Factors Associated with Atrial Fibrillation in Heart Failure with Preserved and Mildly Reduced Ejection Fraction: A Real-World Cohort Study

Background: Atrial fibrillation (AF) frequently coexists with heart failure (HF) and worsens clinical outcomes. However, factors associated with AF in HF with preserved (HFpEF) and mildly reduced ejection fraction (HFmrEF) remain poorly defined. This study aimed to identify clinical, laboratory, and echocardiographic determinants of AF in these HF phenotypes. Methods: This retrospective single-center observational study included 700 consecutive patients with HF hospitalized between January 2018 and December 2023. The median age was 74 years (IQR 66–80). Women predominated in the cohort (55.3% vs. 44.7%, p < 0.001). Based on echocardiographically assessed left ventricular ejection fraction, patients were stratified into groups with preserved (≥50%), mildly reduced (41–49%), and reduced (≤40%) ejection fraction. Determinants of AF were evaluated using univariate and multivariate logistic regression analyses, and model discrimination was assessed using ROC analysis. Results: Strongest determinants of AF in our patients with HFpEF and HFmrEF were left atrial size (OR 1.114 per mm increase; 95% CI 1.054–1.177; p < 0.001), moderate and severe tricuspid regurgitation (OR 4.092; 95% CI 1.977–8.466; p < 0.001 and OR 6.957; 95% CI 2.482–19.499; p < 0.001), male gender (OR 1.680; 95% CI 1.076–2.621; p = 0.022) and advanced age (OR 1.070 per year; 95% CI 1.032–1.109; p < 0.001). Conclusions: In patients with HFpEF and HFmrEF, AF is strongly associated with atrial remodeling, with left atrial enlargement as the key structural determinant. The identified associations may contribute to an improved understanding of AF in HFpEF and HFmrEF; however, their potential role in risk stratification requires validation in prospective studies.