Electrocardiographic assessment of repolarization heterogeneity

Abstract

Repolarization heterogeneity refers to differences in repolarization instants in the heart. Normally, repolarization in the human heart is a relatively smooth, continuous process, during which adjacent areas repolarize almost simultaneously. Several drugs or cardiac diseases may disturb the repolarization and thus increase the repolarization heterogeneity, which predisposes to arrhythmias. A non-invasive index able to assess this repolarization heterogeneity would have great clinical value. The standard 12-lead electrocardiogram (ECG) is attractive for this purpose as it is widely used and reflects repolarization heterogeneity. We used mathematical simulations to demonstrate that increased repolarization heterogeneity caused by increased APD heterogeneity in normally excited hearts is reflected in the T-wave amplitude, T-wave area, T-wave symmetry, and, with restrictions, in T-wave complexity and the Tapex-Tend interval. Our measurements in normal subjects suggest that hypertensive stress and recovery from exercise are conditions in normal hearts during which repolarization heterogeneity is increased. Immediately after vigorous exercise repolarization heterogeneity is largest. Pulmonary valve replacement in Fallot patients decreases QRS duration and electrocardiographic indices of repolarization heterogeneity. Left ventricular pacing in heart failure patients leads to similar effects on the repolarization heterogeneity as traditional right ventricular pacing. Transmural repolarization heterogeneity cannot be assessed from the electrocardiogram during pacing, as T wave morphology in paced hearts is predominated by the global repolarization pattern induced by pacing.