Prognostic Impact of New‐Onset Atrial Fibrillation After Cardiac Arrest: Observations From a Federated Research Network

BACKGROUND: Data on adverse events in patients developing atrial fibrillation (AF) after cardiac arrest (CA) are limited. METHODS: Retrospective analysis using the TriNetX network. Adults (≥ 18 years) with CA (ICD-10-CM I46) from 2014 to 2024 were divided into two cohorts: those with new-onset AF (I48) within 2 days after CA and those without. Primary outcome was the 1-year risk of a composite of all-cause death, stroke, acute myocardial infarction (AMI), and recurrent CA. Secondary outcomes were the individual components. Cox regression provided hazard ratios (HRs) and 95% confidence intervals (CIs) before and after 1:1 propensity score matching (PSM). Sensitivity analyses stratified follow-up into early (3-33 days) and late (34-367 days) phases; subgroups included age, sex, hypertension, diabetes, heart failure, and shockable rhythms. RESULTS: We identified 1221 patients with post-CA AF (mean age 65 ± 14.9 years; 33.8% female) and 149 222 without AF (57.9 ± 17.6 years; 39.3% female). Before PSM, AF patients were older and had greater cardiovascular burden. After PSM post-CA AF was associated with higher risk of the composite outcome (HR 1.25, 95% CI 1.13-1.38), AMI (HR 1.59, 95% CI 1.30-1.95), recurrent CA (HR 1.48, 95% CI 1.30-1.70), and a non-significant trend toward increased stroke risk, which was greater during the early phase post-CA. Female patients showed stronger association between post-CA AF and stroke (p for interaction = 0.04). CONCLUSION: Post-CA AF is associated with an increased risk of adverse events, including AMI and recurrent CA. Stroke risk was higher during the early post-resuscitation phase and among female patients.