Sex differences in the rate dependence of the T wave descending limb

OBJECTIVE: The interval from the peak to the end of the T wave (TpTe) has been proposed to reflect the heterogeneity of action potential durations within the ventricular wall. Several studies have previously described TpTe to be independent of heart rate, which contradicts the in vitro observation of marked changes in transmural repolarisation heterogeneity due to cycle length changes. Because of this inconsistency, we investigated heart rate related changes of TpTe interval. METHODS: During 24-h recordings (SEER MC, Marquette GE) in healthy young women (n=25, 26+/-7 years) and men (n=25, 27+/-8 years), a 10-s 12-lead ECG was obtained every 30 s. Recordings were repeated after 1 day, 1 week, and 1 month and results in each subject were pooled together and grouped for women and men. The QT and QT(peak) intervals were obtained automatically using QT Guard software (Marquette) and TpTe was computed as the difference between QT and QT(peak). In each subject TpTe values were averaged over 10-ms RR interval bands from 550 to 1150 ms. RESULTS: In both sexes, TpTe interval showed marked rate dependence with prolongation at long RR intervals. TpTe intervals in men were significantly longer over the entire range of investigated RR intervals (P=1.4x10(-25)). However, whereas the difference between sexes was marked at short cycle length (RR interval bin 540-550 ms: women 87+/-5 vs. men 95+/-9, P=5.1x10(-4)) it decreased at long cycle lengths (RR interval bin 1140-1150 ms: women 99+/-5 vs. men 106+/-6, P=9.3x10(-4)). CONCLUSION: There is a marked rate dependence of TpTe interval, which differs between women and men. The finding is consistent with the TpTe interval being an approximate surrogate of the intraventricular repolarisation gradient. The rate dependent increase in transmural repolarisation heterogeneity might be one of the reasons for the increased propensity of torsades de pointes in women.