Age, gender, and autonomic tone effects on surface electrocardiographic indices of ventricular repolarization

Prolonged QT offset dispersion (QToD), an index of heterogeneity of ventricular repolarization, is thought to be an independent predictor of all-cause and cardiovascular mortality. However the influence of gender and autonomic tone in healthy adults on age-related changes in measures of ventricular repolarization are not well characterized.

QToD and T wave complexity were measured in 56 healthy subjects with no detectable heart disease (by echo and stress test)-38 young subjects with a mean age of 28 +/- 4 years and 18 old subjects with a mean age of 71 +/- 7 years. QToD and T wave complexity were computed from 12-lead ECGs using the GE Marquette QT Guard automated analysis program with manual overreading at rest (baseline), following exercise, and double autonomic blockade with atropine and propranolol. Data was analyzed using factorial ANOVA.

Young males had a significantly greater QToD than young and old females at baseline (28 +/- 5 ms, 23 +/- 5 ms, and 22 +/- 5 ms, respectively, P < 0.01), an intrinsic effect independent of changes in autonomic tone. In contrast, females had significantly greater T wave complexity than males following exercise and double autonomic blockade with a definite trend at baseline. There was no correlation between T wave complexity and QToD.

Age and gender demonstrate a complex interaction on indices of myocardial repolarization with different measures behaving differently. These findings have implications for better understanding age and gender effects on myocardial electrophysiology.