposed on the downslope of an enced by the frontal-plane T axis, which in turn is influenced upright T wave. It is important to recognize that the T wave by the QRS axis. is rarely notched in all 12 leads and that the interval between In children older than 1 month, the T wave is often inverted the 2 summits of a notched T wave is usually less than the in leads V1,V2, and V3. In adolescents 12 years old and older interval between the peak of a monophasic T wave and the U http://circ.ahajournals.org/ and in young adults less than 20 years of age, the T wave may wave, which usually exceeds 150 ms at heart rates of 50 to be slightly inverted in aVF and inverted in lead V2. In adults 100 bpm.26 20 years old and older, the normal T wave is inverted in aVR;

upright or inverted in leads aVL, III, and V1; and upright in Recommendation

leads I and II and in chest leads V3 through V6. The ECG report should include a description of T-wave In evaluations of T-wave abnormalities, T-wave negativity abnormalities, identification of associated ST-segment

in lateral chest leads V5 and V6 is clinically particularly changes if present, and a statement as to whether the changes

by guest on October 18, 2017 important. In these leads, the T wave is slightly negative (less are indeterminate or more likely to be associated with a than 0.1 mV) in 2% of white men and women 60 years of age specific cause. and older and in 2% of black men and women 40 years of age and older; it is negative by 0.1 mV or more in 5% of black T-Wave Alternans men and women 60 years of age and older.21 T-wave alternans signifies T-wave amplitude variations that In normal adults, the T-wave amplitude is most positive in alternate every second beat. These amplitude variations are

lead V2 or V3. The reported normal standards for the T wave quantified with various modifications of moving-average in various reports from community-based populations vary to analysis or as the variance of specific frequency components some extent by age, gender, and race.20,21 T-wave amplitudes in spectral analysis. T-wave alternans is typically observed as

for V2 from 1.0 to 1.4 mV have been listed as upper normal microvolt-level variation (microvolt T-wave alternans) and, thresholds in men (up to 1.6 mV in the 18- to 29-year age at times, as more pronounced variations in alternating com- group) and from 0.7 up to 1.0 mV in women. plexes or as slower components outside the range of the A number of terms such as peaked, symmetrical, biphasic, proper T-wave alternans, generally most prominent in phase flat, and inverted are being used as appropriate qualitative T- with respiration. wave descriptors. As more quantitative descriptors, it is T-wave alternans indicates latent instability of repolariza-

proposed that the T wave in leads I, II, aVL, and V2 to V6 be tion predictive of malignant arrhythmias. It is generally not reported as inverted when the T-wave amplitude is from Ϫ0.1 present at the resting state even in high-risk patients, and a to Ϫ0.5 mV, as deep negative when the amplitude is from stress test (exercise or pharmacological stress or pacing), Ϫ0.5 to Ϫ1.0 mV, and as giant negative when the amplitude requiring special equipment and analysis software, is needed is less than Ϫ1.0 mV.25 In addition, the T wave may be called to provoke it. These procedures are outside the scope of the low when its amplitude is less than 10% of the R-wave present document. It is sufficient to state that although the amplitude in the same lead and as flat when the peak T-wave role of T-wave alternans regarding its clinical utility has not amplitude is between 0.1 and Ϫ0.1 mV in leads I, II, aVL been fully defined, it holds substantial potential in identifying

(with an R wave taller than 0.3 mV), and V4 to V6. patients at high risk of serious arrhythmic events. Interpreting isolated T-wave abnormalities is difficult and often the source of ambiguous and inaccurate statements. The The U Wave inappropriate diagnoses of myocardial ischemia and infarc- The U wave is a mechanoelectric phenomenon26 that results tion are common errors. As indicated above, ST- and T-wave in a low-amplitude, low-frequency deflection that occurs after abnormalities that are secondary to abnormalities in ventric- the T wave. It is frequently absent in the limb leads and is Rautaharju et al Standardization and Interpretation of the ECG, Part IV e245

most evident in leads V2 and V3, where its amplitude has been recognizing the onset of the QRS complex and the end of the suggested to be approximately 0.33 mV or 11% of the T T wave, (2) determining the appropriate lead(s) in which to wave.27 Its presence is heart-rate dependent; it is rarely measure the QT interval, and (3) adjusting the QT interval for present at rates greater than 95 bpm. Bradycardia enhances increases in QRS duration, gender, and rate. the U-wave amplitude and is present in 90% of cases at heart When the majority of ECGs were recorded on single- rates less than 65 complexes per minute.28 channel analog machines, various leads were recorded se- It has long been held that an increase in U-wave amplitude, quentially, and the QT interval was measured manually in the usually in association with depression of the ST segment and individual leads. Determination of the end of the T wave was a decrease in T-wave amplitude, may be caused by a variety often difficult and sometimes impossible, and the onset of the of cardioactive drugs with quinidine-like effects and by QRS complex and the end of the T wave varied in different hypokalemia and that with more advanced hypokalemia, that leads, appearing shorter when the axis of an individual lead is, K less than 2.7 mmol/L, the U-wave amplitude may was more perpendicular to the spatial vector of the onset of exceed the T-wave amplitude in the same lead. However, the QRS complex or the end of the T wave. The onset of the more recent information suggests that this may be due to QRS complex tends to occur up to 20 ms earlier in V2 and V3 fusion of the U wave with the T wave rather than to an than in the limb leads.35 Some regard differences of up to 50 increase in U-wave amplitude per se. ms in QT intervals measured in the various leads in normal Fusion of the U wave with the T wave also occurs in subjects as being normal36; others have suggested that differ- 29 37 Downloaded from association with an increase in sympathetic tone and in the ences of up to 65 ms were still within the limit of normal. presence of a markedly prolonged QT interval such as that This value is reported to be less in women than in men.38 which occurs in congenital and acquired long-QT syndromes When the QT interval is measured in individual leads, the (LQTS). lead showing the longest QT should be used.39 This is usually 30 An inverted U wave in leads V2 through V5 is abnormal. V2 or V3. However, if this measurement differs by more than It may appear transiently during acute ischemia or in the http://circ.ahajournals.org/ 40 ms from that in other leads, the measurement may be in 31,32 presence of hypertension. An abnormal U wave is often error, and measurements from adjacent leads should be quite subtle and is rarely an isolated ECG abnormality. Thus, considered. If the T wave and U wave are superimposed or its presence is often not recognized or is overlooked by ECG cannot be separated, it is recommended that the QT be readers and automated systems. For these reasons, no specific measured in the leads not showing U waves, often aVR and descriptive or diagnostic statements are recommended for aVL,39 or that the downslope of the T wave be extended by inclusion in the automated list of terms. It remains the drawing a tangent to the steepest proportion of the downslope responsibility of the overreader to recognize abnormal U until it crosses the TP segment. It should be recognized that by guest on October 18, 2017 waves and to determine their clinical relevance. defining the end of the T wave in these ways might under- Recommendation estimate the QT interval. 1 Statements concerning the U wave should be included in the As detailed in the section on ECG technology, most ECG interpretation when the U wave is inverted, when it is currently used automated digital machines record all leads merged with the T wave, or when its amplitude is greater than simultaneously. This technique permits their temporal align- that of the T wave. ment and superimposition, which facilitates a more accurate assessment of the beginning of the QRS complex, the end of The QT Interval the T wave, and the separation of the U wave from the T Measurement of the QT interval and its adjustment for rate, wave. As a result, the automatically measured QT interval is gender, and QRS prolongation represent 2 of the major often longer than the QT interval as measured in any challenges in electrocardiography. They are matters of great individual lead, and the values currently regarded as normal, importance to physicians, drug manufacturers, and regulatory which were established with single-channel sequential re- agencies because of the relationship between prolongation of cordings, may no longer be valid. Most automated systems do the QT interval and potentially lethal ventricular arrhythmias. not routinely display the superimposed tracings or the points The document released in October 2005 by the Food and used to derive the QT interval. Drug Administration (FDA) provides guidance for the design, In view of the clinical importance of the QT-interval conduct, analysis, and interpretation of clinical studies for prolongation, it is essential to visually validate QT-interval evaluation of QT-interval prolongation.33 prolongation reported by a computer algorithm. QT and ST-T patterns vary a great deal in various geno- In addition to administration of QT-prolonging cardioac- types of the LQTS. Zhang et al34 described 10 different ST-T tive drugs, a number of conditions can induce QT prolonga- patterns in first 3 genotypes of the syndrome (4 in LQT1, 4 in tion. It is often possible to identify a specific cause of QT LQT2, and 2 in LQT3), and these patterns were present in the prolongation when appropriate clinical information is avail- majority of genotyped LQTS patients. able; for instance, both hypokalemia and hypocalcemia can The QT interval is defined as the interval from the onset of prolong phase 2 and phase 3 of the action potential and the QRS complex, that is, the earliest indication of ventricular prolong the QT interval. It is not feasible here to compile a depolarization, to the end of the T wave, that is, the latest comprehensive list of all possible causes of QT prolongation. indication of ventricular repolarization. The problems asso- It is sufficient to emphasize that its presence in an ECG report ciated with this measurement include the following: (1) should call for a careful clinical evaluation of possible causes. e246 Circulation March 17, 2009

Recommendation particularly on the type of QT-adjustment function used. It is It is recommended that selective subsets of temporally important to recognize that normal limits established using aligned superimposed ECG leads be made available as an the upper and lower limits of actual percentile distributions of optional display to facilitate QT measurement and to validate the rate-adjusted QT are preferable to those as mean values the onset and end points of the QT interval. In view of the Ϯ2ϫSD because these distributions are strongly skewed.44 clinical importance of QT-interval prolongation, it is essential Normal standards for thresholds for abnormal QT from to visually validate QT-interval prolongation reported by a large subgroups of community-based populations are avail- computer algorithm. able.21,44–48 These limits are relatively uniform in reports that have appropriately used linear regression functions with QT- QT Correction for Rate rate adjustment as a linear or power function of RR or heart Many formulas have been proposed to adjust the QT interval rate.21,44,46–48 The following normal limits are suggested as a for rate.40,41 The most widely used is the formula derived by practical compromise for the evaluation of QT-interval pro- Bazett42 in 1920 from a graphic plot of measured QT intervals longation and shortening in adult men and women: prolonged in 39 young subjects. This adjustment procedure divides the QT: women, 460 ms or longer; men, longer than 450 ms; and measured QT by the square root of the RR interval to derive short QT: women and men, 390 ms or shorter. the rate-adjusted value. The formula introduced by Frideri- FDA guidelines for industry recommend that 3 severity cia,43 also in 1920, uses the cube root of RR. Bazett’s formula levels for rate-corrected QT be reported when considering leaves a strong positive residual correlation (rϭ0.32) and possible QT-prolonging effects of drugs: longer than 350 ms, Downloaded from Fridericia’s formula leaves a negative correlation (rϭϪ0.26 longer than 480 ms, and longer than 500 ms.32 to Ϫ0.32) with heart rate,44,45 and the adjusted QT values may Although the upper normal limits for QT adjusted for rate be substantially in error, particularly when the heart rate is as a linear function of RR in small groups of children high. More recently introduced formulas for QT adjustment stratified by age, gender, and heart rate have been pub- as a linear or power function of RR or heart rate for lished,52 the limits for prolonged and short QT established in http://circ.ahajournals.org/ adults44,45–48 and for children49 effectively remove the rate reasonably large groups of children have been reported only dependence of the adjusted QT, and they are clearly prefer- for Bazett’s formula.53 In that report, the 98th percentile limit able to both Bazett’s and Fridericia’s formulas. Some inves- for rate-adjusted QT was approximately 450 ms in children tigators have introduced separate normal limits or rate cor- younger than 12 years of age. The gender difference of 8 ms rection factors for each heart rate subinterval using the appeared in the 12- to 16-year age group. It should be noted so-called “bin method.”46,50 that QT adjusted by Bazett’s formula may produce false QT prolongations.45

