Risk of new-onset atrial fibrillation in relation to body mass index

Background: Obesity is associated with increased risk of atrial fibrillation (AF), but it is unknown whether the association differs by duration or persistence of AF. It is also unknown to what extent cardiovascular risk factors may mediate this association. Methods: This population-based case-control study included 425 subjects with new-onset AF and 707 controls. The AF cases were identified through International Classification of Diseases, Ninth Revision codes for inpatient and outpatient visits and verified by medical record review. Medical records provided data on height, weight, and cardiovascular risk factors. Results: On average, AF risk was 3% higher (95% confidence interval [CI], 1%-5%) per unit increment in body mass index (BMI) ( calculated as weight in kilograms divided by height in meters squared). For sustained AF ( duration >= 6 months), risk was higher by 7% (95% CI, 3%-11%) per unit BMI increment; for intermittent AF ( duration >= 8 days or recurrent), 4% ( 95% CI, 1%-6%); and for transitory AF ( duration < 8 days), 1% ( 95% CI, -1% to +4%). Compared with those with normal BMI, the odds ratios for overweight and obese subjects were as follows: overweight, 0.97 ( 95% CI, 0.68-1.38); obese class 1,1.18 ( 95% CI, 0.80-1.73); obese class 2, 1.34 ( 95% CI, 0.82-2.18); and obese class 3, 2.31 ( 95% CI, 1.36-3.91) (P = .002 for trend). When diabetes mellitus, a possible mediator, was added to the model, the odds ratio per unit increment of BMI decreased from 1.034 to 1.028. Adjustment for other cardiovascular risk factors including hyperlipidemia and blood pressure did not attenuate the BMI-AF association. Conclusions: The association with BMI was stronger for sustained AF than for transitory or intermittent AF. The obesity-AF association appears to be partially mediated by diabetes mellitus but minimally through other cardiovascular risk factors.