Competing autonomic mechanisms precede the onset of postoperative atrial fibrillation

OBJECTIVES This study was designed to evaluate autonomic changes preceding atrial fibrillation/flutter (AF) after thoracotomy. BACKGROUND Autonomic fluctuations before the onset of postoperative AF have been reported but with conflicting results. METHODS In 48 patients with postoperative AF, 2-h Holier recordings before the onset of AF were compared with corresponding data from 48 age- and gender-matched surgical controls without AF. Five-minute segments of heart rate variability (HRV) were studied using linear regression methods. RESULTS There was a near-significant trend for the RR interval among patients with AF to be lower than controls (p = 0.06), whereas the standard deviation of RRs (p < 0.0001), root mean square of successive RR differences (p < 0.0001), proportion of RRs >50 ms different (p < 0.0001), low-frequency power (p = 0.0003) and its log (p < 0.0001), and high-frequency-power (p < 0.0001) and its log (p < 0.0001) were all significantly greater in patients with AF, respectively. In comparison to controls, AF patients had a significant decrease in RR interval (p = 0.02) and significant increments in all time- and frequency-domain analyses studied. CONCLUSIONS In the period before the onset of postoperative AF, there are significant increases in HRV during a time when heart rate also increases. These novel findings are consistent with parasympathetic resurgence competing with increasing sympathetic activity as the triggering mechanism for postoperative AF. (C) 2003 by the American College of Cardiology Foundation.