by guest on October 18, 2017 Recommendation It is recommended that linear regression functions rather than Recommendation the Bazett’s formula be used for QT-rate correction and that It is recommended that, in addition to rate, an adjustment for the method used for rate correction be identified in ECG gender and age be incorporated into QT adjustment. As practical clinical limits for considering the QT interval as analysis reports. In addition, rate correction of the QT interval abnormal, it is recommended that the adjusted QT of 460 ms should not be attempted when RR interval variability is large, or longer in women and 450 ms or longer in men be as often occurs with atrial fibrillation, or when identification considered a prolonged QT interval and that QT 390 ms and of the end of the T wave is unreliable. shorter be considered a short QT interval. QT Correction for Gender and the Limits for Prolonged and Short QT Interval Correction for QRS Duration The QT interval prolongs in ventricular conduction defects, Although Bazett’s and Fridericia’s formulas make no adjust- and an adjustment for QRS duration becomes necessary.54–56 ment for gender, many studies have demonstrated that the QT This can be accomplished best by incorporating QRS dura- interval is longer in young and middle-aged females than in tion and RR interval as covariates into the QT-adjustment males. The gender difference is potentially important because formula or by using the JT interval (QT duration–QRS women are generally considered to be more prone to malig- duration).55 If the JT interval is chosen, normal standards nant arrhythmias in LQTS than men. The gender difference established specifically for the JT interval should be used.55 appears during adolescence,51 when the rate-adjusted QT shortens in boys, possibly as a testosterone effect, but Recommendation undergoes little change in girls. QT- and JT-adjustment formulas have recently been intro- The reported gender difference in various studies varies duced for use in the setting of prolonged ventricular conduc- from 6 to 10 ms in older age groups and from 12 to 15 ms in tion. With confirmation, they may be incorporated into younger adults. Overall, the gender difference in rate- automated algorithms to provide appropriate correction adjusted QT interval becomes small after 40 years of age and factors. practically disappears in older men and women. Separate gender- and age-specific QT-adjustment formulas have been Evaluation of QT Intervals in proposed to accommodate these differences.21,44,46,47 Normal Sequential Tracings limits proposed in different studies vary to a certain extent, Evaluation of QT intervals from sequential ECG recordings is depending on the characteristics of the study population and essential for identification of QT prolongation induced by Rautaharju et al Standardization and Interpretation of the ECG, Part IV e247

pharmacological agents in drug studies. It is also helpful as an The difference between the longest and shortest QT inter- adjunct to ST analysis in determining the presence of active vals is referred to as QT dispersion. This concept was ischemia in patients suspected of having myocardial introduced in 1990 for risk identification in patients with infarction. LQTS.61 Since its introduction, QT dispersion has been one When sequential tracings from patients recorded at differ- of the most popular topics in ECG research. In November ent times of day and at different locations are compared, it is 2006, a PubMed search cited 670 publications with QT important to recognize that the time of day can influence the dispersion in the title, and a Google search under “QT QT interval,57,58 that differences may exist between the dispersion measurement” revealed 171 000 communications. different recording systems and between the programs used The QT-dispersion concept has led to the expectation that for QT measurement, and that different formulas for QT-rate QT dispersion is a measure of regional or localized hetero- adjustment may have been used. Moreover, there is a signif- geneity of myocardial repolarization. Numerous studies have icant interreader variability in the measurement of QT inter- suggested an increased risk of morbidity and mortality for an val.59 Rigorous standardization of the recording and evalua- increase in QT dispersion. However, substantial methodolog- tion procedures should be followed when serial comparison ical problems with the QT-dispersion measurement have been of QT intervals is undertaken. identified that have raised fundamental questions about the The FDA guide for industry suggests that in the evaluation validity of the concept.62–65 In principle, the expectation that of possible QT prolongation induced by drugs, 2 levels of QT dispersion is a measure of the regional or localized change in serial ECGs in the rate-corrected QT from the Downloaded from heterogeneity of myocardial repolarization implies that the baseline be reported: an increase of greater than 30 ms and an leads with the shortest and longest QT contain signal infor- increase of greater than 60 ms.33 mation at the terminal part of the T wave that is not present Recommendation in the first 3 orthogonal components of the 12-lead ECG (or the composite global T wave).65 It is recommended that for serial comparisons ECG recorders http://circ.ahajournals.org/ meet specific performance standards and, if possible, be of Until adequately validated data in specific clinical condi- the same type; that uniform, carefully standardized ECG tions are presented showing that QT dispersion on the body acquisition and QT-measurement procedures be used; and surface ECG is the counterpart of localized dispersion of that, whenever possible, a single reader be responsible for myocardial repolarization and conveys adequately strong overreading sequential tracings of an individual patient or nondipolar signal information that cannot be extracted from research subject. the X,Y,Z components, it seems unwise to include it as a part of the routine ECG report.

by guest on October 18, 2017 QT Dispersion Increased heterogeneity of myocardial repolarization may pre- Recommendation dispose patients to the development of malignant ventricular It is recommended that QT dispersion not be included in arrhythmias.60 As indicated above, significant differences exist routine ECG reports. However, because of the fundamental in the duration of the QT interval when measured in the importance of the heterogeneity of myocardial repolarization individual leads. Visualization of these differences is facilitated in the genesis of malignant ventricular arrhythmias, continued by the display of a suitable subset of temporally aligned research into the identification of markers of increased simultaneous leads with a slight separation on the amplitude dispersion of myocardial repolarization on the body surface scale. ECG is encouraged. e248 Circulation March 17, 2009

Disclosures

Writing Group Disclosures

Other Research Speakers’ Ownership Consultant/Advisory Writing Group Member Employment Research Grant Support Bureau/Honoraria Interest Board Other James J. Bailey National Institutes of Health None None None None None None Rory Childers University of Chicago None None None None None None Barbara J. Deal Northwestern University None None None None None None Leonard S. Gettes University of North Carolina None None None None None None Anton Gorgels University Hospital None None None None None None Maastricht E. William Hancock Stanford University Medical None None None None Philips Medical None Center (retired Professor Systems†; Covance Emeritus) Diagnostics† Mark Josephson Harvard Medical Faculty None None None None Medtronic* None Physicians for Beth Israel Deaconess Medical Center Downloaded from Paul Kligfield Weill Medical College of None None None None Philips Medical*; None Cornell University Mortara Instrument*; GE Healthcare*; MDS Pharma Services†; Cardiac Science* http://circ.ahajournals.org/ Jan A. Kors Erasmus Medical Center None None None None None Welch Allyn* Peter Macfarlane University of Glasgow Cardiac Science None None None Cardiac Science None Corporation†; Corp†; Medtronic Medtronic Physio Control†; Physio Control†; Spacelabs Health Spacelabs Care†; Draeger Health Care†; Medical†; Draeger Heartlab†; by guest on October 18, 2017 Medical†; McKesson† Heartlab†; McKesson† Jay W. Mason Independent consultant None None None None None None David M. Mirvis University of Tennessee None None None None None None Peter Okin Weill Medical College of Merck & Co, None None None None None Cornell University Inc† Olle Pahlm BFC Klin None None None None None None Pentti M. Rautaharju Wake Forest University None None None None Philips Medical None Medical School (retired) Systems† Borys Surawicz CARE Group None None None None None None Gerard van Herpen Erasmus Medical Center None None None None None Welch Allyn* Galen S. Wagner Duke University Medical Medtronic† None None None None None Center Physiocontrol† Welch Allyn† Hein Wellens University of Maastricht None None None None Medtronic* None This table represents the relationships of writing group members that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all members of the writing group are required to complete and submit. A relationship is considered to be “significant” if (a) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (b) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant. Rautaharju et al Standardization and Interpretation of the ECG, Part IV e249

Reviewer Disclosures

Other Research Speakers’ Expert Ownership Consultant/Advisory Reviewer Employment Research Grant Support Bureau/Honoraria Witness Interest Board Other Jeffrey L. Intermountain Medical None None None None None None None Anderson Center Leonard S. Dreifus Hahnemann University None None None None None None None Hospital Mark Eisenberg McGill University None None None None None None None Nora Goldschlager University of None None None None None None None California, San Francisco Cindy Grines William Beaumont None None None None None None None Hospital Mark Hlatky Stanford University None None None None None None None Peter Kowey Lankenau Medical None None None None Cardionet† Transoma*; Cardionet†; None Office NewCardio*

Downloaded from Rachel Lampert Yale University Medtronic, Inc†; None None None None Medtronic* None Guidant/Boston Scientific†; St Jude† Robert Lichtenberg Heart Care Centers of None None None None None None None Illinois Jonathan Lindner Oregon Health and Genentech* None None None None Genentech*; None http://circ.ahajournals.org/ Sciences University VisualSonics* Frank Marcus University of Arizona None None None None None None None Robert J. University of Miami None None None None None None None Myerburg Gerald M. Pohost University of Southern None None None None None None None California, Keck School of Medicine

by guest on October 18, 2017 Richard Schofield University of Florida None None None None None None None Health Sciences Center Samuel Shubrooks Beth Israel Deaconess None None None None None None None Medical Center John Strobel IMA, Inc None None None None None None None Stuart A. Winston Michigan Heart, PC Medtronic*; Boston None Boston None None None None Scientific* Scientific* This table represents the relationships of reviewers that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all reviewers are required to complete and submit. A relationship is considered to be “significant” if (a) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (b) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant.

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KEY WORDS: AHA Scientific Statements Ⅲ electrocardiography Ⅲ 1920;7:35–70. electrophysiology Ⅲ ion channels Ⅲ long-QT syndrome AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part IV: The ST Segment, T and U Waves, and the QT Interval: A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: Endorsed by the International Society for Computerized Electrocardiology Downloaded from Pentti M. Rautaharju, Borys Surawicz and Leonard S. Gettes

Circulation. 2009;119:e241-e250; originally published online February 19, 2009;

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AHA/ACCF/HRS Scientific Statement

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram Part V: Electrocardiogram Changes Associated With Cardiac Chamber Hypertrophy A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology

E. William Hancock, MD, FACC; Barbara J. Deal, MD, FACC; David M. Mirvis, MD; Downloaded from Peter Okin, MD, FACC; Paul Kligfield, MD, FAHA, FACC; Leonard S. Gettes, MD, FAHA, FACC

he detection and assessment of cardiac chamber hyper- hypertrophy. It is doubtful whether enlargement occurs with- Ttrophy has long been an important objective of clinical out hypertrophy, at least in chronic stable syndromes. As electrocardiography. Its importance has increased in recent discussed below, distinctive P-wave abnormalities may occur http://circ.ahajournals.org/ years with the recognition that hypertrophy can be reversed in the absence of atrial hypertrophy or dilation.) with therapy, and that by doing so, adverse clinical outcomes The principal electrocardiogram (ECG) changes associated can be prevented or delayed.1,2 with ventricular hypertrophy are increases in QRS amplitude (Note: This report uses the term hypertrophy rather than and duration, changes in instantaneous and mean QRS enlargement. The 1978 Bethesda Conference favored use of vectors, abnormalities in the ST segment and T waves, and the term enlargement, but hypertrophy is more commonly abnormalities in the P wave. These changes have been used in recent research reports, although not necessarily in correlated with direct or indirect assessments of ventricular

by guest on October 18, 2017 textbooks. Enlargement may be taken to imply an increase in size or mass to establish electrocardiographic criteria for the chamber dimension, which may not be present in concentric diagnosis of hypertrophy.

