Timing of New-Onset Atrial Fibrillation After Myocardial Infarction: Prognostic Impact and Associated Clinical Characteristics.

BACKGROUND: Atrial fibrillation (AF) commonly complicates myocardial infarction (MI) and is associated with adverse outcomes. However, the prognostic significance of AF timing after MI remains incompletely understood. METHODS: We conducted a retrospective cohort study of 3390 patients with myocardial infarction, stratified by MI subtype (NSTEMI and STEMI). AF was categorized as early (during index hospitalization), late (after discharge), or absent. Clinical, echocardiographic, and angiographic data were collected. Outcomes were assessed using Kaplan-Meier analyses and log-rank testing. The association between AF timing and outcomes was evaluated using multivariable time-dependent Cox proportional hazards models with pairwise comparisons, adjusting for relevant demographic and clinical covariates. Predictors of late AF were evaluated using multivariable logistic regression. RESULTS: Among patients with myocardial infarction, AF developed in 451 patients (13.3%), 114 with STEMI and 337 with NSTEMI, occurring as early AF in 249 and late AF in 202. Kaplan-Meier analyses demonstrated significant in long-term major adverse cardiovascular events (MACE), defined as recurrent myocardial infarction with or without repeat revascularization, stroke, and all-cause mortality, according to AF timing, with late AF associated with the poorest outcomes (p<0.001). In multivariable time-dependent Cox models, late-onset AF was independently associated with an increased risk of MACE (HR: 1.5 [1.0-2.2], p=0.044, HR: 2.4 [1.1-5.3], p=0.032 in NSTEMI and STEMI, respectively). In contrast, early AF was not consistently associated with long-term MACE after adjustment (HR: 0.7 [0.4-1.0], p=0.060, HR: 1.3 [0.8-2.3], p=0.327 in NSTEMI and STEMI, respectively). Pairwise comparisons confirmed higher risk with late AF compared with no AF. In contrast, the late versus early AF comparison did not reach statistical significance in STEMI, likely due to limited event numbers. In multivariable logistic regression, older age and diabetes mellitus were independently associated with the development of late AF. CONCLUSION: AF timing after myocardial infarction is prognostically relevant. Late-onset, but not early, AF was independently associated with adverse outcomes in time-dependent analyses, supporting a temporal classification of AF.