To better understand the pathogenesis of postoperative atrial fibrillation (AF), the mode of onset of AF after coronary artery bypass grafting was analyzed with respect to the autonomic balance, the heart rate (HR), and the presence of arrhythmias preceding the onset of sustained AF.
Method: Holter recordings of 24 hours, obtained from the first postoperative morning until clinically documented sustained AF, were analyzed in 29 untreated patients and in 13 patients treated with thoracic epidural anesthesia (TEA), who all developed AF after coronary artery bypass grafting. The presence of arrhythmias, the HR, and the autonomic balance, assessed by heart rate variability in the frequency domain, were analyzed at predefined time intervals within the 3-hour period before AF onset. Supraventricular premature beats (SPBs) and ventricular premature beats triggering the onset of AF were also evaluated.
Result: An SPB triggering the onset of AF can be identified in 21 (72.4%) of 29 untreated patients and in 12 (100%) of 12 TEA-treated patients in whom the recordings permitted such an analysis. The heart rate variability components analyzed during 5-minute periods for 30 minutes before AF onset did not differ significantly from those at corresponding times at the first postoperative day in either patient group. The HR during the 8 beats immediately before AF onset was lower in TEA-treated than in untreated patients.
Conclusion: The finding of an SPB at the onset of postoperative AF in most of the patients and irrespective of changes in HR supports the hypothesis that postoperative AF is primarily triggered by latent focal atrial activity. The autonomic tone did not seem to be of major importance in the population studied.