Other members of the Standardization and Interpretation of the Electrocardiogram Writing Group include James J. Bailey, MD; Rory Childers, MD; Anton Gorgels, MD; Mark Josephson, MD, FACC, FHRS; Jan A. Kors, PhD; Peter Macfarlane, DSc; Jay W. Mason, MD, FAHA, FACC, FHRS; Olle Pahlm, MD, PhD; Pentti M. Rautaharju, MD, PhD; Borys Surawicz, MD, FAHA, FACC; Gerard van Herpen, MD, PhD; Galen S. Wagner, MD; and Hein Wellens, MD, FAHA, FACC. The American Heart Association, the American College of Cardiology, and the Heart Rhythm Society make every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest. Parts I and II of this series, “Recommendations for the Standardization and Interpretation of the Electrocardiogram,” were published in the March 13, 2007, issue of Circulation (Circulation. 2007;115:1306–1324 and 1325–1332). They are available online at http://circ.ahajournals.org/content/vol115/issue10/ Parts III, IV, V, and VI of this series are available online at http://circ.ahajournals.org/content/vol119/issue10/ (Circulation. 2009;119:e235–e240; e241–e250; e251–e261; and e262–e270). They also published ahead of print February 19, 2009. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on August 7, 2008, by the American College of Cardiology Board of Trustees on May 16, 2008, and by the Heart Rhythm Society on June 18, 2008. The American Heart Association requests that this document be cited as follows: Hancock EW, Deal BJ, Mirvis DM, Okin P, Kligfield P, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part V: electrocardiogram changes associated with cardiac chamber hypertrophy: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation. 2009;119:e251–e261. This article has been copublished in the Journal of the American College of Cardiology. Copies: This document is available on the World Wide Web sites of the American Heart Association (my.americanheart.org), the American College of Cardiology (www.acc.org), and the Heart Rhythm Society (www.hrsonline.org). A copy of the document is also available at http://www.americanheart. org/presenter.jhtml?identifierϭ3003999 by selecting either the “topic list” link or the “chronological list” link (No. LS-1888). To purchase additional reprints, call 843-216-2533 or e-mail [email protected]. Expert peer review of AHA Scientific Statements is conducted at the AHA National Center. For more on AHA statements and guidelines development, visit http://www.americanheart.org/presenter.jhtml?identifierϭ3023366. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.americanheart.org/presenter.jhtml? identifierϭ4431. A link to the “Permission Request Form” appears on the right side of the page. (Circulation. 2009;119:e251-e261.) © 2009 American Heart Association. Inc, American College of Cardiology Foundation, and the Heart Rhythm Society. Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.108.191097 e251 e252 Circulation March 17, 2009

Originally, measurement of ventricular mass at autopsy or other criteria. In a large group of patients with mild or the clinical features of the patients were the reference moderate hypertension, only 11.2% of patients with LVH by standards used to establish ECG criteria. Later, the ECG either the Cornell voltage criterion or the Sokolow-Lyon changes were referenced against findings from various imag- criterion had LVH diagnosed by both criteria.16 In addition, ing modalities such as chest radiography or left ventriculog- the various criteria have different positive and negative raphy. In recent years, 2-dimensional echocardiography has predictive values in different patient populations,17 suggest- become the favored reference standard, but it is now being ing that the value of multiple criteria may be additive. challenged by 3-dimensional echocardiography, computer- Published studies are currently insufficient to indicate whether ized tomography, and magnetic resonance imaging.3 Al- any of the more recently proposed criteria are clearly superior to though these newer imaging techniques provide a more the others or are simply redundant. The data do suggest that accurate assessment of ventricular myocardial mass than does interpretations should specify which criteria are used in making the ECG, they do not obviate the clinical use of the ECG. The a diagnosis and that automated systems should apply multiple greater convenience and lower cost of the ECG continue to criteria. Furthermore, because the accuracy of the criteria is support its widespread use for the diagnosis of ventricular empirical, that is, dependent on correlations between specific hypertrophy in clinical practice, epidemiological studies, and ECG measurements and a reference standard, only ECG criteria clinical trials. In addition, some ECG abnormalities have that have been formally tested should be used without modifi- been shown to have independent clinical prognostic value. cation from the tested form. One important issue in developing and applying diagnostic Downloaded from The evolution of these new methods provides a compelling reason to reassess the role of the ECG in detecting cardiac criteria for LVH based on QRS voltage is that QRS voltages hypertrophy and related abnormalities and to update our are influenced by a variety of factors other than left ventric- practice on the basis of new research findings and technolog- ular size or mass. These factors include age, gender, race, and ical developments. body habitus. Their effects may contribute to the limited accuracy of the ECG criteria. Day-to-day variability and http://circ.ahajournals.org/ Left Ventricular Hypertrophy variability resulting from variations in the sites of electrode placement also impact QRS voltages and, hence, the diag- Diagnostic Criteria Based on QRS Voltage nostic value of ECG voltage criteria. The most commonly used diagnostic criteria for left ventric- ular hypertrophy (LVH) are based on measurements of QRS Age voltages. The ECG criteria for LVH shown in Table 1 have Apart from the wide variation in the normal limits of QRS evolved over the years.65–78 Criteria were originally based on voltage in infants and children of various ages, there are important differences between adults of various ages, with QRS

by guest on October 18, 2017 R and S amplitudes in standard limb leads I and III, using clinical and autopsy data as reference standards.4–6 (Ampli- voltages tending to decline with increasing age. In general, the tudes of ECG complexes are referred to in millimeters, rather commonly used QRS voltage criteria apply to adults older than than millivolts. Using normal standardization, 10 mm equals 35 years.15 Standards for the 16- to 35-year age group are not as 1 mV; 1 mm equals 0.1 mV.) Many other voltage criteria well-established, and the diagnosis of LVH based on voltage were introduced after the general acceptance of the standard alone has a low accuracy in this age group. The diagnosis of 12-lead ECG, most notably by Sokolow and Lyon,7 who in 1949 LVH in highly trained athletes is especially problematic. introduced the widely used criterion based on the sum of SV1 and Gender RV5 or RV6. More recently, the sum of SV3 and RaVL, referred to as Adult women have a slightly lower upper limit of QRS the “Cornell voltage,” has been used.8 The point score of voltage than men do, although SV3 is the only measurement Romhilt and Estes, introduced in 1968, incorporates abnormal- with a large difference.18 The difference persists after adjust- ities in QRS axis and duration, QRS onset-to-peak time, and P ment for body size and cardiac mass. Some criteria have been and ST-T morphology, in addition to QRS amplitude.9 shown to improve their performance with gender adjustment, More recently, more complex criteria that are easily imple- but the adjustment is not the same for all criteria.8,13,18–20 mented with computerized recording and interpretation systems have been developed. These include indices based on products Race of voltage and QRS duration,10 computation of QRS area,11 Normal values of QRS voltages vary by race. African- composite use of several criteria,12 and indices based on scores Americans have a higher upper normal limit of QRS voltage derived from regression equations that incorporate multiple than do Euro-Americans, whereas Hispanic Americans have lower limits. In patients with mild or moderate hyperten- electrocardiographic and nonelectrocardiographic factors.13,14 The existence of many different criteria for diagnosing sion, the Sokolow-Lyon criterion has a higher sensitivity and lower specificity in African-Americans than in Euro- LVH makes clinical application more complex. The sensitiv- Americans, whereas the Cornell voltage criterion shows ity of the various criteria is generally quite low (usually less lower sensitivity and higher specificity in African-Americans than 50%), whereas the specificity is quite high (often in the than in Euro-Americans.19–23 range of 85% to 90%).15 However, the sensitivity and specificity of each criterion is different. Thus, the diagnostic Body Habitus accuracy will depend on the specific criterion used. Because Obesity is associated with increased left ventricular mass by of these differences in sensitivity and specificity, patients echocardiographic measurement but not with increased QRS who meet one set of criteria for LVH commonly do not meet voltage. This may be attributed to the insulating effect of Hancock et al Standardization and Interpretation of the ECG, Part V e253

Table 1. Criteria for Left Ventricular Hypertrophy

Amplitude First Author of Study Year of Study Publication Limb lead voltage (R I–S I)ϩ(S III–R III) Ͼ16 mm Lewis5 1914 RIϩS III Ͼ25 mm Gubner6 1943 RI Ͼ15 mm Gubner6 1943 R aVL Ͼ11 mm Sokolow7 1949 R aVF Ͼ20 mm Goldberger65 1949 QorSaVR Ͼ19 mm Schack73 1950 RϩS in any limb lead Ͼ19 mm Romhilt9 1968 Precordial lead voltage 76 SV1 Ͼ23 mm Wilson 1944 69 SV2 Ͼ25 mm Mazzoleni 1964 7 SV1ϩRV5 Ͼ35 mm Sokolow 1949 72 SV2ϩRV5,6 Ͼ45 mm Romhilt 1969 54 Downloaded from SV1,2ϩRV5,6 Ͼ35 mm Murphy 1984 66 SV1,2ϩRV6 Ͼ40 mm Grant 1957 RϩS any precordial lead Ͼ35 mm Grant66 1957 67 RV5:RV6 Ͼ1.0 Holt 1962 R, any precordial lead Ͼ26 mm McPhie70 1958 http://circ.ahajournals.org/ 77 SV2ϩRV4,5 Ͼ45 mm Wolff 1956 76 RV5 Ͼ33 mm Wilson 1944 76 RV6 Ͼ25 mm Wilson 1944 Combinations of limb and precordial voltage 68 RS aVFϩV2ϩV6 (Ͼ30 years) Ͼ59 mm Manning 1964 68 RS aVFϩV2ϩV6 (Ͻ30 years) Ͼ93 mm Manning 1964 SVϩR aVL (men) Ͼ28 mm Casale8 1985

by guest on October 18, 2017 3 8 SV3ϩR aVL (women) Ͼ20 mm Casale 1985 Total 12-lead voltage Ͼ175 mm Siegel74 1982 Combinations of voltage and nonvoltage Voltage-STT-LAA-axis-QRS duration Point score Romhilt9 1968 71 (R aVLϩSV3)ϫQRS duration Ͼ2436 mm/sec Molloy 1992 Total 12-lead voltageϫQRS duration Ͼ1742 mm/sec Molloy71 1992 Criteria for use with left anterior fascicular block 33 SV1ϩRV5ϩSV5 Ͼ25 Bozzi 1976 33 SV1,2ϩRV6ϩSV6 Ͼ25 Bozzi 1976 S IIIϩmax R/S any lead (men) Ͼ30 Gertsch32 1988 S IIIϩmax R/S any lead (women) Ͼ28 Gertsch32 1988 Criteria for use with right bundle-branch block Max R/S precordial lead (with LAD) Ͼ29 mm Vandenberg75 1991 75 SV1 Ͼ2 mm Vandenberg 1991 75 RV5,6 Ͼ15 mm Vandenberg 1991 S IIIϩmax R/S precordial (with LAD) Ͼ40 mm Vandenberg75 1991 RI Ͼ11 mm Vandenberg75 1991 Amplitudes are given in millimeters, where 1 mmϭ0.1 mV. LAD indicates .

adipose tissue and the greater distance from heart to the chest The Diagnostic Role of QRS Duration wall electrodes. The effect of obesity differs among the QRS duration is frequently increased in LVH. This is manifest various ECG criteria. In a study of patients with mild or by a diffuse increase in QRS duration or an increase in the time

moderate hypertension, the Cornell voltage-duration product from onset of QRS to the R-wave peak in V5 or V6. The was more often in the LVH range in obese patients than in the increased QRS duration may be attributed to the increased nonobese, whereas the Sokolow-Lyon criterion was less often thickness of the left ventricle wall and to intramural fibrosis, in the LVH range in obese patients.13,24–27 which distorts and prolongs transmural impulse propagation. e254 Circulation March 17, 2009

