Risk stratification for arrhythmic events: are the bangs worth the bucks?

More than 800,000 North Americans are admitted to the hospital each year with an acute myocardial infarction (MI) (1,2). Most of these patients survive until hospital discharge, but a substantial number of the survivors will die of out-of-hospital arrhythmic events (3). Approximately half the deaths that occur following acute MI are attributable to recurrent ischemic events or to congestive heart failure related to left ventricular impairment (3,4). A plethora of clinical trials and guideline statements have addressed the issue of post-MI risk stratification with respect to these complications. However, lethal arrhythmias cause approximately half the deaths that occur during the first year after acute MI (5,6). Unfortunately, little information is available to guide us in the appropriate stratification of patients at risk for this complication. Various tests have been proposed as being useful for post-MI stratification of patients at risk of major arrhythmic events. Investigators have found that measures of left ventricular function are particularly useful (7). Other tests that have been closely examined include signal-averaged electrocardiogram (SAECG) (8) and Holter monitoring. Several aspects of Holter monitoring have been correlated with the risk of arrhythmic events, including the incidence of premature ventricular contractions, the occurrence of major arrhythmias and a reduction in heart rate variability (HRV) (9). Electrophysiologic studies are thought to be especially predictive (10). More recently, various other techniques have been examined as possible predictors, including baroreflex sensitivity (11), QT dispersion (12), T-wave alternans (13), time-domain analysis (14), spectral turbulence analysis (14) and fractal dimension (15). Because no single diagnostic test has been found to have adequate predictive ability, investigators have examined the ability of various combinations of tests to predict arrhythmic events in the post-MI population. Based on the results of these studies, a number of testing algorithms have been proposed that combine the use of left ventricular ejection fraction (LVEF), SAECG, HRV and electrophysiologic studies (16 –21). Because of the cost and invasive nature of electrophysiologic studies, this test is usually reserved for the end of the algorithm when it can be used in small numbers of high-risk patients. Unfortunately, previous studies that examined combinations of tests were done in relatively small numbers of patients at a limited number of clinical centers. These studies had the advantage of performing several types of tests in the same patient population, but the studies were limited because of their size and generalizability. In this context, the report by Bailey …