Nonoptimal Temperature Is Associated With Higher Atrial Fibrillation Hospitalizations in China: A Nationwide Case-Crossover Study

Background: Previous studies have evaluated extreme temperatures' impact on cardiovascular health, but few have specifically focused on atrial fibrillation (AF)-related hospitalizations across a wide temperature range. Objectives: This study aimed to quantify and investigate the association between ambient nonoptimal temperatures and AF hospitalizations. Methods: A two-stage time-stratified case-crossover study was conducted using a nationwide registry of 1,665,014 AF patients from 251 cities between 2014 and 2023. Conditional quasi-Poisson and distributed lag nonlinear models analyzed associations between nonoptimal temperature and AF hospitalizations. Subgroup and attributable burden analyses identified potentially susceptible subpopulations. Results: The minimum hospitalization temperature for AF was 24.3 °C (74th percentile). Compared to the minimum hospitalization temperature over a lag of 0 to 14 days, cumulative relative risks for extreme cold and heat (1st and 99th percentiles) were 1.32 (95% CI: 1.24-1.42) and 1.03 (95% CI: 0.99-1.07), respectively. Hospitalization risks related to extreme temperatures were similar across subgroups of age, sex, and baseline diseases. Overall, 14.3% (95% empirical CI [eCI]: 12.2%-14.8%) of AF hospital admissions were attributable to nonoptimal temperatures, with higher burden in northern China (18.4%; 95% eCI: 15.7%-19.4%) than southern China (12.4%; 95% eCI: 9.6%-13.6%). Conclusions: In this nationwide sample, extreme cold temperatures were associated with a greater risk of AF hospitalization. Excess risk was observed in northern China, where low temperatures prevail. This evidence highlights the importance of effective health care management and early resource allocation in high-risk regions.