When the electrocardiographic pattern of LVH with wid- hypertrophy. Thus, this ECG finding, like others considered ened QRS is present, there may be loss of the septal Q wave, in this section, may be used to support a diagnosis of LVH often with a slurred R-wave upstroke. In these cases, it is rather than to make the diagnosis. reasonable to diagnose associated incomplete left bundle- branch block, an entity that is commonly seen only in the Prolonged QT Interval presence of LVH. A progression from LVH alone to incom- LVH is often associated with slight prolongation of the QT plete left bundle-branch block may be observed. interval, but it is not known whether QT-interval prolongation has independent value as an electrocardiographic criterion for ST-T Abnormalities With LVH LVH or is simply secondary to prolongation of QRS duration. The association of inverted T waves with increased work of A slightly prolonged QT interval is consistent with but not the left ventricle was described in 1929.28 The term “typical diagnostic of LVH. Such prolongation can reflect longer strain” was introduced in 194129 and referred to a specific transmembrane action potentials because of alterations in ion ST-T abnormality, which was attributed to an increased channels as part of the hypertrophic process. Further studies hemodynamic burden. It consisted of J-point depression, testing the added value of QT-interval, QRS-axis, and P-wave upwardly convex down-sloping depression of the ST seg- changes in identifying LVH may be worthwhile. ment, and asymmetrical inversion of the T wave. It is now appreciated that electrocardiographic LVH with ST-segment Diagnosis of LVH in the Presence of and T-wave abnormalities occurs in conditions that are not Intraventricular Conduction Defects Downloaded from necessarily caused by increased hemodynamic work, as in (Delays) and Bundle-Branch Block patients with dilated or hypertrophic cardiomyopathies, and Left ventricular hypertrophy commonly occurs in heart dis- that lesser degrees of ST-T abnormalities than the “typical eases that also cause intraventricular conduction defects or strain” pattern are associated with LVH. Thus, the terms delays (IVCDs). As both LVH and IVCDs alter QRS pat- “strain” and “typical strain” are discouraged, and the term terns, the existence of an IVCD may impact the accuracy of http://circ.ahajournals.org/ “secondary ST-T abnormalities” is preferred. The presence of ECG criteria for LVH. ST-T-wave abnormalities provides major support to a diag- Left Anterior Fascicular Block nosis of LVH that would otherwise be based only on In left anterior fascicular block, the QRS vector shifts in a increased QRS voltage, and there is evidence to suggest that posterior and superior direction, resulting in larger R waves in the presence of ST-T abnormalities are associated with larger leads I and aVL and smaller R waves but deeper S waves in values for left ventricular mass and higher risks of cardiovas- leads V5 and V6. R-wave amplitude in leads I and aVL are not cular complications and mortality than an increase in QRS reliable criteria for LVH in this situation. Criteria that include by guest on October 18, 2017 voltage alone.30,31 However, the evidence is insufficient to the depth of the S wave in left precordial leads improve indicate whether the “typical strain” pattern has more signif- detection of LVH in the presence of left anterior fascicular icant clinical implications than lesser ST-T abnormalities, block.32–34 whether ST-T abnormalities should be used to diagnose LVH in the absence of any QRS voltage criteria, or whether the Left Bundle-Branch Block presence of ST-T abnormalities should allow modification of Studies of the electrocardiographic diagnosis of LVH in the QRS voltage criteria. These are important issues for further presence of complete left bundle-branch block (LBBB) have investigation. yielded conflicting results.35–41 Some have concluded that the diagnosis should not be attempted in this setting,35–37 whereas Left Atrial Abnormalities With LVH others believe that the diagnosis can be made.38–41 Estima- P-wave abnormalities that are known to be associated with tions of specificity are affected by the relatively high preva- left atrial dilatation, hypertrophy, conduction delay, or ele- lence of anatomic LVH in patients with LBBB, especially in vated pressure are frequently associated with LVH and have autopsy series, where it may be 90% or more. The variable been used as diagnostic criteria. P-wave changes occur results may also reflect differing definitions of LBBB. Strict frequently in patients with hypertension, and they may be the definitions, which require monophasic notched or plateau- earliest electrocardiographic sign of hypertensive heart dis- topped R waves in leads I, aVL, V5, and V6, tend to show low ease. However, similar P-wave abnormalities often occur in sensitivity for LVH criteria.42 Broader definitions, which the absence of LVH. For this reason, and because adequate require only a QRS duration greater than 120 ms, slurred clinical studies assessing the accuracy of this criterion, either predominant R in left precordial leads, and slurred predomi- alone or in combination with other criteria, have not been nant S wave in the right precordial leads, probably include reported, P-wave abnormalities should only be used as a cases that could be classified as LVH with associated intra- supporting criterion. ventricular conduction delay rather than LBBB. Because “complete” LBBB may often be not truly complete, and Left Axis Deviation With LVH because the QRS duration in LVH can probably be greater Left axis deviation may be associated with LVH. However, it than 120 ms without a localized lesion in the left bundle, the is not known whether left axis deviation results from hyper- distinction between these two entities may be difficult to trophy itself, a degree of left anterior fascicular block, or define.43 A left atrial P-wave abnormality38,39,41 and a QRS other factors that may underlie the tendency toward a more duration greater than approximately 155 ms, as well as leftward axis with increasing age, even in the absence of precordial lead voltage criteria,35,38–42 tend to have relatively Hancock et al Standardization and Interpretation of the ECG, Part V e255

high specificity for LVH in the presence of LBBB. In patients normal voltage limits. When the higher sampling rates are meeting these specific criteria, it is reasonable to diagnose used, the amplitude criteria in children should be adjusted. LVH, even though the sensitivity is low. Otherwise, the ECG Gender and racial differences in QRS voltage similar to diagnosis of LVH should not be attempted when LBBB is those in adults exist in children older than 10 years. Adjust- present. ment for body habitus has not been adequately investigated. The sensitivity of ECG criteria for LVH is low in children, Right Bundle-Branch Block as it is in adults. The ECG is best used in pediatrics as a Right bundle-branch block (RBBB) reduces the amplitude of screening tool to be correlated with other measurements for the S wave in the right precordial leads and tends to reduce the assessment of hypertrophy. the sensitivity of electrocardiographic criteria for LVH. The ancillary features of left atrial abnormality and left axis Other Considerations deviation have enhanced value for the diagnosis of LVH in Several other factors influence the value of the ECG in the presence of RBBB.44–47 Several criteria have been pro- detecting LVH. The sensitivity and specificity of various posed for use specifically in the presence of RBBB, including ECG criteria reflect issues related to the types of heart SV1 greater than 2 mm (0.2 mV), RV5,6 greater than 15 mm (1.5 disease, anatomic patterns of LVH, and degrees of hypertro- mV), and QRS axis to the left of Ϫ30, with S IIIϩlargest R/S phy present in different patient populations. Okin et al16 noted in a precordial lead greater than 30 mm (3.0 mV). These that in patients with mild or moderate hypertension, an criteria were reported to have sensitivities of 46% to 68% and increase in the product of the SV3ϩRaVL voltage and the QRS Downloaded from specificities of 57% to 71%.47 duration characterized older patients who were obese and

female, whereas an increase in the sum of SV1 and RV5 was Issues of Terminology more characteristic of patients who were younger, male, Estimates of Probability black, and nonobese. The accuracy will also be different in Qualifying diagnostic terms such as probable or possible or populations in which LVH is unlikely (with most positive http://circ.ahajournals.org/ consider are subject to multiple interpretations and may be tests being false positives) than in populations in which LVH used to indicate that some criteria for LVH are met, but that is more likely, for example, groups of patients with signifi- the accuracy of these criteria is limited, or that the criteria cant hypertension, in which more negative results will be almost meet the threshold values, but that LVH is still false negatives. It is also important to recognize that the strongly considered because of other contravening variables, characteristics of patient groups in whom the criteria were such as obesity. Each interpretation has different meanings to established may be different from those in whom the criteria the reader and to the user of the ECG. Hence these terms are applied.

by guest on October 18, 2017 should be used and interpreted with caution. Additional studies would be worthwhile to propose specific criteria for Recommendations their use. 1. Interpretation of ECGs for LVH should use only vali- dated criteria, without deviation from the validated Diagnostic Terms formulas. Over years of use, electrocardiographers have adopted vari- 2. No single diagnostic criterion can be recommended for ous terms for certain ECG findings, many with limited use compared with the others. usefulness and accuracy. The terms systolic (pressure) over- 3. Computer systems should use all criteria that are sup- load and diastolic (volume) overload have limited accuracy in ported by valid evidence for identifying LVH. patients with congenital heart disease and in adults, and their 4. Interpretations should specify which diagnostic criteria use is not recommended. As discussed above, the term strain were used and which were abnormal (and thereby, by originated in an older concept of an ST-T abnormality that exclusion, which were examined but not found to be was considered to reflect ventricular overwork but not nec- abnormal). essarily hypertrophy. Its use should also be discontinued. 5. Criteria should be adjusted for factors known to alter accuracy, including gender, race, and body habitus, Special Issues in Children when such criteria have been validated. Electrocardiographic detection of ventricular hypertrophy in 6. The terms strain, systolic, and diastolic should not be children is largely based on QRS voltage abnormalities. The used in diagnostic statements related to LVH. standards for QRS voltage are derived from studies of 7. The terms probable, possible, and borderline should be populations of clinically normal children. Studies are rela- used with caution. tively few and do not always include referencing to body size, 8. Because the evidence is conflicting, the diagnosis of gender, or race. Correlation with echocardiograms is also LVH in the presence of complete LBBB should be limited, and reference standards from autopsy or magnetic made with caution. resonance imaging are not available. Standards derived from a population of Canadian chil- Recommendations for Further Study dren48 are widely used in North America. More recent studies Issues that require additional study before recommendations in Scottish children using a digital sampling rate of 500 can be made include the following: samples per second49 and in Dutch children using a sampling 1. Development and testing of adjustments of major diag- rate of 1200 samples per second50 showed higher upper- nostic criteria for gender, race, age, and body habitus; e256 Circulation March 17, 2009

2. Adjustment of major criteria for specific populations Table 2. Criteria for Right Ventricular Hypertrophy with varying prevalences of LVH, including (semi) First Author Year of Study quantitation of modifying terms such as possible and Amplitude of Study Publication probable; Tall R V Ͼ6 mm Myers78 1948 3. Development and testing of criteria for specific indica- 1 Ͼ 78 tions, for example, prognosis, screening, follow-up of Increased R:S ratio V1 1.0 Myers 1948 Ͼ 78 therapy, etc.; Deep S V5 10 mm Myers 1948 Ͼ 78 4. The added clinical value of the ECG when used in Deep S V6 3 mm Myers 1948 addition to other diagnostic methods; Tall R aVR Ͼ4 mm Sokolow7 1949 78 5. The possible use of ST-T abnormalities typical of LVH Small S V1 Ͻ2 mm Myers 1948 to diagnose LVH in cases where voltage criteria of LVH 78 Small R V5,6 Ͻ3 mm Myers 1948 are not met; 78 Reduced R:S ratio V5 Ͻ0.75 Myers 1948 6. The utility of voltage and other criteria, such as QRS Reduced R:S ratio V Ͻ0.4 Myers78 1948 axis, left atrial abnormality, and QRS duration, in 6 Ͻ 7 diagnosing LVH in the presence of LBBB; Reduced R:S V5 to R:S V1 0.04 Sokolow 1949 5 7. Identification of criteria that consistently outperform (R 1ϩS III)–(S IϩR III) Ͻ15 mm Lewis 1914 ϩ Ͼ 51 other criteria and those that are only redundant; MaxRV1,2 maxSI, 6 mm Butler 1986 8. For pediatric patients, possible improvement of criteria aVL–S V1 Downloaded from ϩ Ͼ 7 based on current sampling technology, wider demo- RV1 SV5,6 10.5 mm Sokolow 1949 78 graphic groups, and the use of more leads; and R peak V1 (QRS duration Ͼ0.035 sec Myers 1948 9. The effect of day-to-day variation of voltage and other Ͻ0.12 sec) 78 criteria on the validity of LVH criteria. QR V1 Present Myers 1948 Supporting criteria http://circ.ahajournals.org/

