What Is the Clinical Significance of Ventricular Repolarization Abnormalities during Supraventricular Tachyarrhythmias?

Abstract

T wave changes can be classified as either primary or secondary. Primary T wave changes have been defined as the result of uniform or nonuniform changes in action potential duration in the absence of changes in the sequence of activation. Secondary T wave changes have been defined as reflecting changes in the sequence of repolarization that result solely from changes in the sequence of activation, without any abormalities in the duration and shape of action potentials [1–3]. However, Chatterjee et al. [4] and Rosenbaum et al. [5] demonstrated that prolonged alteration in the sequence of activation caused by ventricular pacing not only caused secondary T wave changes during the period of pacing, but that conspicuous T wave changes persisted for a long time after pacing was terminated and a normal supraventricular activation pattern had resumed. In other affections, such as intermittent left bundle branch block, ventricular tachycardia, or ventricular preexitation transient T wave alterations can be present. These alterations persist after normalization of ventricular activation and, for the most part, in the absence of known myocardial disease that would allow these T wave changes to be classified as primary. This finding has been interpreted as “memory”, that is the heart adjusts its repolarization to an altered activation sequence and retains the adapted state long after the activation sequence in normalized. However, the basic electrophysiological mechanism of “cardiac memory” is controversial.