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A Comparison of T-Wave Alternans, Signal Averaged Electrocardiography and Programmed Ventricular Stimulation for Arrhythmia Risk Stratification Michael R

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A Comparison of T-Wave Alternans, Signal Averaged Electrocardiography and Programmed Ventricular Stimulation for Arrhythmia Risk Stratification Michael R View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Journal of the American College of Cardiology Vol. 36, No. 7, 2000 © 2000 by the American College of Cardiology ISSN 0735-1097/00/$20.00 Published by Elsevier Science Inc. PII S0735-1097(00)01017-2 A Comparison of T-Wave Alternans, Signal Averaged Electrocardiography and Programmed Ventricular Stimulation for Arrhythmia Risk Stratification Michael R. Gold, MD, PHD, FACC,* Daniel M. Bloomfield, MD, FACC,† Kelley P. Anderson, MD, FACC,‡ Nabil E. El-Sherif, MD, FACC,§ David J. Wilber, MD, FACC,࿣ William J. Groh, MD, FACC,†† N. A. Mark Estes, III, MD, FACC,# Elizabeth S. Kaufman, MD, FACC,†† Mark L. Greenberg, MD, FACC,** David S. Rosenbaum, MD, FACC** Baltimore, Maryland; New York, and Brooklyn, New York; Pittsburgh, Pennsylvania; Chicago, Illinois; Indianapolis, Indiana; Boston, Massachusetts; Cleveland, Ohio; Lebanon, New Hampshire OBJECTIVES The goal of this study was to compare T-wave alternans (TWA), signal-averaged electro- cardiography (SAECG) and programmed ventricular stimulation (EPS) for arrhythmia risk stratification in patients undergoing electrophysiology study. BACKGROUND Accurate identification of patients at increased risk for sustained ventricular arrhythmias is critical to prevent sudden cardiac death. T-wave alternans is a heart rate dependent measure of repolarization that correlates with arrhythmia vulnerability in animal and human studies. Signal-averaged electrocardiography and EPS are more established tests used for risk stratification. METHODS This was a prospective, multicenter trial of 313 patients in sinus rhythm who were undergoing electrophysiologic study. T-wave alternans, assessed with bicycle ergometry, and SAECG were measured before EPS. The primary end point was sudden cardiac death, sustained ventricular tachycardia, ventricular fibrillation or appropriate implantable defibrillator (ICD) therapy, and the secondary end point was any of these arrhythmias or all-cause mortality. RESULTS Kaplan-Meier survival analysis of the primary end point showed that TWA predicted events with a relative risk of 10.9, EPS had a relative risk of 7.1 and SAECG had a relative risk of 4.5. The relative risks for the secondary end point were 13.9, 4.7 and 3.3, respectively (p Ͻ 0.05). Multivariate analysis of 11 clinical parameters identified only TWA and EPS as independent predictors of events. In the prespecified subgroup with known or suspected ventricular arrhythmias, TWA predicted primary end points with a relative risk of 6.1 and secondary end points with a relative risk of 8.0. CONCLUSIONS T-wave alternans is a strong independent predictor of spontaneous ventricular arrhythmias or death. It performed as well as programmed stimulation and better than SAECG in risk stratifying patients for life-threatening arrhythmias. (J Am Coll Cardiol 2000;36:2247–53) © 2000 by the American College of Cardiology Accurate identification of patients at increased risk for (2–5). Recently, programmed ventricular stimulation during sustained ventricular arrhythmias is critical for the develop- electrophysiology (EPS) testing (6,7), but not signal aver- ment of effective strategies to prevent sudden cardiac death. aged electrocardiography (SAECG) (8), identified a cohort Traditionally, left ventricular ejection fraction and measures with left ventricular dysfunction who had improved survival of ambient arrhythmia were used to identify high-risk with implantable cardioverter-defibrillator (ICD) place- ment. However, programmed stimulation is invasive and See page 2254 costly. Accordingly, improved noninvasive markers of ar- rhythmia vulnerability are needed. In this regard, T-wave cohorts and to evaluate the utility of the prophylactic alternans (TWA) is a promising new technique (9). administration of antiarrhythmic drugs (1). Unfortunately, T-wave alternans is a heart rate-dependent measure of this strategy has not proven beneficial in reducing mortality repolarization (10). Previously, TWA induced with atrial pacing was shown to predict ventricular arrhythmias in patients undergoing EPS (11). Subsequently, techniques From the *Department of Medicine, Division of Cardiology, University of Maryland Medical System, Baltimore, Maryland; †Columbia Presbyterian Medical were developed to allow assessment of alternans noninva- Center, New York, New York; ‡University of Pittsburgh Medical Center, Pittsburgh, sively with exercise. There is a high concordance between Pennsylvania, §Veterans Affairs Medical Center, Brooklyn, New York; ࿣University of exercise-induced and