A time-related parametric risk factor analysis for postoperative atrial fibrillation after heart surgery

Abstract

Objectives: Multiple mechanisms may be involved in postoperative atrial fibrillation. Therefore, our objective was to determine the risk factors for postoperative atrial fibrillation as a function of time after coronary artery bypass grafting or valve surgeries to determine which risk factors might predominate at different times.

Methods: Parametric hazard functions were determined for 1583 patients and then in subgroups (coronary artery bypass grafting alone, mitral valve procedure, and aortic valve replacement +/- coronary artery bypass grafting). Multivariable risk factor analyses were performed, and the risk for postoperative atrial fibrillation was estimated.

Results: The risk for postoperative atrial fibrillation for all patients was highest immediately postoperatively and at 48 hours. The initial peak risk declined to approximately zero within 18 hours postoperatively. A second peak occurred at 48 hours, followed by a slow decline over the following 4 to 7 days. The time intervals encompassing these peaks were termed phase I and phase II. Predominant risk factors in phase I were older age (relative risk [RR], 1.6; P = .006), longer crossclamp time (RR, 1.3; P = .001), and mitral valve procedure (RR, 2.5; P = .0001). In phase II, these were older age (RR, 3.0; P < .0001), greater weight (RR, 1.6; P < .0001), and Caucasian race (RR, 2.5; P = .006). For patients receiving a mitral valve procedure, the risk for postoperative atrial fibrillation in phase II was higher and remained elevated for as long as 9 days postoperatively in comparison with isolated coronary artery bypass grafting, for which the risk returned to near baseline by postoperative day 6.

Conclusions: Phase I and phase II periods are associated with distinct risk factors; therefore, it is likely that the mechanisms of postoperative atrial fibrillation change over time.