clinical Ambulatory
Alex McLellan Uwais Mohamed electrocardiographic monitoring
This article forms part of our ‘Tests and results’ series for 2011 which aims to provide information fitted at specialist cardiac laboratories and can about common tests that general practitioners order regularly. It considers areas such as indications, also be ordered by GPs. Implantable loop recorders what to tell the patient, what the test can and cannot tell you, and interpretation of results. are not currently rebateable on the Medicare Benefits Schedule (MBS), and are usually ordered Keywords: arrythmias, cardiac; diagnosis, differential; electrocardiography, ambulatory by cardiologists. When is it contraindicated? What is ambulatory Ambulatory electrocardiographic monitoring electrocardiographic monitoring? is contraindicated if it will delay appropriate hospitalisation or a more appropriate procedure. Ambulatory electrocardiographic monitoring (AECG) For example, AECG should not be part of the involves electrically monitoring a person’s cardiac initial investigation of intermittent stable angina; rhythm over a period of time while they go about their a stress test would be more appropriate. It is also day-to-day activities. The different types of AECG are: contraindicated in patients who have syncope Holter monitors, event recorders, and implantable loop and high risk features; inpatient admission is recorders (ILRs). appropriate (Table 1). The diagnostic yield from each test is variably low (Table 1); the pretest What are the indications? probability should define the method of AECG. • Palpitations of unclear cause despite clinical history Where does it fit in a diagnostic and electrocardiogram (ECG) approach? • Syncope or presyncope where an arrhythmia (bradycardia or tachycardia) is suspected as the Clinical history and examination is paramount in the underlying cause. workup of a patient with palpitations or syncope as Rarely AECG is indicated when pacemaker malfunction it will direct the correct investigation. For example, is suspected, in postmyocardial infarction, and for syncope (which is transient loss of consciousness follow up of arrhythmia on drug therapy.1 due to cerebral hypoperfusion) has many causes The frequency and suspected arrhythmia should (Table 2), and only 6–37% of syncope is attributed dictate the choice of investigation (Figure 1, Table 1). to cardiac causes.3 For patients with frequent symptoms (daily palpitations) A baseline 12-lead ECG should be performed a 24 hour continuous recording (Holter monitor) is before AECG. Basic blood tests: full blood appropriate – this is rarely indicated for syncope unless examination (FBE), urea, electrolytes and creatinine the frequency of events is less than weekly, although (UEC), calcium, magnesium and phosphate in this case, hospitalisation should be considered.2 (CMP), and thyroid function test (TFT) should be For patients with less frequent symptoms, an event considered, and in practice are often ordered recorder or ILR is more cost effective. before AECG. Holtor monitoring can be ordered by general Echocardiography or stress test/angiography practitioners, without specialist review, and performed should generally be performed before AECG if there at most pathology laboratories. Event recorders are is suggestion of structural or coronary heart disease.
596 Reprinted from Australian Family Physician Vol. 40, No. 8, AUGUST 2011 Ambulatory electrocardiographic monitoring clinical
What should I tell my patient? and is taken off for showering. The cutaneous symptoms with the ECG. The entire recording is electrodes can cause skin rash/irritation. The ILR analysed by a cardiac technician and physician The patient attends the laboratory to have the is roughly the size of a USB stick (Figure 3) and is skilled in the interpretation of AECGs. monitor fitted. Usually a full 12-lead ECG will positioned subcutaneously in the precordial region Event recorders are activated either be performed before applying the device. To under local anaesthetic in a minor day surgical prospectively (the device is applied by the patient ensure a good quality trace, skin preparation procedure performed by a cardiologist. when palpitations occur), or more commonly, may be required (eg. shaving). Five ECG leads Out-of-pocket costs to the patient vary: retrospectively. The retrospective event recorder are positioned on the chest for a Holter monitor there is a MBS rebate for Holter and event (also called external loop recorder) is worn and two leads for an event recorder (Figure monitors; currently there is no MBS rebate for continuously and records over 5–15 minute cycles, 2). The monitor/recorder (about the size of a ILRs; however, public hospitals or private health which are stored for analysis only if the patient mobile telephone) is carried on a belt or neck insurance will usually absorb the cost of an ILR. activates the device. The device also automatically strap. Holter monitor leads stay attached for stores rhythms beyond programmable upper and 24 hours, hence patients cannot shower during Hoes does it work? lower rate limits. The information can be remotely the test. Patients wearing an event recorder Holter monitoring continually records an ECG monitored by transtelephonic transmission. need to be educated in the reapplication of the tracing on three channels for 12–48 hours. The Event recorders cannot be activated by syncopal electrodes, as the recorder is worn for 1–4 weeks patient activates a button to correlate timing of patients; hence real time continuous telemetry device is indicated (essentially an event recorder that continuously records). Implantable loop recorders operate on the same Symptom principle as retrospective loop recorders and have a battery life of around 36 months. These devices can both be automatically activated or patient triggered.
