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) electrocardiogram (ECG) analysis (time and frequency domain) have been obtained in 21 healthy volunteers during the following conditions: free breathing (rest); controlled breathing (resp); the first 5 minutes of postexercise recovery phases (exercise ), maximum sympathetic activation; and during the second 5 minutes of postexercise recovery phases (exercise ), intermediate sympathetic activation. Finally, we analyzed the whole repolarization (QTe), the QT peak (QTp), and T peak - T end intervals (Te).

Results: During the exercise , major part of repolarization variables changed in comparison to the rest and resp conditions. Particularly, QTe, QTp, and Te standard deviations (QTe , QTp , and Te ); variability indexes (QTeVI and QTpVI), normalized variances (QTeVN, QTpVN, and TeVN); and the ratio between short-term QTe, QTp, and Te variability RR (STV , STV and STV ) increased. During exercise , QTp (P < .05), QTpVI (P < .05), QTeVN (P < .05), QTpVN (P < .001), TeVN (P < .05), STV (P < .05), STV (P < .001), and STV (P < .001) were significantly higher in comparison to 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 < .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.