Atrial Fibrillation as a Marker of High-Risk Phenotype in Acute Coronary Syndrome

Background: Atrial fibrillation (AF) is frequently encountered in patients presenting with acute coronary syndrome (ACS); however, its clinical significance beyond being a simple rhythm disturbance remains debated. We hypothesized that AF at presentation may be associated with a high-risk clinical profile characterized by hemodynamic instability and increased inflammatory and ischemic activity. Methods: This single-center, retrospective observational study included consecutive adult patients with acute coronary syndrome admitted to a tertiary cardiology center between January 2022 and December 2024. Patients were classified into two groups according to cardiac rhythm at presentation: AF and sinus rhythm. Baseline demographic characteristics, hemodynamic parameters, laboratory biomarkers, validated risk scores, and revascularization strategies were compared between groups. Multivariable logistic regression analysis was performed to evaluate whether AF was independently associated with a high-risk presentation, primarily defined by elevated GRACE risk score, reduced left ventricular ejection fraction, and increased inflammatory markers. Results: A total of 158 patients were included, of whom 50 (31.6%) presented with atrial fibrillation (mean age 71.2 ± 11.4 years, 46% female). Compared with patients in sinus rhythm, those with AF had significantly higher GRACE risk scores, lower left ventricular ejection fraction, faster heart rate, and higher white blood cell counts and peak high-sensitivity troponin levels. These associations remained significant after multivariable adjustment. Patients with AF also showed a numerically higher prevalence of severe angina at presentation. Conclusions: In patients presenting with ACS, atrial fibrillation is associated with a high-risk hemodynamic profile accompanied by increased inflammatory and ischemic activity. Rather than being an incidental finding, AF may represent a clinically relevant marker of acute cardiovascular stress and may contribute to early risk stratification in this setting.