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T wave (repolarization) alternans: Technical aspects

Sanjiv M Narayan, MD, PhD
Section Editor
Ary L Goldberger, MD
Deputy Editor
Brian C Downey, MD, FACC


T-wave alternans (TWA) refers to beat-to-beat variability in the timing or shape of T-waves on the surface electrocardiogram (ECG) [1,2]. TWA therefore reflects 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 repolarization alternans may be more accurate, but is rarely used.

TWA does not involve the QRS complex and is distinct from electrical alternans totalis. This term refers to an alternating axis and/or voltage of all ECG components and is typically seen with the cardiac motion associated with large pericardial effusions [9]. (See "Diagnosis and treatment of pericardial effusion", section on 'ECG findings'.)

TWA was first linked to ventricular arrhythmias in the early 1900s in cases that were evident on visual inspection of the ECG [10,11]. Visually apparent TWA was subsequently reported in a variety of settings including ischemia and long QT syndrome (LQTS) [12,13]. (See "Clinical features of congenital long QT syndrome".)

TWA of sufficient magnitude to be seen with visual inspection is uncommon. With the recent 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 [1,2,7,14-21]. TWA has been approved by the United States Food and Drug Administration (FDA) for noninvasively predicting the risk for life-threatening ventricular arrhythmias.


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Literature review current through: Feb 2017. | This topic last updated: Oct 21, 2015.
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