Sexual dimorphism in the electrocardiographic dynamics of human ventricular repolarization - Characterization in true time domain

Background-Previous characterizations of sex differences in ST-T waveform voltages have largely focused on amplitudes at selected time points during repolarization, subject to potential distortions from variations in heart rate (HR) or reliance on a JT-normalized time scale. Methods and Results-Using digitized 12-lead ECGs from 553 normal adults (426 males) with HRs confined to 60 +/- 1, 70 +/- 1, or 80 +/- 1 bpm, we derived X, Y, and Z lead voltages and then generated, for each HR category by sex, summary (population mean) resultant spatial vector amplitudes (ST-T-XYZ) and instantaneous slopes (dV/dt(XYZ)) at successive 4-ms intervals following the J point. Within each HR category, then was an early intersex divergence of ST-T-XYZ trajectories (95% CIs nonoverlapping), with men exhibiting 2- to 3-fold greater dV/dt(XYZ) values during the ST segment and achieving greater maximum T-XYZ and dV/dt(XYZ) values than women; descending T-XYZ limbs were relatively more concordant between sexes but still steeper in men. The early sex differences in repolarization dynamics persisted in multiple regression analyses that took into account age and a morphometric index of left ventricular mass. In men, absolute values of extrema of T-XYZ and dV/dt(XYZ) varied inversely with HR. Conclusions-At physiological resting HRs, the spatial ST-T vector voltage time trajectory is steeper in men than in women, beginning virtually from the J point. In addition to its mechanistic implications, the demonstration of marked sensitivity of ST-T-XYZ and especially dV/dt(XYZ) to sex raises the possibility that these time-based, EGG-derived parameters might be informative in pathophysiological studies of ventricular repolarization.