Palpitations Syncope What do the results mean? Ambulatory electrocardiographic monitoring Symptoms Symptoms Symptoms Symptoms reports provide considerable information. Some key daily-weekly >weekly
Table 1. Types of ambulatory electrocardiographic monitoring3,4 Type of Indication Duration of test Yield Comment monitoring (frequency of (syncope; symptoms) arrhythmia) In hospital High risk features* 5 days (average syncope 16% High cost, reserved for high risk monitoring admission) Holter monitor Daily (mainly for 12–48 hours (can be Syncope <20% Low cost but expensive per palpitations) extended to ~2 weeks) Arrhythmia ~35% diagnosis Event recorder Weekly to monthly Week to month Syncope ~60% Patient compliance required Arrhythmia ~80% Implantable loop More than monthly 36 months (battery Syncope ~80% Minor surgical procedure, high recorder longevity) Arrhythmia 73%# initial cost; overall cost effective * Structural, congenital or coronary heart disease. Clinical or ECG features suggesting cardiac/arrhythmic syncope (eg. syncope during exertion or supine, absence of external factors or family history of sudden cardiac death # The yield for implantable loop recorders where palpitations are infrequent (less than one event per month) and where external loop recorder yield is ~20%
Reprinted from Australian Family Physician Vol. 40, No. 6, juLy 2011 597 clinical Ambulatory electrocardiographic monitoring
• bradycardia: consider cardiology referral as a atrioventricular [AV] block) test, catheter ablation). If atrial fibrillation (AF) is pacemaker may be indicated in patients with • tachycardia: consider cardiology review for detected, anticoagulation should be considered in symptomatic bradyarrhythmia (eg. daytime institution of appropriate anti-arrhythmic correlation with cardio-embolic risk heart rate <40 bpm; pauses >3 seconds; second therapy ± further diagnostic/management tests • runs of nonsustained or sustained ventricular degree [Mobitz II], advanced or third degree (eg. transthoracic echocardiography, stress tachycardia warrant cardiology review • Heart rate variability may be reported and can 3 Table 2. Classification of syncope indicate chronotropic intolerance/sinus node Reflex Orthostatic Cardiac dysfunction. Vasovagal Volume depletion Bradycardia: What don’t the results tell you? • sinus node dysfunction (including tachybrady syndrome) Arrhythmia does not always occur during the monitored • atrioventricular conduction defects period (Table 1). Ambulatory electrocardiographic • device malfunction monitoring is not designed to detect cardiac ischaemia Situational (eg. Drug induced (eg. Tachycardia: supraventricular or and it does not record ambulatory blood pressure. micturition alcohol, vasodilators) ventricular syncope) What are the next steps if the test is Carotid sinus 1° autonomic failure (eg. Drug induced bradycardia or negative or inconclusive? syncope multiple system atrophy) tachycardia If Holter monitor is negative, consider an event Atypical (without 2° autonomic failure (eg. Structural heart disease (eg. aortic apparent cause) diabetes) stenosis, hypertrophic obstructive record as this has a higher diagnostic yield. If cardiomyopathy AECG is negative with high risk clinical or ECG features, consider cardiology referral. For example, bradyarrhythmia may be the suspected cause of syncope in those with trifascicular block; or SVT may be the likely diagnosis in those with rapid onset and offset of brief palpitations. Artificial ‘noise’ (eg. from lead movement during walking) makes computer – and physician – analysis inaccurate, potentially causing false positives and false negatives. Attention to appropriate skin preparation, Figure 2. Patient wearing a Holter monitor ECG lead placement and patient education can minimise Note: ‘Event’ button (centre of monitor) that Figure 3. Implantable loop recorder: Medtronic noise in AECG tracings. the patient depresses if symptoms develop Reveal® device Authors Alex McLellan MBBS, BAppSc, is Cardiology Fellow, Department of Cardiology, St Vincent’s Hospital, Melbourne, Victoria. [email protected] Uwais Mohamed MBBS, FRACP, FCSANZ, is a cardiolo- The report body gist, Department of Cardiology, St Vincent’s Hospital, will include a Melbourne, Victoria. comment on ectopy. Infrequent Conflict of interest: none declared. The report body ectopics and one comments on couplet in this References the dominant 1. Cardiac Society of Australia and New Zealand. Guidelines case are of limited rhythm, rate and for ambulatory electrocardiographic monitoring, August significance. pauses. In this case 2009. Available at www.CSANZ.org.au/guidelines. 2. Kadish A, Buxton AE, Kennedy HL, et al. ACC/AHA Clinical episodes of AF with competence statement on electrocardiography and ambu- Conclusion rapid ventricular latory electrocardiography. Circulation 2001;104;3169–78. summarises response correlate 3. The European Society of Cardiology, Moya A, Sutton R, important findings. with symptoms; Ammirati F, et al. Guidelines for the diagnosis and man- In this case, the increasing rate agement of syncope. Eur Heart J 2009;30:2631–71. nocturnal pause is control mediation 4. Zimetbaum P, Goldman A. Ambulatory arrhythmia monitoring: choosing the right device. Circulation not significant. would be indicated. 2010;122;1629–36.
Figure 4. Example of AECG report with comments
598 Reprinted from Australian Family Physician Vol. 40, No. 8, AUGUST 2011