Risk Stratification for Sudden Cardiac Death: The Need to Go Beyond the Left Ventricular Ejection Fraction

Sudden cardiac death (SCD) accounts for as many as 450,000 deaths yearly in the United States. Over the last 15 years, many clinical trials have established the effectiveness of an implantable cardioverter-defibrillator (ICD) in reducing sudden and total mortality in patients with structural heart disease. However, controversy remains about exactly how to identify the patients most likely to benefit from an ICD, as well as those who may safely do without an ICD implant. The first primary prevention ICD trials used an abnormal electrophysiological study in addition to a low left ventricular ejection fraction (LVEF) as high-risk markers for SCD. More recent ICD trials selected patients based on the presence of a low LVEF alone. Ideally, noninvasive electrophysiological markers that more directly reflect arrhythmia substrates may better identify patients for prophylactic ICD implant. Several of these markers have been associated with the risk of SCD, but all have yielded contradictory outcome results or have not been tested prospectively. This review focuses on the most promising tests to date, their clinical significance, and their possible use to improve efficacy and efficiency of risk stratification for SCD.