[Technical and practical aspects of T-wave alternans testing]

Alternation of the amplitude of the repolarization wave (T-wave) of the body surface ECG, usually referred to as T-wave alternans (TWA), has become one of the most important noninvasive tools in cardiac risk stratification. In earlier experimental and clinical studies TWA was shown to predict an individual's susceptibility of ventricular tachyarrhythmias. Recently, a number of prospectively designed clinical studies have confirmed these results and demonstrated that a positive TWA result in high risk populations, such as post-myocardial infarction patients and individuals suffering from congestive heart failure, is a very useful prognostic marker heralding sudden cardiac death due to ventricuar tachyarrhythmias. Moreover, experiments, performed in animals as well as in computer models, have shown that T-wave alternans may also be mechanistically involved in arrhythmogenesis. Since it has now become possible to measure TWA completely noninvasively by menas of exercise testing, an exponential increase in TWA tests has been observed. However, little information on the technical aspects of TWA testing is available. Therefore, in this article, technical and practical aspects of TWA assessment and interpretation are reviewed as far as they are relevant for clinicians.