Circadian variation of QT interval dispersion: correlation with heart rate variability.
The circadian variation of QT interval dispersion and its correlation with heart rate variability (HRV) was examined in 17 normal subjects by using 24-hour recordings of three-lead electrocardiograms. Measurements of HRV, R-R intervals, and QT intervals were made for the first 6 minutes of each hour over a 24-hour period. Spectral analysis of HRV yielded low-frequency power (LF) (0.04-0.15 Hz), high-frequency power (HF) (0.15-0.40 Hz), and the ratio of LF to HF (LF/HF). A rate-corrected QT interval (QTc) was calculated by Bazett's formula, and QT and QTc dispersion was defined as the difference between the maximum and minimum values in any two leads. High-frequency power and QT interval were greater at night than during the day: conversely, LF/HF and dispersion of QT and QTc were greater during the day. The QTc interval remained virtually unchanged throughout the 24-hour period. The dispersion of QTc showed a significant negative correlation with HF and a significant positive correlation with LF/HF. The results suggest that an increased sympathetic tone or a decreased vagal tone increases QT dispersion in healthy subjects.
Ishida
S
S
Department of Laboratory Medicine, Oita Medical University, Japan.
Nakagawa
M
M
Fujino
T
T
Yonemochi
H
H
Saikawa
T
T
Ito
M
M
D000328:Adult; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000517:prevention & control; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory / Q000706:statistics & numerical data; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D013997:Time Factors