Circadian rhythm of the QT interval dispersion in healthy subjects. Correlation with heart rate variability circadian pattern.

Circadian variation of QT interval dispersion (QTd) and heart rate variability spectral indices was evaluated in healthy persons in 24-hour 3-lead electrocardiogram. Mean values, SD, and SD/mean were evaluated for 24 hours, each hour separately and in night, day, and morning periods. Table Curve 2D and multiple regression were applied to find correlations between parameters. In 50% of subjects, a significant negative correlation was revealed between QTd and HF. Also, in 50% of persons, a significant positive correlation was found between QTd and low frequency/high frequency. After adjustment for periods, correlations were only observed during morning hours. With Table Curve 2D, 2 models of correlations between QTd and HF were found. Multiple regression analysis revealed relations between mean QTd and R-R as well as mean QTd and HF. It is possible that it is sympathovagal balance, as reflected in heart rate variability, and not the tone of both autonomic components that affects QTd variability.