Circadian rhythms of frequency domain measures of heart rate variability in healthy subjects and patients with coronary artery disease. Effects of arousal and upright posture.

BACKGROUND: Altered neural regulation of the cardiovascular system may be an important factor for various manifestations of ischemic heart disease. This research was designed to compare the circadian rhythm of cardiac neural regulation and autonomic responses to arousal and upright posture between patients with uncomplicated coronary artery disease (CAD) and age-matched subjects with no evidence of heart disease. METHODS AND RESULTS: Twenty-four-hour heart rate variability (HRV) in the frequency domain was analyzed in 20 male patients (mean age, 52 +/- 7 years) with angiographic evidence of CAD without prior myocardial infarction and in 20 healthy men (mean age, 51 +/- 8 years) with no clinical, echocardiographic, or exercise ECG evidence of heart disease. None of the 24-hour average frequency-domain components of HRV differed significantly between the two groups. Healthy subjects had a significant circadian rhythm of normalized units of high-frequency (HF) power of HRV with higher values during sleep. Normalized units of low-frequency (LF) power and the LF/HF ratio also showed a significant circadian rhythm in healthy subjects, with higher values during the daytime. No significant circadian rhythms in any of the normalized spectral components of HRV were observed in patients with CAD, and the night-day difference in LF/HF ratio was smaller in the patients with CAD than in the healthy subjects (0.5 +/- 1.4 versus 1.8 +/- 0.7, P < .001). Awakening when in the supine position resulted in a significant increase in the LF/HF ratio (P < .01) in the healthy subjects, but no significant changes in HRV were observed after awakening in patients with CAD. Assumption of upright position resulted in a comparable decrease in the components of HRV between the groups. CONCLUSIONS: The circadian rhythm of cardiac neural regulation is altered in patients with uncomplicated CAD. Reduced autonomic responses to sleep-wake rhythm suggest that the modulation of cardiac autonomic function by stimuli from the central nervous system is impaired in CAD.