Repolarization Heterogeneity: Beyond the QT Interval

R esearch over the past 2 decades has suggested that significant differences exist in the action potentials of endocardial, epicardial, and mid-myocardial (M) cells that comprise the ventricular myocardium. Relative differences in the time course of repolarization of these 3 cell types, referred to as transmural dispersion of repolarization (TDR), is largely responsible for the inscription of the T wave on the electrocardiogram (ECG). Both the morphology and duration of the T wave appear to represent underlying heterogeneity in repolarization, a process initially linked to increased risk of arrhythmia and sudden death in patients with congenital long QT-syndrome (LQTS). It is increasingly apparent that repolarization heterogeneity is present in a variety of cardiovascular diseases and syndromes and is even predictive of sudden death in the general population. Furthermore, repolarization heterogeneity has also been associated with abnormalities in myocardial mechanics, a finding that may have direct implications for understanding the pathophysiology and treatment of heart failure. This review will focus on summarizing current understanding of repolarization heterogeneity, with particular focus on clinical implications.