T wave alternans: a marker of myocardial instability

T wave alternans is an electrocardiographic marker of myocardial electrical instability considered predictive for the development of lethal ventricular rhythms. Direct observation of this phenomenon on the electrocardiogram is rare. Subtle, nonvisible alternation of the T wave may be detected at the microvolt level using advanced signal processing techniques. This technology has enabled investigators and clinicians to identify and risk-stratify certain groups at high risk for sudden cardiac death. The purpose of this review is to discuss the concept of T wave alternans in relation to all cardiac alternans, provide an overview of its proposed mechanisms, and address the clinical utility of this electrocardiographic marker of myocardial electrical instability.