Twenty-four-hour pattern of ventricular excitation rhythm in resting normal human subjects

Using a biotelemetry system, the electrocardiogram (ECG) was continuously measured over 24 hr in a given environmental condition in 8 normal human subjects. The frequency of ventricular excitation rhythm (VER) was obtained from inverse of R-R interval of ECG. This study was undertaken to be informed of the variation of VER over 24 hr in resting normal subjects with different ages. The averaged frequency of VER per day (VERd) and its relative coefficient of variation (CV) ranged from 1.44 to 1.01 Hz (mean: 1.24 Hz) and 26 to 10% (mean: 20%) with age of 10 to 73 years (mean: 42 years). VERd and CV showed a tendency to decrease with age. The VERd histogram showed not a normal distribution but a multimodal distribution. Two or three large positive deviations, denoted as L, N, and H modal components, from the normal distribution curve were detected. The mode of L and H modal components was 1.01 and 1.37 Hz, respectively. The frequency distribution of L and H modal components changed with relation to a circadian rhythm and sleep-wakefulness cycles. An hourly histogram of ventricular excitation rhythm (VERh) frequently showed an unimodal distribution and the relative coefficient of variation of VERh ranged from 7.9 to 13.3% which was smaller than that of CV. The mode of VERh histogram changed in association with the circadian rhythm, the sleep-wakefulness cycles and a fluctuation period of 2 to 3 hr.