Relation of autonomic modulation to recurrence of atrial fibrillation following cardioversion

The aim of this study was to investigate the time course of changes in autonomic nervous system activity in patients with long-standing atrial fibrillation (AF) following internal electrical conversion to sinus rhythm and to look for differences between patients who do and do not relapse. Time-domain indexes of heart rate variability were calculated from 24-hour Holter recordings on the day of conversion and 1 day and 1 month afterward for 22 patients with chronic (>3 months) AF. Ten healthy subjects served as a control group. During the day of cardioversion the mean RR interval and its circadian variation differed significantly between controls and patients. The mean values of successive RR intervals that deviated by >50% from the prior RR interval and the root-mean-square of successive RR interval differences—indexes of vagal modulation—were initially significantly higher in patients than in controls but showed a decrease (p