Interaction of Extreme Temperature Events and Nitrogen Dioxide on Out-of-Hospital Cardiac Arrest in a Subtropical Megacity: A Time-Series Analysis.
Journal of the American Heart Association · 2026-06-23 · Observational study
Abstract
BACKGROUND: Extreme temperature events and nitrogen dioxide are established risk factors for cardiovascular disease, often co-occurring during cold spells. However, their additive interactive effects on out-of-hospital cardiac arrest (OHCA) in subtropical climates remain unclear. METHODS: Time-series analysis was performed using 16 769 OHCA cases in Shenzhen, China (2015-2019). Extreme temperature events were defined by apparent temperature: cold spells and heatwaves were stratified by percentile thresholds (2.5th-10th for cold, 90th-97.5th for heat) and consecutive durations (2-4 days). Quasi-Poisson regression with distributed lag nonlinear models was applied, and additive interactions were evaluated using relative excess risk due to interaction, attributable proportion, and synergy index. RESULTS: Cold spells were associated with a significant severity-dependent increase in OHCA risk, with risk ratios (RRs) rising from 1.19 (95% CI, 1.13-1.26) for mildest definition (≤10th percentile for ≥2 days) to 1.50 (95% CI, 1.26-1.78) for most extreme definition (≤2.5th percentile for ≥2 days), whereas heatwaves showed no significant associations. Cold spells and nitrogen dioxide (lag 0-3 days) showed significant synergy. Under the most extreme cold spell, coexposure yielded the highest risk (RR, 1.543 [95% CI, 1.307-1.822]), with 27.7% of OHCA cases attributable to this interaction. This synergy was most pronounced for shockable rhythms (relative excess risk due to interaction up to 1.57 [95% CI, 0.34-2.79]). CONCLUSIONS: Extreme cold and nitrogen dioxide synergistically increase OHCA risk in subtropical megacities, particularly for shockable rhythms-reversible with prompt defibrillation. Integrated early-warning systems targeting compound cold and pollution exposures are needed to reduce mortality.