A case of sinus arrest and vagal overactivity during REM sleep.

A young man presented with tachycardia and faintness after an episode of influenza. He underwent 24-h heart rate recordings, each of which documented episodes of sinus arrest lasting up to 7.2 seconds. All episodes occurred in the second half of the night and were always accompanied by severe bradycardia. Cardiac function tests failed to disclose anything abnormal. Two polysomnographic recordings demonstrated that the sinus arrests occurred during REM sleep. Power spectral analysis of heart rate variability showed that during the second half of the night there was an abnormal prevalence of vagal activity, particularly during REM sleep stages, presumably responsible for the bradycardia and fall in blood pressure. We speculate that the episodes of sinus arrest are linked to a central mechanism that triggers the autonomic imbalance during REM sleep.