T wave (repolarization) alternans: Technical aspects
- Sanjiv M Narayan, MD, PhD
Sanjiv M Narayan, MD, PhD
- Professor of Medicine
- Stanford University School of Medicine
T-wave alternans (TWA) refers to periodic beat-to-beat variability in the timing, shape, and/or amplitude of T-waves on the surface electrocardiogram (ECG) [1,2]. TWA therefore reflects sudden changes in temporal heterogeneity in ventricular repolarization, which is an important mechanism underlying reentrant arrhythmias [3,4].
Despite the term "T-wave" alternans, alternating behavior may also involve the ST segment and U wave (figure 1) [2,5-8]. As a result, the term ventricular repolarization alternans may be more accurate, but is rarely used.
TWA of sufficient magnitude to be seen with visual inspection is uncommon. With the development of computerized filtering and spectral analysis tools, TWA on the order of microvolts can be detected, and microvolt TWA (MTWA, now often used synonymously with TWA) is both sensitive and specific for predicting ventricular arrhythmias in a number of clinical scenarios [1,2,7,9-16].
The technical aspects of TWA testing will be reviewed here. The clinical utility of TWA is discussed separately. (See "T wave (repolarization) alternans: Clinical aspects".)
THE PATHOPHYSIOLOGY OF TWA
Originally, microvolt and macrovolt-level TWA were considered to be distinct entities. However, studies from isolated guinea pig and rabbit hearts now suggest that these forms of TWA may differ only quantitatively and represent the same pathophysiological processes of dispersion of repolarization [4,17]. (See "Myocardial action potential and action of antiarrhythmic drugs".)
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