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 auto nomic nervous system activity in patients with long-standing atrial fibrill ation (AF) following internal electrical conversion to sinus rhythm and to look for differences between patients who do and do not relapse. Time-domai n indexes of heart rate variability were calculated from 24-hour Halter rec ordings on the day of conversion and 1 day and 1 month afterward for 22 pat ients with chronic (>3 months) AF. Ten healthy subjects served as a control group. During the day of cardioversion the mean RR interval and its circad ian variation differed significantly between controls and patients. The mea n values of successive RR intervals that deviated by >50% from the prior RR interval and the root-mean-square of successive RR interval differences-in dexes of vagal modulation-were initially significantly higher in patients t han in controls but showed a decrease (p <0.05) by the second day(from 12.4 +/- 7% to 8.1 +/- 5% to 7.3 +/- 5% and from 49 +/- 9 to 39 +/- 12 to 41 +/ - 11 ms, respectively) to levels similar to those of the controls (7.6 +/- 5% and 40 +/- 17 ms, respectively). Only these 2 indexes contained signific ant prognostic information about relapse: patients who later relapsed had h igher initial values than those who did not, and these values remained high during the 2 days after conversion. In conclusion, this study provides dat a confirming that spontaneous chronic AF in humans results in a significant increase in vagal tone that is reversed with time after restoration of sin us rhythm. Persistently higher values of vagal tone are observed in patient s who relapse, and are probably a predictor for recurrence. (C)2000 by Exce rpta Medica, Inc.