CIRCADIAN-RHYTHM OF HEART-RATE-VARIABILITY IS REVERSIBLY ABOLISHED INISCHEMIC STROKE

Background and Purpose Acute brain infarction significantly decreases heart rate variability as a result of cardiovascular autonomic dysregu lation. However, information regarding circadian rhythms of heart rate and heart rate variability is limited. Methods In this prospective st udy, we analyzed 24-hour circadian rhythm of heart rate and the time a nd frequency domain measures of heart rate variability in 24 patients with hemispheric brain infarction, 8 patients with medullary brainstem infarction, and 32 age-and sex-matched healthy control subjects. ECG data were obtained from the patients in the acute phase and at 6 month s after the infarction. Results In the acute phase of stroke, all the components of heart rate variability, ie, standard deviation of RR int ervals, total power, high-frequency power, low-frequency power, and ve ry-low-frequency power, were similar at night (from midnight to 6 AM) and during the day (from 9 AM to 9 PM), indicating that the circadian oscillation of heart rate variability had been abolished. At 6 months after brain infarction, the circadian rhythm had returned and, as in t he control subjects, the values at night were significantly higher tha n those in the daytime. The values in hemispheric and in brainstem inf arction did not differ significantly from each other. Conclusions Thes e results suggest that circadian fluctuation of heart rate variability is reversibly abolished in the acute phase of ischemic stroke and tha t it returns during the subsequent 6 months. The loss of the relative vagal nocturnal dominance may contribute to the incidence of cardiac a rrhythmias and other cardiovascular complications after acute stroke.