Obesity Subphenotypes in Atrial Fibrillation: A Linked Electronic Health Record Study in the United Kingdom

Atrial fibrillation (AF) and obesity are increasingly prevalent and interrelated, but how body mass index (BMI) influences cardiovascular outcomes and mortality in AF patients at a population level remains uncertain.

This study aimed to assess cardiovascular hospitalizations and mortality among AF patients by BMI.

Using linked Clinical Practice Research Datalink, Hospital Episodes Statistic, and Office for National Statistics data, we identified 71,519 adults with newly diagnosed AF (1998-2016) and a BMI measure within 12 months of diagnosis. Patients were grouped by World Health Organization BMI categories: underweight, normal weight, overweight, and obese. Primary outcome was all-cause mortality; secondary outcomes were hospitalizations for heart failure (HF), myocardial infarction, ischemic stroke, and bleeding.

The mean age was 74.9 ± 11.3 years; 44.9% were females. Over the median follow-up 5.72 years, 32,198 patients (45.0%) died. After multivariable adjustment, underweight was associated with higher all-cause mortality (HR: 1.87; 95% CI: 1.77-1.96), whereas overweight (HR: 0.72; 95% CI: 0.70-0.74) and obese (HR: 0.69; 95% CI: 0.67-0.71) categories had lower mortality vs normal weight. Obesity was independently associated with increased HF hospitalization risk, whereas overweight was modestly protective. Obesity was associated with lower adjusted myocardial infarction and bleeding hospitalization and showed no significant adjusted association with ischemic stroke. Cause-specific mortality analysis showed higher circulatory and neoplasm deaths among obese patients and higher respiratory deaths in underweight patients.

In this large, nationwide AF cohort, being underweight at the time of AF diagnosis was associated with higher mortality, whereas being overweight and obese were paradoxically associated with lower all-cause mortality despite increased HF hospitalizations in obese patients.