Rate-Dependent Repolarization Dynamics: Correlation between Electrocardiographic T Wave and U Wave

Abstract

U wave is the last ventricular repolarization component in electrocardiogram (ECG). Rate-dependent amplitude adaptation of U wave was less known relative to that of T wave. We experienced a patient presenting palpitation and showing ECG associated with clear physiologic upward U wave. Echocardiogram demonstrated no structural heart diseases and normal left ventricular (LV) function. T and U wave amplitudes were simultaneously plotted as a function of the preceding RR intervals using ambulatory ECG. U wave amplitude was augmented monotonously according to an increase of the preceding RR interval, whereas T wave amplitude was increased to the maximum level in the RR interval ranging from 1,000 to 1,500 msec and decreased to a steady-state level as RR interval was further prolonged. These indicate that rate-dependent repolarization gradient in T wave differs from that in physiologic U wave, which is mediated by mechano-electrical coupling under pause-dependent LV pressure and/or volume augmentation.