Right Ventricular Hypertrophy RSR V1 (QRS duration Present Right ventricular hypertrophy (RVH) causes a displacement Ͼ0.12 sec) of the QRS vector toward the right and anteriorly and often SϾR in I, II, III Present causes a delay in the R-wave peak in right precordial leads. S I and Q III Present However, considerable degrees of RVH are often required to R:S V ϾR:S V Present change the balance of right and left ventricular vectors, 1 3,4 because the vector of left ventricular activation dominates the Negative T-wave V1 Present through V3 by guest on October 18, 2017 balance in the normal heart and even more so in the setting of Ͼ LVH. Thus, the ability of the ECG to detect RVH may be P II amplitude 2.5 mm expected to be low. Amplitudes are given in millimeters, where 1 mmϭ0.1 mV. Numerous criteria mostly derived from the amplitude of R

and S in leads I, V1,V6, and the R-wave peak time in V1 have and T-wave inversion in right precordial leads; as with LVH, been proposed and are shown in Table 2. They have been these ST-T abnormalities are better referred to as “secondary correlated primarily with autopsy data, although some are ST-T abnormality” than as “strain.” In patients with chronic based on clinical and hemodynamic identification of condi- nonobstructive lung disease, there is often right axis deviation tions that impose increased workloads on the right ventri- and deep S waves in the precordial leads. 51–54 cle. The echocardiogram has also been used as a refer- Chronic obstructive pulmonary disease often causes a ence standard, but it is less definitive than in LVH because of characteristic electrocardiographic pattern that reflects the complex 3-dimensional shape of the right ventricle and mainly the low diaphragm resulting from the increased lung the frequent difficulty of measuring the thickness of the right volume. This pattern includes low voltage in the limb leads; ventricular free wall. a frontal plane QRS axis that is rightward, superior, or Although the sensitivity of the electrocardiographic criteria indeterminate; a rightward P-wave axis (ie, greater than 60 for RVH is generally low, some criteria have high specificity degrees); persistent S waves in all precordial leads; and low and can be used to advantage in diagnostic schemes or to R-wave amplitude in V .56 RVH is suggested, in the presence derive continuous variables.54,55 The greatest accuracy is in 6 congenital heart disease, with intermediate accuracy in ac- of the chronic obstructive pulmonary disease pattern, only if quired heart disease and primary pulmonary hypertension in R-wave amplitude in V1 is relatively increased. adults. The lowest accuracy occurs in chronic lung disease. Right axis deviation and prominent anterior forces in the Electrocardiographic RVH, particularly in congenital heart right precordial leads should be required for the electrocar- disease, has often been classified on the basis of contrasting diographic diagnosis of RVH in nearly all cases. On the other ECG patterns. One pattern is similar to that of incomplete hand, such features occur for various reasons other than RBBB, suggesting volume overload, and a second pattern RVH, including a not-infrequent normal variant. The use of consists of predominantly tall R waves (as part of Rs, R, or Qr ancillary clinical information, therefore, plays a greater role complexes) in right precordial leads, suggesting pressure in the appropriate use of the ECG for the purpose of overload. Both patterns are associated with right axis devia- recognizing RVH than it does in the case of LVH or the atrial tion. Both are also frequently associated with ST depression abnormalities. Hancock et al Standardization and Interpretation of the ECG, Part V e257

Table 3. Pediatric Criteria for Left Ventricular Hypertrophy Table 4. Pediatric Criteria for Right Ventricular Hypertrophy (Age-Related) (Age-Related)

Voltage (mm) Voltage (mm)

Age Age Age Age Age Age Age Age Age Age 0–7 d 7 d–1 y 1–3 y 3–5 y Ͼ5y 0–7 d 7 d–1 y 1–3 y 3–5 y Ͼ5y

RV6 Ͼ12 Ͼ23 Ͼ23 Ͼ25 Ͼ27 RV1 Ͼ27 Ͼ22 Ͼ18 Ͼ18 Ͼ13

SV1 Ͼ23 Ͼ18 Ͼ21 Ͼ22 Ͼ26 SV6 Ͼ10 Ͼ10 Ͼ7 Ͼ6 Ͼ4

SV1ϩRV6 Ͼ28 Ͼ35 Ͼ38 Ͼ42 Ͼ47 RV1ϩSV6 Ͼ37 Ͼ43 Ͼ30 Ͼ24 Ͼ17 Based on Davignon et al.48 Amplitudes are given in millimeters, where Based on Davignon et al.48 Amplitudes are given in millimeters, where 1mmϭ0.1 mV. 1mmϭ0.1 mV.

Recommendations tions caused similar abnormalities. However, other terms 1. No single criterion or limited set of criteria can be such as atrial hypertrophy, atrial overload, atrial strain, and recommended for use exclusive of other validated interatrial (or intraatrial) conduction defect have also been criteria. The effect of using larger numbers of criteria on used, reflecting the fact that atrial dilatation, atrial muscular sensitivity and specificity should be further studied. hypertrophy, elevated atrial pressure, impaired ventricular Downloaded from 2. Criteria should be adjusted for age, gender, race, and distensibility, and delayed intraatrial conduction all seem to body habitus. play a role in causing P-wave abnormalities. Because the 3. Probability estimates for RVH should be adjusted in the effects of these several factors on the P wave may often light of available clinical diagnoses suggesting congen- appear in combination and may not be distinguishable, the ital heart disease, , or chronic less specific terms left atrial abnormality and right atrial http://circ.ahajournals.org/ pulmonary disease. Incorporation of such clinical diag- abnormality are preferable. noses into computer algorithms should be explored. Left Atrial Abnormality Left atrial abnormality usually involves prolongation of the Biventricular Hypertrophy total atrial activation time, because left atrial activation Hypertrophy of both the right and left ventricle is relatively begins and ends later than right atrial activation. Delay in the common in patients with heart disease of many types. Its left atrial activation tends to cause a double-peaked or recognition by ECG has a particularly low sensitivity, ex- notched P wave, because the right and left atrial peaks that are by guest on October 18, 2017 plained at least in part by the cancellation of increased QRS normally nearly simultaneous and fused into a single peak vectors of both RVH and LVH. In the presence of ECG become more widely separated. Activation of the left atrium has a more leftward and posterior vector than that of the right criteria for LVH, the presence of prominent S waves in V5 or atrium. The product of the amplitude and the duration of the V6, right axis deviation, unusually tall biphasic R/S com- plexes in several leads, and signs of right atrial abnormality terminal negative component of the P wave in lead V1 (the P are useful signs that RVH may also be present.57,58 terminal force) has been used most frequently of the various In patients with congenital heart defects and RVH, the criteria for left atrial abnormality, but the P-wave duration presence of combined tall R waves and deep S waves in leads (120 ms or more) and widely notched P wave (40 ms or more) V to V , with combined amplitude greater than 60 mm (6.0 appear to have equal value. Several other criteria, including 2 4 Ϫ Ϫ mV), suggests the presence of LVH. left axis of the terminal P wave ( 30 to 90), and possibly the P-wave area, are also useful.59,60 A purely negative P Recommendations wave in V1 is suggestive but can occur without an increased 1. Biventricular hypertrophy should be suggested on the P terminal force. basis of the presence of accepted criteria for both RVH Prolonged activation time of the atrium, indicated by the and LVH. The low sensitivity of such patterns should be total duration of the P wave of 120 ms or more, is present noted. in a large majority of patients with electrocardiographic 2. Right axis deviation in the presence of electrocardio- signs that are considered to represent left atrial abnormal- graphic LVH and tall biphasic R/S complexes in several ities.61 Conduction delay is more closely linked to left leads should be recognized as suggestive of biventric- atrial abnormality than to right atrial abnormality, proba- ular hypertrophy. bly because it often represents delay in the specialized interatrial pathway (Bachmann’s bundle)62,63 and possibly within the left atrial myocardium as well. The more Atrial (P-Wave) Abnormalities general term intraatrial is therefore preferable to inter- Abnormalities in the P wave that are related to anatomic or atrial, even though the delay might in fact be primarily physiological abnormalities in the right or left atrium have interatrial. been recognized since the early years of electrocardiography. The terms P-mitrale, P-congenitale, and P-pulmonale were Right Atrial Abnormality later replaced by left atrial enlargement and right atrial Right atrial abnormality is typically manifested as an increase enlargement, as it was realized that different clinical condi- in amplitude of the P wave and a tendency to rightward shift e258 Circulation March 17, 2009

of the P-wave vector.64 A tall upright P wave in lead II Combined Atrial Abnormality (greater than 2.5 mm) is characteristic, often with a peaked or Combined atrial abnormality is indicated essentially by the pointed appearance that presumably reflects summation of presence of some of the features of both right atrial and left the enhanced right atrial component with the simultaneous atrial abnormality. However, little evidence is available left atrial component. Right atrial abnormality increases the regarding the accuracy of ECG criteria for combined atrial amplitude of the initial P-wave forces, contrasting with abnormality. increase in the later P-wave forces that can result from left atrial abnormality (pseudo-P pulmonale). Prominent initial Recommendations positivity of the P wave in V1 or V2 (1.5 mm [0.15 mV] or 1. Abnormal P waves should usually be referred to as right more) also indicates right atrial abnormality. Rightward axis or left “atrial abnormality” rather than enlargement, of the P wave and a peaked form without increased amplitude overload, strain, or hypertrophy. are supportive signs. Total P-wave duration is usually normal, 2. Multiple electrocardiographic criteria should be used to but an exception occurs in patients with surgically repaired recognize atrial abnormalities. congenital heart disease (especially those with single- 3. Intraatrial conduction delay should be recognized as a ventricle physiology) where significant P-wave prolongation category of atrial abnormality applicable particularly occurs and is a risk factor for the development of atrial to instances where P-wave widening is not accompanied tachyarrhythmias. by increased amplitude of right or left atrial components. Downloaded from

Disclosures

Writing Group Disclosures http://circ.ahajournals.org/ Other Research Speakers’ Ownership Consultant/Advisory Writing Group Member Employment Research Grant Support Bureau/Honoraria Interest Board Other James J. Bailey National Institutes of Health None None None None None None Rory Childers University of Chicago None None None None None None Barbara J. Deal Northwestern University None None None None None None Leonard S. Gettes University of North Carolina None None None None None None

by guest on October 18, 2017 Anton Gorgels University Hospital None None None None None None Maastricht E. William Hancock Stanford University Medical None None None None Philips Medical None Center (retired Professor Systems† Emeritus) Covance Diagnostics† Mark Josephson Harvard Medical Faculty None None None None Medtronic* None Physicians for Beth Israel Deaconess Medical Center Paul Kligfield Weill Medical College of None None None None Philips Medical*; None Cornell University Mortara Instrument*; GE Healthcare*; MDS Pharma Services†; Cardiac Science* Jan A. Kors Erasmus Medical Center None None None None None Welch Allyn* Peter Macfarlane University of Glasgow Cardiac Science None None None Cardiac Science None Corporation†; Corporation†; Medtronic Medtronic Physio Physio Control†; Control†; Spacelabs Spacelabs Health Health Care†; Care†; Draeger Draeger Medical†; Medical†; Heartlab†; Heartlab†; McKesson† McKesson† Jay W. Mason Independent Consultant None None None None None None David M. Mirvis University of Tennessee None None None None None None Peter Okin Weill Medical College of Merck & Co, None None None None None Cornell University Inc† (Continued) Hancock et al Standardization and Interpretation of the ECG, Part V e259

Writing Group Disclosures, Continued

Other Research Speakers’ Ownership Consultant/Advisory Writing Group Member Employment Research Grant Support Bureau/Honoraria Interest Board Other Olle Pahlm BFC Klin None None None None None None Pentti M. Rautaharju Wake Forest University None None None None Philips Medical None Medical School (retired) Systems† Borys Surawicz CARE Group None None None None None None Gerard van Herpen Erasmus Medical Center None None None None None Welch Allyn* Galen S. Wagner Duke University Medical Medtronic†; None None None None None Center Physiocontrol†; Welch Allyn† Hein Wellens University of Maastricht None None None None Medtronic* None This table represents the relationships of writing group members that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all members of the writing group are required to complete and submit. A relationship is considered to be “significant” if (a) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (b) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. Downloaded from †Significant. http://circ.ahajournals.org/ Reviewer Disclosures

Other Research Speakers’ Expert Ownership Consultant/Advisory Reviewer Employment Research Grant Support Bureau/Honoraria Witness Interest Board Other Jeffrey L. Intermountain Medical None None None None None None None Anderson Center Leonard Hahnemann University None None None None None None None by guest on October 18, 2017 S. Hospital Dreifus Mark McGill University None None None None None None None Eisenberg Nora University of None None None None None None None Goldschlager California, San Francisco Cindy William Beaumont None None None None None None None Grines Hospital Mark Stanford University None None None None None None None Hlatky Peter Lankenau Medical None None None None Cardionet† Transoma*; Cardionet†; None Kowey Office NewCardio* Rachel Yale University Medtronic, Inc†; None None None None Medtronic* None Lampert Guidant/Boston Scientific†; St. Jude† Robert Heart Care Centers of None None None None None None None Lichtenberg Illinois Jonathan Oregon Health and Genentech* None None None None Genentech*; None Lindner Sciences University VisualSonics* Frank University of Arizona None None None None None None None Marcus Robert J. University of Miami None None None None None None None Myerburg Gerald M. University of Southern None None None None None None None Pohost California, Keck School of Medicine (Continued) e260 Circulation March 17, 2009

Reviewer Disclosures, Continued

Other Research Speakers’ Expert Ownership Consultant/Advisory Reviewer Employment Research Grant Support Bureau/Honoraria Witness Interest Board Other Richard University of Florida None None None None None None None Schofield Health Sciences Center Samuel Beth Israel Deaconess None None None None None None None Shubrooks Medical Center John IMA, Inc None None None None None None None Strobel Stuart A. Michigan Heart, PC Medtronic*; None Boston None None None None Winston Boston Scientific* Scientific* This table represents the relationships of reviewers that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all reviewers are required to complete and submit. A relationship is considered to be “significant” if (a) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (b) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. Downloaded from †Significant.

