Case‐Crossover Analysis of Short‐Term Particulate Matter and Health Outcomes in Patients With Atrial Fibrillation

Background Residents of western US states face elevated fine particulate matter (PM 2.5 ) exposure from increasingly frequent and intense wildfires, raising concerns about cardiovascular risk. Whether short‐term PM 2.5 exposure increases odds of hospitalization or emergency care in patients with established atrial fibrillation (AF) remains unclear. Methods Using 2021 Medicare data, we identified patients with established AF residing in western US states. Zip code–level daily PM 2.5 was estimated using a 1 km 2 geospatial model; high PM 2.5 was defined as ≥9.0 μg/m 3 . Odds ratios (ORs) for all‐cause and cardiovascular disease hospitalization and emergency department visits were estimated using conditional logistic regression at lag 0, 1, and 3 days, adjusting for extreme heat and public holidays. Results The final cohort included 26 158 patients (mean age 79 ± 9.0 years) with established AF. Exposure to high levels of PM 2.5 was associated with 10% (95% CI, 1%–20%) increased odds of hospitalizations for cardiovascular disease. Specifically, high PM 2.5 was associated with 24% (95% CI, 3%–48%) increased odds of hospitalization and 34% (95% CI, 6%–70%) higher odds of emergency department visits for all AF‐related diagnoses. We did not observe significant interaction effects between PM 2.5 and extreme heat on the risk of hospitalization or emergency department visits for cardiovascular disease or AF. Conclusion On days with elevated PM 2.5 levels, patients with AF were associated with higher odds of AF‐related or cardiovascular hospitalizations and emergency department visits, highlighting the need for targeted prevention strategies to protect vulnerable populations from the adverse effects of air pollution.