Prognostic Significance of New-Onset Atrial Fibrillation Burden in Acute Myocardial Infarction Patients: A Comparison Based on Left Ventricular Ejection Fraction.

Acute myocardial infarction (AMI) with reduced or preserved left ventricular ejection fraction (LVEF) is associated with distinct prognoses and differing risk factor profiles. However, the use of new-onset atrial fibrillation (NOAF) burden in risk stratification of AMI patients, particularly across LVEF subgroups, remains unclear. We analyzed consecutive AMI patients without prior AF who developed their first in-hospital AF episode between 2014 and 2022. The patients were stratified by LVEF (AMIrEF: <40%; AMIpEF: ≥40%) and AF burden (>10.87% vs. ≤10.87%). The primary endpoint was a major adverse cardiovascular event (MACE), including cardiovascular death and heart failure hospitalization. Among 644 patients with LVEF data, 178 (27.6%) were AMIrEF and 466 (72.4%) were AMIpEF; 248 (38.5%) had a high AF burden. Over a median follow-up time of 4.2 years, the MACE incidence was 18.9 and 23.0 per 100 person-years in low- and high-burden AMIrEF patients, and 7.2 and 17.5 in AMIpEF patients, respectively. After multivariable adjustment, a high NOAF burden was significantly associated with increased MACE in AMIpEF patients [hazard ratio (HR): 2.63, 95% confidence interval (CI): 1.82-3.79], but not in AMIrEF patients [HR: 1.29, 95% CI: 0.79-2.10]. Propensity-matched analysis yielded concordant results [AMIrEF: 1.15 (0.69-1.90); AMIpEF: 2.45 (1.75-3.45)]. In conclusion, a high NOAF burden is strongly associated with adverse long-term cardiovascular outcomes in AMIpEF patients, highlighting its potential utility for risk stratification in this population.