T-wave alternans and the confounding role of the T-wave amplitude

The interpretation of the electrocardiogram (ECG) T-wave alternans (TWA) as positive or negative depends on its magnitude, regardless whether the frequency domain or the time domain analysis is employed. The author argues that a number of cardiac and extracardiac influences can confound the magnitude of TWA. The amplitude of the ECG T waves, considered in the measurement/calculation of TWA, and possibly myocardial edema are examples of cardiac influences. Peripheral edema with its effect in attenuating the amplitude of all components of the ECG, including the T waves, is an example of extracardiac influence. Another concern is the variation in the evolution of the T-wave amplitudes during the 3- to 6-month period after an acute myocardial infarction, and whether such variation confounds the results of the TWA testing, which often is undertaken at that time bracket. The T-wave amplitude changes may impact the sensitivity and specificity of TWA testing after an acute myocardial infarction. Perhaps the measured TWA magnitude should be adjusted to the amplitude of the T waves or voltage-time integral of the J-T interval, depending on the method used for the calculation of TWA. These issues need to be considered and investigated in an effort to render TWA testing more reliable in predicting sudden cardiac death.