Background: Obesity increases risk of atrial fibrillation (AF) at least in part due to pro-inflammatory effects, but has been paradoxically associated with improved mortality. Although statins have pleiotropic anti-inflammatory properties, their interaction with obesity and clinical outcomes in AF is unknown. We explored the relationship between BMI, statin use, and all-cause mortality and AF/congestive heart failure (CHF)-related encounters, hypothesizing that statin exposure may be differentially associated with improved outcomes in overweight/obesity.

Methods: This was a single center retrospective cohort study of adults with AF diagnosed between 2011-2018. Patients were grouped by body mass index (BMI) and statin use at time of AF diagnosis. Outcomes included all-cause mortality and ED or inpatient encounters for AF or CHF.

Results and conclusions: A total of 2503 subjects were included (median age 66 years, 43.4 % female, median BMI 29.8 kg/m2, 54.6 % on baseline statin therapy). Increasing BMI was associated with decreased mortality hazard but not associated with AF/CHF encounter risk. Adjusting for statin-BMI interaction, demographics, and cardiovascular comorbidities, overweight non-statin users experienced improved mortality (adjusted hazard ratio [aHR] 0.55, 95 % CI 0.35-0.84) compared to statin users (aHR 0.98, 95 % CI 0.69-1.40; interaction P-value = 0.013). Mortality hazard was consistently lower in obese non-statin users than in statin users, however interaction was insignificant. No significant BMI-statin interactions were observed in AF/CHF encounter risk. In summary, statin use was not differentially associated with improved mortality or hospitalization risk in overweight/obese groups. These findings do not support statins for secondary prevention of adverse outcomes based on overweight/obesity status alone.