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http://circ.ahajournals.org/ Circulation. 2009;119:e251-e261; originally published online February 19, 2009; doi: 10.1161/CIRCULATIONAHA.108.191097 Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231 Copyright © 2009 American Heart Association, Inc. All rights reserved. Print ISSN: 0009-7322. Online ISSN: 1524-4539 by guest on October 18, 2017

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AHA/ACCF/HRS Scientific Statement

AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram Part VI: Acute Ischemia/Infarction A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology

Galen S. Wagner, MD; Peter Macfarlane, DSc; Hein Wellens, MD, FAHA, FACC; Mark Josephson, MD, FACC, FHRS; Anton Gorgels, MD; David M. Mirvis, MD;

Downloaded from Olle Pahlm, MD, PhD; Borys Surawicz, MD, FAHA, FACC; Paul Kligfield, MD, FAHA, FACC; Rory Childers, MD; Leonard S. Gettes, MD, FAHA, FACC

his is the sixth and final section of the project to update in association with acute ischemia and infarction include Telectrocardiography (ECG) standards and interpretation. peaking of the T waves, referred to as hyperacute T-wave http://circ.ahajournals.org/ The project was initiated by the Council on Clinical Cardi- changes, ST-segment elevation and/or depression, changes ology of the American Heart Association (AHA). The ratio- in the QRS complex, and inverted T waves. nale for the project and the process for its implementation The ST-segment changes are produced by the flow of were described in a previous publication.1 currents, referred to as “injury currents,” that are generated by The ECG is considered the single most important initial the voltage gradients across the boundary between the ische- clinical test for diagnosing myocardial ischemia and infarction. mic and nonischemic myocardium during the resting and Its correct interpretation, particularly in the emergency depart- plateau phases of the ventricular action potential, which 2,3 by guest on October 18, 2017 ment, is usually the basis for immediate therapeutic interventions correspond to the TQ and ST segments of the ECG. Current and/or subsequent diagnostic tests. The ECG changes that occur guidelines suggest that when these ST-segment shifts reach

Other members of the Standardization and Interpretation of the Electrocardiogram Writing Group include James J. Bailey, MD; Barbara J. Deal, MD, FACC; Anton Gorgels, MD; E. William Hancock, MD, FACC; Jan A. Kors, PhD; Jay W. Mason, MD, FAHA, FACC, FHRS; Peter Okin, MD, FACC; Pentti M. Rautaharju, MD, PhD; and Gerard van Herpen, MD, PhD. The American Heart Association, the American College of Cardiology, and the Heart Rhythm Society make every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest. Parts I and II of this series, “Recommendations for the Standardization and Interpretation of the Electrocardiogram,” were published in the March 13, 2007, issue of Circulation (Circulation. 2007;115:1306–1324 and 1325–1332). They are available online at http://circ.ahajournals.org/content/vol115/issue10/ Parts III, IV, V, and VI of this series are available online at http://circ.ahajournals.org/content/vol119/issue10/ (Circulation. 2009;119:e235–e240; e241–e250; e251–e261; and e262–e270). They also published ahead of print February 19, 2009. This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on August 7, 2008, by the American College of Cardiology Board of Trustees on May 16, 2008, and by the Heart Rhythm Society on June 18, 2008. The American Heart Association requests that this document be cited as follows: Wagner GS, Macfarlane P, Wellens H, Josephson M, Gorgels A, Mirvis DM, Pahlm O, Surawicz B, Kligfield P, Childers R, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part VI: acute ischemia/infarction: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Circulation. 2009;119:e262–e270. This article has been copublished in the Journal of the American College of Cardiology. Copies: This document is available on the World Wide Web sites of the American Heart Association (my.americanheart.org), the American College of Cardiology (www.acc.org), and the Heart Rhythm Society (www.hrsonline.org). A copy of the document is also available at http://www. americanheart.org/presenter.jhtml?identifierϭ3003999 by selecting either the “topic list” link or the “chronological list” link (No. LS-1889). To purchase additional reprints, call 843-216-2533 or e-mail [email protected]. Expert peer review of AHA Scientific Statements is conducted at the AHA National Center. For more on AHA statements and guidelines development, visit http://www.americanheart.org/presenter.jhtml?identifierϭ3023366. Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at http://www.americanheart.org/presenter.jhtml? identifierϭ4431. A link to the “Permissions Request Form” appears on the right side of the page. (Circulation. 2009;119:e262-e270.) © 2009 American Heart Association, Inc, American College of Cardiology Foundation, and the Heart Rhythm Society. Circulation is available at http://circ.ahajournals.org DOI: 10.1161/CIRCULATIONAHA.108.191098 e262 Wagner et al Standardization and Interpretation of the ECG, Part VI e263

predetermined threshold values in 2 or more anatomically dedicated electrodes, 1 connected to the positive input of the contiguous body surface ECG leads, a diagnosis of acute ECG machine and the other to the negative input. The ischemia/infarction is indicated.4 When the ST segment is remaining 9 leads use only 1 dedicated positive electrode. elevated, the term ST-segment–elevation myocardial infarc- The negative electrode for the 6 chest leads (also referred to tion (STEMI) is used to describe the changes and to deter- as the precordial or V leads) is provided by Wilson’s central mine eligibility for acute reperfusion therapy. The STEMI terminal, which is composed of the averaged inputs from the designation is contrasted with that of NSTEMI (or non- right arm, left arm, and left leg electrodes. The negative STEMI), which includes all others, that is, those with lesser electrode for the 3 aV (or augmented) limb leads (aVR, aVL, amounts of ST-segment elevation, abnormal ST-segment and aVF) is provided by the averaged inputs from the 2 limb elevation in fewer than 2 contiguous leads, ST-segment electrodes that do not serve as the positive electrode for a depression, T-wave inversion, or no abnormalities at all. specified lead; for example, for aVR, the averaged potential The changes in the QRS complex reflect changes in of the left arm and left leg electrodes is used. electrical activation within the severely ischemic or infarcted A second principle is that the ST-segment elevation in any region.5 The magnitude and extent of these ECG changes lead will usually be associated with reciprocal ST-segment depend on the size and location of the ischemic/infarcted depression in leads whose positive pole is directed opposite to region and the relationship of this region to the spatial (ie, approximately 180° away from) the leads that show the orientation of the particular ECG lead. The size and location ST-segment elevation and vice versa. If no body surface lead of the affected region depend, in turn, on the coronary artery fulfills this condition, then only ST-segment elevation or Downloaded from involved, the site of occlusion within the artery, and the depression will be displayed on the routine 12-lead ECG. In presence or absence of collateral circulation. addition, reciprocal ST-segment change may be absent in With the advent of automated recording systems and the leads in which it would be expected if the voltage transmitted performance of large-scale, multicenter clinical trials, a large to the body surface is inadequate to meet diagnostic criteria. experience has accumulated that permits the redefinition of This might occur if, in addition to ischemia/infarction, there http://circ.ahajournals.org/ normal ECG characteristics and the correlation of ischemia- is associated left ventricular hypertrophy with ST- and induced ECG abnormalities to angiographic findings ob- T-wave changes, an intraventricular conduction disturbance tained in temporal proximity to the recording of the ECG. As with secondary ST- and T-wave changes, or pericarditis.7 For a result, the standard 12-lead body-surface ECG is now this reason, the injury currents associated with acute ische- capable of providing a more accurate correlation of the mia/infarction may cause ST-segment elevation, ST-segment waveform changes to the involved vessel and to the site of depression, both, or neither in any body surface lead depend- occlusion within that vessel. In addition, magnetic resonance ing on the relationship between the location of the positive

by guest on October 18, 2017 imaging studies that correlate the ECG changes that result and negative poles that determine the spatial orientation of from ischemia/infarction to the extent and location of the that lead, the location of the ischemic region, the magnitude of involved myocardial region are beginning to appear6 and are the voltage transmitted to the body surface, and the presence of expected to result in more anatomically valid nomenclature of confounding ECG abnormalities. For instance, ST-segment de- the ischemic/infarcted region, particularly in what is now pression in a lead with its positive pole to the left and superiorly referred to as the posterior region of the left ventricle. placed, such as lead aVL, is the reciprocal of and similar in The purpose of this section of the standards document is to meaning to ST-segment elevation in a lead with its positive pole reexamine the existing ECG criteria for ischemia/infarction. located to the right and inferiorly placed, such as lead III. Our recommendations are focused primarily on the changes Conversely, ST-segment depression in lead III is the reciprocal in the ST segment that occur during the early acute phase of of and similar in meaning to ST- segment elevation in lead aVL.

acute coronary syndromes; however, some of the T-wave In the same way, ST-segment depression in leads V1 and V2,in changes in the postreperfusion phase and the QRS changes in which the positive pole is located anteriorly, is the reciprocal of the chronic phase are also considered. The following topics and similar in meaning to the ST-segment elevation that would are discussed: (1) The meaning and importance of both ST- be recorded if the positive electrode were placed on the posterior

segment elevation and depression; (2) the concept of anatom- chest wall, as in the V8 and V9 positions. ically contiguous leads; (3) the threshold values for ST- It is important to recognize that the magnitude of ST- segment changes; (4) the use of the ST-segment spatial vector segment elevation and reciprocal ST-segment depression (or to determine the region involved and the occluded coronary vice versa) may not be identical because of differences in the artery; (5) the importance of postischemic T-wave changes; distance of the leads recording these changes from the (6) the diagnosis of ischemia/infarction in the presence of ischemic region and the deviation of the leads from being intraventricular conduction disturbances; and (7) quantitative 180° opposite to each other. This is particularly relevant to QRS changes for estimation of chronic infarct size. the ST-segment changes that occur in lead aVL, because this lead frequently has a spatial orientation that is approximately Meaning and Importance of ST-Segment perpendicular to the mean QRS vector. Elevation and Depression It is also important to stress that factors other than acute An understanding of the relationship between ST-segment ischemia may cause elevation or depression of the ST elevation and depression requires consideration of certain segment. Factors that may cause ST-segment depression bioelectric principles. One of these is that all leads are include but are not limited to hypertrophy, cardioactive drugs, bipolar. However, only 3 leads (leads I, II, and III) use 2 and lowered serum potassium. Factors that may cause ST- e264 Circulation March 17, 2009

