Electrocardiographic estimates of action potential durations and transmural repolarization time gradients in healthy subjects and in acute coronary syndrome patients—profound differences by sex and by presence vs absence of diagnostic ST elevation

Abstract

Action potential duration (APD) changes increasing repolarization time (RT) dispersion are potentially arrhythmogenic. A repolarization model developed from electrocardiographic data of 5376 healthy men and women was used to derive parameter estimates for APD and RT and their transmural gradients (RT grad and APD grad, respectively) in myocardial infarction patients, 126 with and 658 without diagnostic ST elevation (STEMI and NSTEMI, respectively). The model uses, as covariates, rate-adjusted QT and QT peak intervals (QT a and QT pa, respectively) and diagonal crossmural RT grad derived as T p-T xd, the interval from T p to the inflection point at descending limb of global T wave. An additional parameter is Θ(T|T ref), the spatial angle between a subject's T vector and the average T vector of the normal reference group. If Θ(T|T ref) >0, QT pa is assigned to RT epi and QT pa + RT grad to RT endo, with RT epi and RT endo assignments reversed if Θ(T|T ref) ≤0. Parameter estimates for APD epi and APD endo were shorter in men than in women (by 17 ms and 14 ms, respectively, P < .001 for both). Compared to the reference group, RT epi in the STEMI group was shortened by 14 ms in men and by 18 ms in women ( P < .001 for both) with a lesser decrease in RT endo suggesting predominantly subepicardial ischemia. In NSTEMI only RT endo was shortened, by 6 ms in males ( P < .01) and 10 ms in females ( P < .001), suggesting subendocardial ischemia. RT grad signifying local crossmural RT dispersion was prolonged in STEMI by 8 ms in men and by 11 ms in men ( P < .001 for both). RT grad was not changed significantly in NSTEMI. Rate-adjusted T p-T e interval signifying global RT dispersion was increased in both MI and in both sex groups ( P <.001 for all). In conclusion, QT prolongation observed in NSTEMI without prolongation of RT grad and APD epi suggests a delay during terminal repolarization, and in contrast, in STEMI, QT is not changed significantly in spite of prolonged RT grad because of shortened APD epi and RT epi. These repolarization abnormalities are not revealed by QT alone but readily by the repolarization model.