Repolarization alternans: techniques, mechanisms, and cardiac vulnerability.

Sudden cardiac death continues to be the leading cause of mortality in developed countries. Electrical alternans of the ST segment and the T wave on the surface ECG as a noninvasive marker of patients at risk is a phenomenon that was initially observed early in this century and was seen then to be associated with cardiac rhythm disturbances. Substantial evidence indicates that T wave alternans (TWA) is related to myocardial ischemic as a harbinger of malignant ventricular arrhythmias because it reflects dispersion and heterogeneity of repolarization. Recent data have demonstrated a significant correlation between TWA and vulnerability to ventricular arrhythmias in individuals with or without organic heart disease, it also predicts the results of electrophysiological testing and arrhythmia-free survival in patients with a variety of cardiac diseases. This article reviews the historical background of TWA and discusses the early experimental and recent clinical evidence implying an integral link between TWA and ischemia-induced cardiac vulnerability.