Circadian variation of heart rate variability and the rate of autonomic change in the morning hours in healthy subjects and angina patients.

BACKGROUND: Incidence of sudden cardiac death peaks during the early morning hours when there is a rapid withdrawal of vagal and an increase of sympathetic tone. The rate of autonomic change could be of prognostic importance. PATIENTS AND METHODS: A total of 65 patients with angina pectoris, free from other diseases and drug free, were Holter monitored for 24 h. A total of 30 patients were also monitored on isosorbide-5-mononitrate (IS-5-MN) and on metoprolol respectively. A total of 33 age-matched healthy subjects served as controls. Spectral components of heart rate variability (HRV) were analysed hourly, with special reference to the rapid changes of autonomic tone during the night and early morning hours. Circadian variation was assessed in two ways: (1) Mean HRV day (8 a.m.-8 p.m.) and night (0-5 a.m.) were compared. (2) For the morning/night hours (0-10 a.m.), individual hourly values for max. and min. HRV, the difference max.-min. (gradient), the rate of change per hour between max. and min. (velocity) and the largest difference between two consecutive hours (max. velocity) were recorded and the mean value for the group calculated.
RESULTS: During the night/morning hours, healthy controls demonstrated faster HF max. velocity (P=0.002) and higher HF gradient (P=0.011) than angina patients. Metoprolol and IS-5-MN increased the HF gradient (P=0.008 and P=0.003, respectively), and metoprolol tended to increase the max. velocity (P=0.02). Metoprolol substantially decreased the LF/HF gradient (P=0.001), velocity (P=0.008) and max. velocity (P=0.0001).
CONCLUSION: Rapid vagal withdrawal seemed to be a sign of a healthy autonomic nervous system in the control group but was significantly slower in angina patients. IS-5-MN and metoprolol tended to normalise vagal withdrawal and metoprolol slowed down the rapid increase in sympathetic predominance in the morning in patients.