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(Circulation. 2001;104:32.)
© 2001 American Heart Association, Inc.

Clinical Investigation and Reports

Sexual Dimorphism in the Electrocardiographic Dynamics of Human Ventricular Repolarization

Characterization in True Time Domain

Michael H. Lehmann, MD; Hua Yang, PhD

From the Department of Internal Medicine (M.H.L.), Division of Cardiology, University of Michigan and Veterans Administration Medical Center, Ann Arbor, Mich, and Sinai Hospital (M.H.L., H.Y.), Detroit, Mich.

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, there 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, ECG-derived parameters might be informative in pathophysiological studies of ventricular repolarization.

Key Words: electrocardiography • sex • heart rate

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