Role of risk stratification after myocardial infarction.
Despite advances in medical and surgical therapy for patients with heart disease, sudden cardiac death remains an important public health problem that prematurely ends the lives of more than 300,000 persons each year in North America. Many of these deaths occur in patients with a history of myocardial infarction (MI). Although severe left ventricular (LV) systolic dysfunction is used to identify patients at risk of sudden death after MI, most cardiac arrests occur in those with only mild LV dysfunction. Further, severe LV dysfunction is not a specific indicator for cardiac arrest. Risk stratification, to identify patients most likely to benefit from implantable defibrillator therapy after MI, is an essential area of investigation. Because the development of cardiac arrest is complex and likely requires the confluence of several factors, using a single test to predict the risk of sudden death or to guide implantable defibrillator therapy is unlikely to be successful. Tests that assess cardiac structure, including repolarization, and those that evaluate autonomic modulation and other factors have been developed with the goal of identifying patients at highest risk of cardiac arrest after MI. These tests, particularly in combination, appear to identify patients who may benefit from implantable defibrillator therapy after MI. Ongoing and planned randomized controlled trials will assess whether these tests can be used to guide implantable defibrillator therapy. Until the data from these studies are available, severe LV dysfunction remains the only proven approach to guide implantable defibrillator therapy after MI.
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Derek V. Exner, MD, MPH Libin Cardiovascular Institute of Alberta, University of Calgary, 3330 Hospital Drive NW, Room G208, Calgary, AB, Canada T2N 4N1. exner@ucalgary.ca.
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