Obesity and risk of new-onset atrial fibrillation after cardiac surgery

Background - New-onset postoperative atrial fibrillation (AF) is a common complication of cardiac surgery that has substantial effects on outcomes. In the general ( nonsurgical) adult population, AF has been linked to increasing obesity, which correlates with left atrial enlargement. It is not known whether postoperative AF is similarly linked to obesity. Methods and Results - This was a retrospective analysis of the incidence of AF in terms of body mass index (BMI). A total of 8051 consecutive cardiac surgery patients (1994 to 2004; mean age 64 [SD 11] years; 5372 men [67%]) who were free of any history of preoperative AF or flutter were included in the analysis. This series included 3164 obese patients (39%; median age 62 years) and 4887 nonobese patients (61%; median age 66 years), who were further divided on the basis of BMI (kg/m(2)) into 6 groups: BMI < 22 kg/m(2), 22 <= BMI <= 25 kg/m(2) (normal), 25 < BMI >= 30 kg/m(2) (overweight), 30 <= BMI <= 35 kg/m(2) (obese I), 35 <= BMI >= 40 kg/m(2) (obese II), and BMI > 40 kg/m(2) (obese III). Unadjusted AF incidence was similar in obese and nonobese patients (n = 742 [23.5%] versus n = 1068 [21.9%], respectively; P = 0.099). Covariate-adjusted ORs for AF were systematically greater for larger patients than for patients in the normal group (adjusted OR [95% CI] = 1.18 [1.00 to 1.40], 1.36 [1.14 to 1.63], 1.69 [1.35 to 2.11], and 2.39 [1.81 to 3.17] for overweight, obese I, obese II, and obese III, respectively). Other AF predictors included age (adjusted OR = 1.52 [ 95% CI 1.46 to 1.58] per 10 years), mitral valve surgery (adjusted OR = 2.42 [ 95% CI 1.92 to 3.06]), aortic valve surgery (adjusted OR = 1.79 [95% CI 1.45 to 2.22]), chronic obstructive pulmonary disease (adjusted OR = 1.28 [95% CI 1.12 to 1.46]), male gender (adjusted OR = 1.24 [95% CI 1.10 to 1.40]), preoperative beta-blocker use (adjusted OR = 1.17 [95% CI 1.05 to 1.32]), vascular disease (adjusted OR = 1.18 [95% CI 1.05 to 1.32]), white race (adjusted OR = 1.33 [95% CI 1.07 to 1.66]), history of arrhythmia other than AF/flutter (adjusted OR = 0.80 [95% CI 0.68 to 0.96]), ejection fraction < 40% (adjusted OR = 1.16 [95% CI 1.03 to 1.31]), left main disease (adjusted OR = 1.15 [95% CI 1.00 to 1.32]), and off-pump surgery (adjusted OR = 0.61 [95% CI 0.44 to 0.83]). The obesity-AF association was confirmed in 4 1-to-1 propensity-matched obese versus nonobese comparisons and in 2 separate derivation/validation subcohort analyses. Conclusions - Obesity is an important determinant of new-onset AF after cardiac surgery. Future postoperative AF risk models should incorporate BMI or obesity levels. Studies examining the efficacy of AF-minimizing prophylactic interventions in high- BMI patients, particularly in the elderly, may be warranted.