Autonomic control in patients experiencing atrial fibrillation after cardiac surgery

Atrial fibrillation (AF) occurs in 20-40% of patients after open heart surgery and leads to an increased morbidity and prolonged hospital stay. Earlier studies have demonstrated that depressed baroreflex function predicts mortality and major arrhythmic events in patients surviving myocardial infarction. Cardiac surgery per se leads to decreased baroreflex sensitivity (BRS) and heart rate variability (HRV). Hence, the present study was aimed at analyzing the impact of the cardiovascular autonomous system on the development of postsurgical AF.

The study covered 51 patients who consecutively underwent aortic valve replacement, coronary artery bypass surgery, or combined procedures. Noninvasive blood pressure and ECG were recorded the day before and 24 hour after surgery. BRS, linear as well as nonlinear HRV parameters were calculated using established methods. Eighteen patients developed AF during the first postoperative week, while 33 remained in sinus rhythm (SR) throughout the observation period. Patients with postoperative (PostOp) AF exhibited a significantly reduced preoperative (PreOp) BRS in terms of bradycardic and tachycardic regulation (average delayed slope [ms/mmHg]: SR: PreOp: 9.83 +/- 3.26, PostOp: 6.02 +/- 2.29, Pre-Post: P < 0.001; AF: PreOp: 7.59 +/- 1.99, PostOp: 6.39 +/- 3.67, Pre-Post: P < 0.044; AF vs SR: PreOp: P < 0.01, PostOp: ns). In both groups, surgery caused a decrease of BRS and HRV. Analysis of nonlinear dynamics revealed a tendency toward decreased system complexity caused by the operation; this trend was significant in patients remaining in sinus rhythm.

Patients experiencing postoperative AF obviously suffer from an impaired BRS before surgery already. These findings may be used to guide prophylactic antiarrhythmic therapy.