pacing-induced TWA (12). More- Chicago Hospitals, Chicago, Illinois; ¶Indiana University, Indianapolis, Indiana; #New England Medical Center, Boston, Massachusetts; **MetroHealth Campus, over, TWA measured noninvasively predicts the induction Case Western Reserve University, Cleveland, Ohio, and ††Dartmouth Hitchcock of ventricular tachyarrhythmias at EPS (13) as well as Medical Center, Lebanon, New Hampshire. Supported by a grant from Cambridge appropriate discharges in patients with ICDs (14). How- Heart, Inc., Bedford, Massachusetts. Manuscript received February 22, 2000; revised manuscript received August 2, ever, the predictive value of TWA measured noninvasively 2000, accepted August 11, 2000. in patients undergoing arrhythmia evaluation is unknown. 2248 Gold et al. JACC Vol. 36, No. 7, 2000 Comparison of TWA, SAECG and EPS December 2000:2247–53 independent physician readers blinded to the patient’s Abbreviations and Acronyms clinical data. The concordance rate between readers was EPS ϭ programmed ventricular stimulation during 97% for determinate tests. electrophysiology study Signal averaged electrocardiography. Signal averaged ϭ ICD implantable cardioverter-defibrillator electrocardiography was performed in the supine resting SAECG ϭ signal averaged electrocardiogram TWA ϭ T-wave alternans position before EPS. Time domain analysis was performed VTE ϭ ventricular tachyarrhythmic event on signals from orthogonal leads using LP-Pac Q software (Arrhythmia Research Technology, Inc., Austin, Texas). The duration of signal collection was determined automat- Ͻ ␮ Accordingly, this study was a prospective evaluation of the ically to reduce mean noise levels to 0.5 V. The results were considered indeterminate if the unfiltered QRS dura- role of TWA in predicting spontaneous ventricular arrhyth- Ͼ mias in a large cohort undergoing EPS. In addition, a tion was 120 ms with or without bundle branch block or comparison of TWA with SAECG and programmed stim- if a low noise recording could not be achieved. For inter- ulation was performed. pretable studies, the SAECG was considered positive if two or three of the standard measurements of the filtered signal Ͼ METHODS were abnormal: the QRS duration 114 ms, the root mean square voltage of the terminal 40 ms of the QRS Ͻ20 ␮V Patient population. This was a prospective, multicenter or the duration of the terminal QRS less than 40 ␮V study of 337 patients undergoing diagnostic electrophysiol- Ͼ38 ms. ogy studies. Patients were considered for inclusion if they Programmed ventricular stimulation. The EPS was per- were in normal sinus rhythm and capable of bicycle exercise. formed in subjects in the supine, mildly sedated, postab- Beta-adrenergic blocking agents were withheld for at least sorptive state by standard techniques. Programmed ventric- 24 h before the study to reduce the risk of an inadequate ular stimulation was performed using a stimulus duration of heart rate response with exercise. Twenty-four patients were 2-ms at an amplitude of two to three times the diastolic excluded from analysis because of protocol violations (for threshold. The stimulation protocol consisted of up to two example, electrophysiology studies or TWA not performed, or three extrastimuli delivered from the right ventricular TWA testing performed after electrophysiologic testing, apex and outflow tract at two drive cycle lengths. The beta-blockers not withheld). Thus, data are presented on number of extrastimuli employed and detailed protocol used the cohort of 313 patients enrolled in this trial without a was individualized at each center. However, for patients protocol violation. Informed consent was obtained from with a history of ventricular tachyarrhythmias, three extra- each patient, and the study was approved by the institutional stimuli were required. The end point of EPS was the review boards of the participating institutions. induction of sustained monomorphic ventricular tachycardia TWA measurement. T-wave alternans testing was con- (Ͼ30 s in duration or associated with hemodynamic com- ducted before EPS. Careful skin preparation including mild promise requiring earlier intervention) or the completion of abrasion and high resolution electrodes (High-Res, Cam- the stimulation protocol. The induction of ventricular fi- bridge Heart, Inc., Bedford, Massachusetts) were used to brillation was defined prospectively as an indeterminate minimize noise. T-wave alternans was measured during result. submaximal bicycle exercise to achieve a heart rate of 105 to Assessment of spontaneous ventricular arrhythmias. 110 beats/min. Electrocardiographic leads were placed at Clinical follow-up was obtained at regular intervals. The the standard 12-lead positions and in an orthogonal X,Y,Z primary end point was the occurrence of a ventricular configuration. Measurements were made with the CH2000 tachyarrhythmic event (VTE), which was defined prospec- system (Cambridge
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