segment elevation include but are not limited to pericarditis, recommended in the 2000 European Society of Cardiology/ elevated serum potassium, Osborne waves, acute myocarditis, American College of Cardiology guidelines4 for universal certain cardiac tumors, and the normal variant referred to as adoption in 12-lead electrocardiography. early repolarization. Criteria have been published to differ- entiate these abnormalities in the ST segment from those Recommendation associated with acute ischemia.7 1. ECG machines should be equipped with switching systems Acute ischemia that typically results from coronary artery that will allow the limb leads to be displayed and labeled occlusion is associated with ST-segment elevation in leads appropriately in their anatomically contiguous sequence. whose positive poles are located over the ischemic region and with reciprocal ST depression in leads whose positive poles Threshold Values for ST-Segment Changes are oriented in the opposite direction. It is anatomically The threshold values of ST-segment elevation of 0.2 mV reasonable but conceptually limiting to refer to leads as (2 mm) in some leads and 0.1 mV (1 mm) in others results anterior, inferior,orlateral, because this nomenclature refers from recognition that some elevation of the junction of the only to the location on the body surface of the electrode that QRS complex and the ST segment (the J point) in most chest determines the positive pole of that lead. These lead descrip- leads is normal. Recent studies have revealed that the thresh- tions, although frequently used, may mislead clinicians to old values are dependent on gender, age, and ECG lead.8–12 In consider that all ST-segment abnormalities in a particular healthy individuals, the amplitude of the ST junction is

lead, for example, an anterior lead such as V1 or V2, are generally highest in leads V2 and V3 and is greater in men Downloaded from located in that anatomic region and could not be the recipro- than in women. cal of ischemic ST-segment changes occurring in the opposite anatomic region. Indeed, depression of the ST segment in Recommendations

leads V1 and V2 is a common manifestation of a posterior or 1. For men 40 years of age and older, the threshold value for lateral ST-segment elevation infarction. Note that the concept abnormal J-point elevation should be 0.2 mV (2 mm) in http://circ.ahajournals.org/ of subendocardial ischemia causing depression of the ST leads V2 and V3 and 0.1 mV (1 mm) in all other leads. segment in multiple leads is still tenable and, as discussed 2. For men less than 40 years of age, the threshold values for below, may be thought of as the reciprocal of endocardial ST- abnormal J-point elevation in leads V2 and V3 should be segment elevation caused by currents of injury directed 0.25 mV (2.5 mm). 3. For women, the threshold value for abnormal J-point eleva- toward the ventricular chamber. tion should be 0.15 mV (1.5 mm) in leads V2 and V3 and greater than 0.1 mV (1 mm) in all other leads. Recommendation 4. For men and women, the threshold for abnormal J-point

by guest on October 18, 2017 1. Labeling specific leads as anterior, inferior, and lateral elevation in V3R and V4R should be 0.05 mV (0.5 mm), should be avoided. Leads should be identified according to except for males less than 30 years of age, for whom 0.1 their original nomenclature, that is, leads I, II, III, aVR, mV (1 mm) is more appropriate. aVL, aVF, and V1 through V6. This recommendation refers 5. For men and women, the threshold value for abnormal J- only to the labeling of the leads. Reference to the anatomic point elevation in V through V should be 0.05 mV location of the ischemic/infarcted region, such as anterior 7 9 (0.5 mm). or inferior, is still recommended and is based on the leads 6. For men and women of all ages, the threshold value for that show the ST-segment alterations. This is discussed abnormal J-point depression should be Ϫ0.05 mV below. (Ϫ0.5 mm) in leads V2 and V3 and Ϫ0.1 mV (Ϫ1 mm) in Concept of Anatomically Contiguous Leads all other leads. The current ECG standards for diagnosing acute ischemia/ Correlation of ST-Segment Elevation and infarction require that ST-segment elevation be present in 2 or more contiguous leads and that the elevation of the ST Depression to the Region Involved and to the segment at the J point be greater than 0.2 mV (2 mm with Occluded Vessel It is currently proposed that the diagnosis of acute ischemia/ standard calibration) in leads V1,V2, and V3 and greater than 0.1 mV in all other leads.4 In the classic ECG display, the infarction be based on the presence of ST elevation, as measured at the J point,4 equaling or exceeding the thresholds chest leads V1 through V6 are displayed on the ECG paper in defined above in 2 or more anatomically contiguous leads. their anatomically contiguous order from right anterior (V1) The affected region is identified by the position on the body to left lateral (V6); however, the limb leads are not. Rather, they are displayed in 2 groups of 3: leads I, II, and III and surface of the leads that reveal the ST-segment elevation. The leads aVR, aVL, and aVF, which reflects their historical more precise the localization of the spatial vector of the ST- development. For these leads to be displayed in their anatom- segment shift, as determined from analysis of leads with ST- ically contiguous manner, that is, from left superior-basal to segment depression and ST-segment elevation, the more right inferior, the display should be aVL, I, ϪaVR (ie, lead robust will be the localization of the ischemic/infarcted aVR with reversed polarity), II, aVF, and III. With this region. The correlation of these ST-segment changes to the configuration, ϪaVR exists at 30° in the hexaxial frontal results of coronary angiography performed in temporal prox- plane, ie, midway between limb lead I (at 0°) and limb lead imity has permitted the more accurate identification of the II (at 60°). This display, known as the Cabrera format, has obstructed coronary artery and the proximal or distal location been the existing standard in Sweden for 25 years and was of the obstruction within that artery. These correlations have Wagner et al Standardization and Interpretation of the ECG, Part VI e265

7,13–15 been detailed in several publications and are reviewed 4. When ST-segment elevation is present in leads V3 through below. V6, and ST-segment depression is not present in leads II, Anterior wall ischemia/infarction is invariably due to III, and aVF, the automated interpretation should suggest occlusion of the left anterior descending coronary artery and anterior wall ischemia/infarction due to occlusion of the results in the spatial vector of the ST segment being directed mid or distal portion of the left anterior descending coronary artery. to the left and laterally. This will be expressed as ST elevation in some or all of leads V1 through V6. The location of the Inferior wall infarction that results in ST-segment elevation occlusion within the left anterior descending coronary artery, in only leads II, III, and aVF may be the result of occlusion that is, whether proximal or distal, is suggested by the chest of either the right coronary artery (RCA) or the left circum- leads in which the ST-segment elevation occurs and the flex coronary artery (LCx), depending on which provides the presence of ST-segment elevation or depression in other posterior descending branch, that is, which is the dominant leads. vessel. When the RCA is occluded, the spatial vector of the Occlusion of the proximal left anterior descending coro- ST segment will usually be directed more to the right than nary artery above the first septal and first diagonal branches when the LCx is occluded. This will result in greater ST- results in involvement of the basal portion of the left segment elevation in lead III than in lead II and will often be ventricle, as well as the anterior and lateral walls and the associated with ST-segment depression in leads I and aVL, interventricular septum. This will result in the ST-segment leads in which the positive poles are oriented to the left and Downloaded from spatial vector being directed superiorly and to the left and will superiorly.17,18 When the RCA is occluded in its proximal be associated with ST-segment elevation in leads V1 through portion, ischemia/infarction of the right ventricle may occur, V4, I, aVL, and often aVR. It will also be associated with which causes the spatial vector of the ST-segment shift to be reciprocal ST-segment depression in the leads whose positive directed to the right and anteriorly, as well as inferiorly. This poles are positioned inferiorly, that is, leads II, III, aVF, and will result in ST-segment elevation in leads placed on the 15,16 http://circ.ahajournals.org/ often V . Typically, there will be more ST elevation in 5 right anterior chest, in positions referred to as V3R and V4R, aVL than in aVR and more ST-segment depression in lead III 19–21 and often in lead V1. Lead V4R is the most commonly than in lead II, because the ST-segment spatial vector will be used right-sided chest lead. It is of great value in diagnosing directed more to the left than to the right. right ventricular involvement in the setting of an inferior wall When the occlusion is located between the first septal and infarction and in making the distinction between RCA and first diagonal branches, the basal interventricular septum will LCx occlusion and between proximal and distal RCA occlu- be spared, and the ST segment in lead V1 will not be elevated. sion. It is important to recognize that the ST elevation in the In that situation, the ST-segment vector will be directed

by guest on October 18, 2017 right-sided chest leads associated with right ventricular in- toward aVL, which will be elevated, and away from the farction persists for a much shorter period of time than the ST positive pole of lead III, which will show depression of the elevation connoting inferior wall infarction that occurs in the 14 ST segment. When the occlusion is located more distally, extremity leads. For this reason, leads V3R and V4R should be that is, below both the first septal and first diagonal branches, the recorded as rapidly as possible after the onset of chest pain.14 basal portion of the left ventricle will not be involved, and the The joint task force of the AHA and the American College of ST-segment vector will be oriented more inferiorly. Thus, the ST Cardiology, in collaboration with the Canadian Cardiovascu- segment will not be elevated in leads V1, aVR, or aVL, and the lar Society, has recommended that right-sided chest leads

ST segment will not be depressed in leads II, III, or aVF. Indeed, V3R and V4R be recorded in all patients presenting with ECG because of the inferior orientation of the ST-segment vector, evidence of acute inferior wall ischemia/infarction.22 elevation of the ST segment in leads II, III, and aVF may occur. In addition, ST-segment elevation may be more prominent in Recommendations

leads V3 through V6 and less prominent in V2 than in the more 1. ECG machines should be programmed to suggest the proximal occlusions.16 recording of the right-sided chest leads V3R and V4R when ST elevation greater than 0.1 mV occurs in leads II, III, and Recommendations aVF. 2. ECG machines should be equipped with a mechanism to 1. ECG manufacturers are encouraged to develop software label leads V R and V R. capable of displaying the spatial orientation of the ST- 3 4 3. Descriptive and interpretative statements should be devel- segment vector in both the frontal and transverse planes. oped to describe and interpret abnormalities that might 2. Wherever possible, the ECG diagnosis provided by automated occur in leads V R and V R. algorithms should refer to the occluded vessel and to the 3 4 site of the occlusion within that vessel, as well as to the ST-segment depression in leads V ,V, and V that occurs region involved. 1 2 3 in association with an inferior wall infarction may be caused 3. When ST-segment elevation is present in I and aVL, as by occlusion of either the RCA or the LCx. This ECG pattern well as in leads V1 through V4 and sometimes in V6, and ST-segment depression is present in leads II, III, and aVF, has been termed posterior or posterolateral ischemia since the automated interpretation should suggest an extensive the recommendations of Perloff23 and Horan et al24 and is anterior wall or anterobasal ischemia/infarction due to based on anatomic and pathological studies of ex vivo hearts. occlusion of the proximal portion of the left anterior However, recent in vivo imaging techniques, including echo- descending coronary artery. cardiography and magnetic resonance imaging, have demon- e266 Circulation March 17, 2009

strated the oblique position of the heart within the thorax. segment depression may be localized to specific leads such as

These studies demonstrated that the region referred to as the V2 and V3, and in this situation, there will not be ST elevation posterior wall was lateral rather than posterior and led to the on the 12-lead ECG because no body surface leads are suggestion that the term posterior be replaced by the desig- routinely placed opposite to these leads. nation lateral.25 Bayés de Luna et al6 correlated the ECG ST-segment elevation in more than 1 discrete region is patterns of healed myocardial infarctions to their anatomic characteristic of pericarditis involving large portions of the location as determined by magnetic resonance imaging. They epicardial surface.7 ST-segment depression in more than 1 reported that the most frequent cause of abnormally tall and discrete region that occurs in the absence of ST-segment

broad R waves in leads V1 and V2 in patients known to have elevation in leads I, II III, aVL, and V2 through V6 implies the experienced a recent acute infarction was involvement of the presence of currents of injury directed away from the body lateral and not the posterior wall of the left ventricle. They surface and toward the ventricular chamber and may indicate suggested that the terms posterior ischemia and posterior the presence of ischemia in more than 1 region of the heart.

infarction be replaced by the terms lateral, inferolateral,or In these situations, leads aVR and V1, in which the positive basal-lateral depending on the associated changes in II, III, poles are located to the right, superiorly and anteriorly, may

aVF, V1,V5, and V6. Such terminology has been endorsed by reveal ST elevation that reflects the spatial vector of the the International Society for Holter and Noninvasive injury currents. Such diffuse ST-segment depression usually Electrocardiography.26 implies nontransmural ischemia or injury and is characteristic

