Routine Ambulatory ECG for Hypertrophic Cardiomyopathy
Abstract & Commentary
With Comment by Michael H. Crawford, MD, Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco, Editor, Clinical Cardiology Alert.
Synopsis: In a community-based HCM cohort, ventricular and supraventricular tachyarrhythmias on AECG were frequent, but sudden death was uncommon.
Source: Adabag AD, et al. J Am Coll Cardiol. 2005;45: 697-704.
Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden death in adolescents; presumably due to ventricular arrhythmias. Tertiary care center studies have shown that nonsustained ventricular tachycardia (NSVT) predicts future events. Thus, ambulatory ECG monitoring (AECG) has been recommended as a routine risk stratification test in HCM patients. However, tertiary center patients may be biased toward sicker patients. Accordingly, this group studied a community based cohort of 535 HCM patients in the Minneapolis/St. Paul area of Minnesota (total population 8 million). Patients specifically referred to Dr. Barry Maron were excluded, leaving 296 patients mainly seen because of cardiovascular symptoms. Of these, 178 had at least 1 AECG. Most of those who did not have an AECG were < 20 or > 50 years old, an age where AECG has not been routinely recommended. AECG arrhythmias were then related to clinical outcome.
Results: Most (88%) had premature ventricular contractions (12% > 500, 42% couplets 31% NSVT) and 37% had supraventricular tachyarrhythmias (SVT). NSVT was associated with greater left ventricular hypertrophy and more severe symptoms.
SVT occurred more commonly in those with outflow obstruction. During a mean follow-up of 5.5 years, 6% died suddenly (annual mortality rate 1%); half of whom had NSVT on AECG (negative predictive value 95%). Adabag and colleagues concluded that in a community-based HCM cohort, ventricular and supraventricular tachyarrhythmias on AECG were frequent, but sudden death was uncommon. Ventricular tachyarrhythmias had a high negative predictive value for sudden death in this population.
Comment
The major strength of this study is that efforts were made to minimize the tertiary referral center bias. Unfortunately, this lead to a low sudden death event rate, decreasing the power to detect predictors of mortality. Although there was a trend toward more sudden death in those with NSVT, it was not statistically significant. All Adabag et al could conclude was that a negative AECG study was reassuring to the patients. Unfortunately, few had a benign AECG; 90% had PVCs with an average of > 300/24-hours, and most had major complex ventricular arrhythmias.
Interestingly, few were symptomatic; only 3% with NSVT reported palpitation, and none had syncope. Not surprisingly, ventricular arrhythmias correlated with more severe disease both subjectively and objectively.
Other limitations of this study include the following. Only echocardiography was used for diagnosis, so we do not have data on high-risk genetic profiles and their propensity to arrhythmias. Drug therapy was not controlled. Most of the patients were on beta- or calcium-blockers and a few amiodarone, but 12% had a prophylactic defibrillator before the AECG. Children and older adults were underrepresented.
Although this study is not particularly compelling because of the high incidence of serious arrhythmias and the low event rate, a benign AECG would be of some value to the patient’s psyche. Therefore, until we know more about genetic analysis and other predictors, AECG should remain a standard test in the evaluation of HCM patients.
In a community-based HCM cohort, ventricular and supraventricular tachyarrhythmias on AECG were frequent, but sudden death was uncommon.
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