Beat-To-Beat Ventricular Repolarization Duration Variability Assessed By Cardiac Acceleration and Deceleration Phases in Athletes

Dynamic ventricular repolarization duration (VRD) and RR-interval coupling relates to autonomic control and myocardial electrical stability. Phase-rectification of RR-interval series separates acceleration (AC) and deceleration (DC) phases, reflecting sympathetic and parasympathetic influences on heart rate, respectively. To assess the effect of physical conditioning status on dynamic VRD and phase-rectification-driven RR-interval coupling. Controls (n = 10) and Athletes (n = 10) groups underwent 15 min resting ECG. RRinterval histogram was calculated, with 100 ms width classes, ranging from 700 ms to 1300 ms. RR-intervals and respective VRD, defined as the segment between R-wave peak and the apex of the T-wave (RTA) were grouped. The averages of RTA (MRTA) and RRintervals (MRR) were calculated, using the whole series, AC and DC phases, as well as root-mean-squared difference of consecutive RTA (RMS-RTA). Values were pooled, and compared inter groups and inter classes. Regression lines were calculated, and slope compared between groups (α<0.05). MRTA was larger in Athletes than in Controls. MRTA increased proportionally to MRR in both AC and DC, and slope was steeper in Athletes. MRTA slopes in AC and DC phases did show differences, in both groups. RMS-RTAC and RMSRTDC showed no intergroup differences. An inverse correlation between RMS-RTA and MRR was found only in Athletes, similarly in both phases. In athletes, VRD is larger, for all RR-interval durations, and RTA slope steeper than in heathy sedentary, indicating faster adaptation. In athletes, VRD variability decreases as RR-interval increases, indicating a beneficial effect of fitness on repolarization stability.