The 'obesity paradox' in atrial fibrillation: observations from the ARISTOTLE (Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation) trial

The prognostic implication of adiposity on clinical outcomes in atrial fibrillation (AF) patients treated with oral anticoagulation is unclear. A total of 17 913 patients in the Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation trial had body mass index (BMI) measured at baseline. For the primary analysis, BMI was categorized as normal (18.5 to < 25 kg/m(2)), overweight (25 to < 30 kg/m(2)), and obese (a parts per thousand yen30 kg/m(2)). Waist circumference (WC) was defined as high if > 102 cm for men and > 88 cm in women. Outcomes were stroke or systemic embolism, a composite endpoint (stroke, systemic embolism, myocardial infarction, or all-cause mortality), all-cause mortality, and major bleeding. Cox models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) across categories of BMI and WC adjusting for established risk factors and treatment allocation. At baseline, 4052 (22.6%) patients had a normal BMI, 6702 (37.4%) were overweight, and 7159 (40.0%) were obese. In multivariable analyses, higher BMI was associated with a lower risk of all-cause mortality [overweight: HR 0.67 (95% CI 0.59-0.78); obese: HR 0.63 (95% CI 0.54-0.74), P < 0.0001] and the composite endpoint [overweight: HR 0.74 (95% CI 0.65-0.84); obese: HR 0.68 (95% CI 0.60-0.78), P < 0.0001] compared with normal BMI. In women, high WC was associated with a 31% lower risk of all-cause mortality (P = 0.001), 27% lower risk of the composite endpoint (P = 0.001), and 28% lower risk of stroke or systemic embolism (P = 0.048) but not in men. There was no significant association between adiposity and major bleeding. In patients with AF treated with oral anticoagulants, higher BMI and WC are associated with a more favourable prognosis.