BACKGROUND AND PURPOSE The influence of body mass index (BMI) on clinical outcomes in patients with atrial fibrillation remains controversial, especially among Asians. We aimed to evaluate the association between BMI and clinical outcomes in Asian patients with atrial fibrillation receiving oral anticoagulants.

METHODS Using the Korean National Health Insurance database between January 2015 and December 2017, we identified oral anticoagulant new users among patients with nonvalvular atrial fibrillation who had BMI information. We analyzed ischemic stroke, intracranial hemorrhage, hospitalization for gastrointestinal bleeding, major bleeding, all-cause death, and the composite clinical outcome according to BMI categories.

RESULTS A total of 43 173 patients were included across BMI categories (kg/m²): underweight (<18.5) in 3%, normal (18.5 to <23) in 28%, overweight (23 to <25) in 24%, obese I (25 to <30) in 39%, and obese II (≥30) in 6%. Higher BMI (per 5 kg/m² increase) was significantly associated with lower risks of ischemic stroke (hazard ratio [HR], 0.891 [95% CI, 0.801-0.992]), hospitalization for gastrointestinal bleeding (HR, 0.785 [95% CI, 0.658-0.937]), major bleeding (HR, 0.794 [95% CI, 0.686-0.919]), all-cause death (HR, 0.658 [95% CI, 0.605-0.716]), and the composite clinical outcome (HR, 0.751 [95% CI, 0.706-0.799]), except for intracranial hemorrhage (HR, 0.815 [95% CI, 0.627-1.061]). The underweight group was associated with an increased risk of composite clinical outcome (HR, 1.398 [95% CI, 1.170-1.671]), mainly driven by an increased risk of all-cause death. The effects of non-vitamin K antagonist oral anticoagulant versus warfarin on clinical outcomes were similar across BMI groups.

CONCLUSIONS Higher BMI was independently associated with a lower risk of ischemic stroke, major bleeding, and better survival. Underweight patients had a higher risk of all-cause death and composite clinical outcome. The optimal BMI for patients with atrial fibrillation should be defined and managed according to an integrated care pathway.