Joint Effects of Heat and Fine Particulate Matter on Out-of-Hospital Cardiac Arrest in Japan: A Nationwide Time-Stratified Case-Crossover Study.
Journal of the American Heart Association · 2026-07-17 · Registry study
Abstract
BACKGROUND: Out-of-hospital cardiac arrest (OHCA) is a leading cause of cardiovascular death. Although ambient temperature and particulate matter with an aerodynamic diameter ≤2.5 μm (PM2.5) are established risk factors, evidence on their joint effects remains limited. We assessed the joint effects of heat and PM2.5 on OHCA risk using nationwide data from Japan. METHODS: We collected daily data on cardiac-origin OHCAs from the All-Japan Utstein Registry and daily temperature and PM2.5 from monitoring networks across 47 prefectures during 2012 through 2019. Using a 2-stage time-stratified case-crossover design, we estimated prefecture-specific associations with conditional quasi-Poisson models and pooled them using meta-regression. Interactions between temperature and PM2.5 were assessed on multiplicative and additive scales using the relative excess risk due to interaction. Attributable cases were also estimated. RESULTS: A total of 610 613 cardiac-origin OHCAs were included. Heat (relative risk, 1.04 [95% CI, 1.02-1.06]; 99th versus 80th percentile); and PM2.5 (relative risk, 1.02 per 10 μg/m3 [95% CI, 1.01-1.03]) were independently associated with increased OHCA risk. Heat effects were amplified at higher PM2.5 concentrations, with each 10 μg/m3 increase in PM2.5 associated with an additional 1.8% increase in heat-related risk. Conversely, PM2.5 effects increased by 1.2% (95% CI, 1.1%-1.2%) per 25th percentile increase in temperature. Interactions were observed on both scales (relative excess risk due to interaction, 0.01 [95% CI, 0.00-0.02]; P=0.003). Overall, 2638 OHCA cases were attributable to coexposure, exceeding the combined burden attributable to heat (1215) and PM2.5 (1276) separately. CONCLUSIONS: Heat and PM2.5 acted synergistically to increase OHCA risk, highlighting the need for integrated public health strategies addressing both extreme heat and air pollution under climate change.