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

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 (RTgrad and APDgrad, 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 (QTa and QTpa, respectively) and diagonal crossmural RTgrad derived as Tp-Txd, the interval from Tp to the inflection point at descending limb of global T wave. An additional parameter is Θ(T|Tref), the spatial angle between a subject's T vector and the average T vector of the normal reference group. If Θ(T|Tref) >0, QTpa is assigned to RTepi and QTpa + RTgrad to RTendo, with RTepi and RTendo assignments reversed if Θ(T|Tref) ≤0. Parameter estimates for APDepi and APDendo were shorter in men than in women (by 17 ms and 14 ms, respectively, P < .001 for both). Compared to the reference group, RTepi 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 RTendo suggesting predominantly subepicardial ischemia. In NSTEMI only RTendo was shortened, by 6 ms in males (P < .01) and 10 ms in females (P < .001), suggesting subendocardial ischemia. RTgrad signifying local crossmural RT dispersion was prolonged in STEMI by 8 ms in men and by 11 ms in men (P < .001 for both). RTgrad was not changed significantly in NSTEMI. Rate-adjusted Tp-Te 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 RTgrad and APDepi suggests a delay during terminal repolarization, and in contrast, in STEMI, QT is not changed significantly in spite of prolonged RTgrad because of shortened APDepi and RTepi. These repolarization abnormalities are not revealed by QT alone but readily by the repolarization model.