ANALYSIS OF FREQUENCY-DEPENDENCY OF VENTR ICULAR DEPOLARIZATION BY HALTER MONITORING IN YOUNG-ADULTS

Adaptation of ventricular repolarization duration to heart rate provid es additionnal information to the static duration of QT interval. Meth ods : QT/RR relation and his slope were determined using 24-hour ECG r ecordings from 17 young male normal volunteers (mean age : 22 +/- 3 ye ars). In order to determine the influence of the autonomic nervous sys tem on the rate-dependance of RT, the authors compared the slopes obta ined from recordings during the day and the night. Then, the respectiv e rate-dependences of the entire QT interval (QTe) and its initial sub division (QTa) and their correlations with parameters of heart rate va riability were studied. Results : the QTa/RR and QTe/RR relations were constantly linear, with very significant regression coefficients. The daytime QTa/RR and QTe/RR slopes were significantly steeper than the nightime ones (0.138 +/- 0.035 vs 0.108 +/- 0.040, p < 0.05 for QTe/RR , 0.160 +/- 0.069 vs 0.108 +/- 0.055, p < 0.01 for QTa/RR). The early part of QT showed a stronger rate-dependence than the global QT, but o nly at daytime (0.160 +/- 0.069 vs 0.138 +/- 0.035, p < 0.05). No corr elation was found between rate dependences and heart rate variability parameters. Conclusion : the authors demonstrate, from ambulatory ECG recordings, the influence of the autonomic nervous system on the rate- dependence of ventricular repolarization in normal young adults, and a difference in rate-dependence between the entire QT interval and its initial part QTa, due to differences in autonomic nervous system tone. This heterogeneity should be taken to acount in the study of patholog ical changes or drugs effects on ventricular repolarization.