Association of body mass index with new-onset atrial fibrillation after coronary artery bypass grafting operations.

BACKGROUND: Postoperative atrial fibrillation (AF) frequently complicates coronary artery bypass grafting (CABG) operations. As the frequency of obesity has increased in the United States, the number of obese patients undergoing CABG has kept pace. This study sought to define the association between body mass index (BMI) and postoperative AF.
METHODS: We studied 12,367 consecutive patients with no history of AF who underwent isolated CABG operations. BMI was stratified according to Centers for Disease Control and Prevention criteria, and differences in baseline clinical and operative characteristics were adjusted through multivariate logistic regression models.
RESULTS: The unadjusted incidence of new-onset postoperative AF demonstrated a U-shape with regard to BMI. The highest incidence (34%) was found in the "lean" stratum (BMI<18.5 kg/m2), followed by 32% in the "severely obese" (BMI≥40 kg/m2) stratum. Lower incidences were found in the "normal" stratum (30%), in the "obese" stratum (28%), and the lowest incidence (26%) was in the overweight stratum. Observed incidence was 50% greater than the expected incidence in the "severely obese" stratum (32% vs 21%). In multivariate regression analysis adjusted for age and other covariates, BMI remains a strong risk factor for new-onset postoperative AF. Compared with normal BMI, obesity (odds ratio, 1.24; 95% confidence interval, 1.08 to 1.42) and severe obesity (odds ratio, 2.00; 95% confidence interval, 1.54 to 2.57) both emerged as strong risk factors for postoperative AF. No association was found between a lean BMI and postoperative AF (odds ratio, 1.14; 95% confidence interval, 0.66 to 1.98).
CONCLUSIONS: After adjusting for potential confounders, obesity, as reflected by the body mass index, remains an independent predictor of postoperative AF.