Time- and frequency-domain analysis of repolarization phase during recovery from exercise in healthy subjects

Background/aim: Recently, data from temporal dispersion of myocardial repolarization analysis have gained a capital role in the sudden cardiac death risk stratification. Aim of this study was to evaluate the influence of heart rate, autonomic nervous system and controlled breathing on different myocardial repolarization markers in healthy subjects. Method: Myocardial repolarization dispersion markers from short period (5-minutes) ECG analysis (time and frequency domain) have been obtained in 21 healthy volunteers during these conditions: free breathing (rest); controlled breathing (resp); the first 5-minutes of post-exercise recovery phases (exercisePeak); maximum sympathetic activation, and during the second five minutes of post-exercise recovery phases (exerciseRecovery), intermediate sympathetic activation. Finally, we analyzed the whole repolarization (QTe), the QT peak (QTp) and T peak - T end intervals (Te). Results: During the exercisePeak major part of repolarization variables changed in comparison to the rest and resp conditions. Particularly, QTe, QTp, Te standard deviations (QTeSD, QTpSD, TeSD), variability indexes (QTeVI, QTpVI), normalized variances (QTeVN, QTpVN, TeVN), the ratio between short term QTe, QTp, Te variability RR (STVQTe/RR, STVQTp/RR and STVTe/RR increased. During exerciserecovery QTpSD (p<0.05), QTpVI (p<0.05), QTeVN (p<0.05), QTpVN (p<0.001), TeVN (p<0.05), STVQTe/RR (p<0.05), STVQTp/RR (p<0.001) and STVTe/RR (p<0.001) were significantly higher in comparison with the rest. The slope between QTe (0.24±0.06) or QTp (0.17±0.06) and RR were significantly higher than Te (0.07±0.06, p<0.001). Conclusion: Heart rate and sympathetic activity, obtained during exercise, seem able to influence the time domain markers of myocardial repolarization dispersion in healthy subjects whereas they do not alter any spectral components.