Determinants and consequences of atrial fibrosis in patients undergoing open heart surgery

Atrial fibrillation (AF) is a frequent complication following open-heart surgery (OHS). Increased atrial fibrosis may indicate the presence of an intrinsic arrhythmogenic substrate. The aim of this prospective study was to determine whether atrial fibrosis is associated with increased prevalence of AF after OHS.

Right atrial appendages were obtained from 259 patients undergoing OHS; none of the patients had a history of AF. Atrial fibrosis was quantitatively analyzed with point counting. All patients were followed prospectively until hospital discharge. None of the patients received anti-arrhythmic prophylaxis. Post-operative AF was defined as an episode of AF lasting > or = 5 min.

Quantitation of atrial fibrosis yielded a mean volume percentage of 15.8 +/- 4.3% (V%; range 4.6-32.4%). Patient age was found to correlate with the amount of atrial fibrosis (r = 0.165; P < 0.01) and surface P-wave duration (r = 0.249; P < 0.01). The degree of fibrosis combined with P-wave duration predicted post-operative AF (P < 0.01). Age (> 60 years) and P-wave duration (> or = 100 ms) were independent predictors of post-operative AF (age: relative risk 2.20; P-wave: relative risk 2.69; P < 0.05). The patients were divided into three groups: group 1, V% = 4.6-13.8%; group 2, V% = 13.9-23.1%; group 3, V% = 23.2-32.4%. A total of 52 patients (20.1%) developed AF, which occurred least commonly in group 1 (16.3%) and group 2 (21.2%) as compared with group 3 (33.3%).

Atrial fibrosis provides a pathophysiological substrate for post-operative AF. The results support the importance of P-wave duration as a predictor of post-operative AF, and explain the increased prevalence of AF in elderly patients after OHS.