Downloaded from of 2 situations. The first is in association with stable angina Recommendation pectoris and can be brought about by treadmill or bicycle 1. It is the opinion of the committee that for the present, and exercise and other forms of stress. This is usually associated not withstanding the recommendation of the International with subtotal occlusion of 1 or more coronary arteries and Society for Holter and Noninvasive Electrocardiography, occurs when the oxygen demand of the myocardium is the current ECG terminology of posterior be retained to increased beyond the ability of coronary flow to meet this http://circ.ahajournals.org/ describe ST depression in leads V1 and V2 and the subsequent development of broad R waves in these leads, increased demand. Identification of the obstructed coronary as described in the previously published section concerning artery or arteries on the basis of the ST-segment change is not terminology.27 Further collaborative studies involving possible in this setting. larger groups of patients having a variety of ages and body In the second situation, ST depression in multiple leads builds and having acute ischemia as well as established occurs at rest in patients with pectoris. This is infarctions are recommended to provide further data on this frequently associated with severe multivessel or left main topic. This recommendation, as well as the others in this coronary artery stenosis.29 It has been reported that in patients by guest on October 18, 2017 report, will be reviewed periodically to determine whether with angina at rest, ST-segment depression in 8 or more body changes should be recommended. surface ECG leads, combined with ST elevation in aVR and V , is associated with a 75% predictive accuracy of 3-vessel It is not possible to determine whether the RCA or LCx 1 or left main stenosis.14 vessel is occluded when changes of inferior wall ischemia/ infarction are accompanied by depression of the ST segment Recommendation in leads V ,V, and V ; however, the absence of such changes 1 2 3 1. When the resting ECG reveals ST-segment depression greater is more suggestive of RCA than LCx occlusion. When the than 0.1 mV (1 mm) in 8 or more body surface leads coupled LCx is occluded, the spatial vector of the ST segment in the with ST-segment elevation in aVR and/or V1 but is otherwise frontal plane is more likely to be directed to the left than when unremarkable, the automated interpretation should suggest the RCA is occluded. For this reason, the ST segment may be ischemia due to multivessel or left main coronary artery elevated to a greater extent in lead II than in lead III and may obstruction. be isoelectric or elevated in leads 1 and aVL.28 When a dominant RCA is occluded proximally, left posterolateral and Postischemic T-Wave Changes right ventricular wall involvement will be present, and the Often, after ischemia and infarction, T waves become in- posteriorly directed ST-segment vector associated with this verted in leads with previous ST-segment elevation and

involvement may cancel the ST-segment elevation in lead V1 remain inverted for varying periods that range from days to anticipated by right ventricular involvement and vice versa. permanently. There is an important subgroup of patients in We have stated above that ST depression is always the whom deeply inverted T waves, that is, greater than 0.5 mV,

reciprocal of ST-segment elevation in leads located opposite occur in leads V2,V3, and V4, and occasionally V5, often with to the body surface leads recording the ST depression; significant QT prolongation, after an episode of chest pain but however, in some cases, only ST elevation or depression (but without further ECG evidence of evolving infarction or not both) will be present on the routine 12-lead ECG. For ongoing ischemia. This ECG pattern is similar to that which instance, when ST elevation is localized to leads with positive may occur after an intracranial hemorrhage (the CVA [cere- poles that overlie a particular anatomic region, such as the brovascular accident] pattern) and in some forms of cardio- 7 midanterior left ventricular walls (eg, V3 through V6), there myopathy. Coronary angiography in this subgroup of pa- may not be reciprocal ST-segment depression on the body tients usually reveals severe stenosis of the proximal left surface ECG because no body surface leads are routinely anterior descending coronary artery with collateral circula- 30,31 placed opposite to leads V3 through V6. In some cases, ST- tion. If these changes are not recognized and the patients Wagner et al Standardization and Interpretation of the ECG, Part VI e267

are not evaluated and treated appropriately, a high percentage had very low specificity and sensitivity. It also reported that may experience an acute anterior wall infarction, with the the presence of left bundle-branch block with concordant ST- risks associated with occlusion of the proximal left anterior segment changes was associated with a higher 30-day mor- descending coronary artery.32 tality than associated with left bundle-branch block and an enzyme rise but without concordant ST-segment changes. Recommendation 1. The specific pattern of deeply inverted T waves with QT Recommendation

prolongation in leads V2 through V4 should be interpreted as 1. Automated ECG algorithms should suggest the possibility of consistent with severe stenosis of the proximal left anterior acute ischemia/infarction in patients with left bundle-branch descending coronary artery or with a recent intracranial block who have ST-segment changes that meet the above hemorrhage (CVA [cerebrovascular accident] pattern). criteria. Diagnosis of Ischemia/Infarction in the Setting Quantitative QRS Changes for Estimation of of Intraventricular Conduction Disturbances Infarct Size ST-segment criteria for the diagnosis of acute ischemia/ One method for determining the presence of a remote myocar- infarction are not affected by the presence of fascicular blocks dial infarct has been the Minnesota Code.36 This method was or by right bundle-branch block. They are affected by the developed for the diagnosis of infarction rather than the quanti- presence of left bundle-branch block because of the more fication of its size and correlates poorly with anatomically 37 Downloaded from pronounced secondary ST- and T-wave changes that occur in measured infarct size. An improved correlation of changes in this setting. Criteria for infarction in the presence of complete the QRS complex with infarct size was the development of a left bundle-branch block have been published33 based on a QRS scoring system by Selvester et al using a computer model retrospective analysis of patients enrolled in the GUSTO of the human myocardial activation sequence reported by Durrer et al.38 The Selvester QRS scoring system included 54 weighted (Global Utilization of Streptokinase and Tissues plasminogen criteria from the QRS complexes in 10 of the standard leads http://circ.ahajournals.org/ activator for Occluded coronary arteries) I trial. These include (leads I, II, aVL, aVF, and V throughV ), which totaled 32 QRS ST-segment elevation greater than or equal to 0.1 mV (1 mm) 1 6 points, each equivalent to approximately 3% of the left ventric- in leads with a positive QRS complex and ST depression ular wall.39 The specificity of the Selvester method has been greater than or equal to 0.1 mV (1 mm) in leads V through 1 established in normal subjects, and its ability to detect and V , ie, leads with a dominant S wave. These are referred to as 3 estimate the anatomically determined sizes of prior infarctions concordant ST-segment changes. A third criterion is ST- has been documented.40 However, these estimates are most segment elevation greater than or equal to 0.5 mV (5 mm) in useful in the setting of a single infarct.

by guest on October 18, 2017 leads with a negative QRS complex. These are referred to as discordant ST-segment changes. Concordant ST-segment Recommendation changes and ST depression in leads V1 through V3 have been 1. Algorithms capable of determining the Selvester score in reported to demonstrate high specificity but low sensitivity,33,34 and tracings that meet the criteria for prior infarctions should be the most recent study35 reported that discordant ST changes developed and available for use by the reader if so desired. e268 Circulation March 17, 2009

Disclosures

Writing Group Disclosures

Other Speakers’ Writing Group Research Bureau/ Ownership Consultant/Advisory Member Employment Research Grant Support Honoraria Interest Board Other James J. Bailey National Institutes of None None None None None None Health Rory Childers University of Chicago None None None None None None Barbara J. Deal Northwestern University None None None None None None Leonard S. Gettes University of North Carolina None None None None None None Anton Gorgels University Hospital None None None None None None Maastricht E. William Stanford University Medical None None None None Philips Medical None Hancock Center (retired Professor Systems†; Covance Emeritus) Diagnostics† Mark Josephson Harvard Medical Faculty None None None None Medtronic* None

Downloaded from Physicians for Beth Israel Deaconess Medical Center

Paul Kligfield Weill Medical College of None None None None Philips Medical*; None Cornell University Mortara Instrument*; GE http://circ.ahajournals.org/ Healthcare*; MDS Pharma Services†; Cardiac Science* Jan A. Kors Erasmus Medical Center None None None None None Welch Allyn* Peter Macfarlane University of Glasgow Cardiac Science Corp†; None None None Cardiac Science None Medtronic Physio Corp†; Medtronic Control†; Spacelabs Physio Control†; Health Care†; Draeger Spacelabs Health by guest on October 18, 2017 Medical†; Heartlab†; Care†; Draeger McKesson† Medical†; Heartlab†; McKesson† Jay W. Mason Independent Consultant None None None None None None David M. Mirvis University of Tennessee None None None None None None Peter Okin Weill Medical College of Merck & Co, Inc† None None None None None Cornell University Olle Pahlm BFC Klin None None None None None None Pentti M. Wake Forest University None None None None Philips Medical None Rautaharju Medical School (retired) Systems† Borys Surawicz CARE Group None None None None None None Gerard van Herpen Erasmus Medical Center None None None None None Welch Allyn* Galen S. Wagner Duke University Medical Medtronic†; None None None None None Center Physiocontrol†; Welch Allyn† Hein Wellens University of Maastricht None None None None Medtronic* None This table represents the relationships of writing group members that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all members of the writing group are required to complete and submit. A relationship is considered to be “significant” if (1) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (2) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant. Wagner et al Standardization and Interpretation of the ECG, Part VI e269

Reviewer Disclosures

Other Speakers’ Research Research Bureau/ Expert Ownership Consultant/Advisory Reviewer Employment Grant Support Honoraria Witness Interest Board Other Jeffrey L. Intermountain Medical None None None None None None None Anderson Center Leonard S. Dreifus Hahnemann University None None None None None None None Hospital Mark Eisenberg McGill University None None None None None None None Nora Goldschlager University of None None None None None None None California, San Francisco Cindy Grines William Beaumont None None None None None None None Hospital Mark Hlatky Stanford University None None None None None None None Peter Kowey Lankenau Medical None None None None CardioNet† Transoma*; CardioNet†; None Office NewCardio*

Downloaded from Rachel Lampert Yale University Medtronic†; None None None None Medtronic* None Guidant/Boston Scientific†; St. Jude† Robert Lichtenberg Heart Care Centers of None None None None None None None Illinois http://circ.ahajournals.org/ Jonathan Lindner Oregon Health and Genentech* None None None None Genentech*; None Sciences University VisualSonics* Frank Marcus University of Arizona None None None None None None None Robert J. University of Miami None None None None None None None Myerburg Gerald M. Pohost University of Southern None None None None None None None California, Keck

by guest on October 18, 2017 School of Medicine Richard Schofield University of Florida None None None None None None None Health Sciences Center Samuel Shubrooks Beth Israel Deaconess None None None None None None None Medical Center John Strobel IMA, Inc None None None None None None None Stuart A. Winston Michigan Heart, PC Medtronic*; None Boston None None None None Boston Scientific* Scientific* This table represents the relationships of reviewers that may be perceived as actual or reasonably perceived conflicts of interest as reported on the Disclosure Questionnaire, which all reviewers are required to complete and submit. A relationship is considered to be “significant” if (1) the person receives $10 000 or more during any 12-month period, or 5% or more of the person’s gross income; or (2) the person owns 5% or more of the voting stock or share of the entity, or owns $10 000 or more of the fair market value of the entity. A relationship is considered to be “modest” if it is less than “significant” under the preceding definition. *Modest. †Significant.

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A new terminology for left KEY WORDS: AHA Scientific Statements Ⅲ electrocardiography Ⅲ infarction ventricular walls and location of myocardial infarcts that present Q wave Ⅲ ischemia Ⅲ electrophysiology AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part VI: Acute Ischemia/Infarction: A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: Endorsed by the International Society for Computerized Electrocardiology Downloaded from Galen S. Wagner, Peter Macfarlane, Hein Wellens, Mark Josephson, Anton Gorgels, David M. Mirvis, Olle Pahlm, Borys Surawicz, Paul Kligfield, Rory Childers and Leonard S. Gettes

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