Prognostic Significance of T Wave Alternans

Sudden cardiac death accounts for approximately 400,000 deaths each year in the United States and remains a health problem of epidemic proportions. Most sudden cardiac deaths are caused by fatal ventricular arrhythmias. An effort aimed at the primary prevention of sudden cardiac death requires efficient identification of patients who are at high enough risk for having these arrhythmias to warrant aggressive prophylactic therapy. A number of recently completed, randomized clinical trials have demonstrated that an implantable cardiac defibrillator (ICD) can prevent sudden cardiac death in a highly selected group of high-risk patients. When these trials are viewed together, the only patients in whom the prophylactic implantation of an ICD has proven benefit are those patients identified by documented, spontaneous or inducible, sustained ventricular arrhythmias. Two randomized treatment trials (MADIT II, SCD-HEFT) tested the hypothesis that implantation of an ICD would reduce mortality in patients with congestive heart failure (CHF) and left ventricular dysfunction without any further risk tratification. However, the implications of these two trials-implantation of an ICD in every patient with CHF-were unlikely to be accepted either by the medical community or by health care payers. More efficient methods of risk stratification were necessary to identify those patients with CHF who were most likely to benefit from prophylactic treatment with an ICD. T Wave Alternans is a subtle every-other-beat variation in electrocardiographic T waves that is prognostic of patients at high risk for life-threatening cardiac arrhythmias and sudden cardiac death. It has recently been shown that T Wave Alternans (TWA) measured during exercise is strongly associated with inducible monomorphic CVT and with subsequent spontaneous arrhythmic events. This preliminary data suggest that TWA may be an efficient and non-invasive surrogate for electrophysiologic testing to screen patients who may be at high-risk for sudden cardiac death.