Association between ambient temperature and out-of-hospital cardiac arrest: a systematic review and meta-analysis

BACKGROUND: Out-of-hospital cardiac arrest (OHCA) is a leading cause of cardiovascular mortality worldwide. Although ambient temperature extremes have been linked to adverse cardiovascular outcomes, evidence regarding their association with OHCA remains inconsistent. We conducted a systematic review and meta-analysis to quantify the short-term effects of ambient temperature on OHCA risk. METHODS: We systematically searched PubMed, Web of Science, and Embase from inception to September 30, 2025. for observational studies examining the association between ambient temperature and OHCA. Random- or fixed-effects meta-analyses were performed to pool relative risks (RRs) and 95% confidence intervals (CIs) for high- and low-temperature exposures. Subgroup analyses were conducted by temperature thresholds, sex, and age. Heterogeneity, publication bias, and sensitivity were assessed. RESULTS: A total of 23 studies conducted across Asia, North America, and Europe were included. High-temperature exposure was significantly associated with an increased risk of OHCA (RR = 1.067; 95% CI: 1.051-1.082), while low-temperature exposure showed a stronger association (RR = 1.192; 95% CI: 1.160-1.226). Substantial heterogeneity was observed for both high (I² = 91%) and low temperatures (I² = 96%), but sensitivity analyses confirmed the robustness of the pooled estimates. No statistically significant differences were identified across sex or age subgroups. Elevated risks were consistently observed across different percentile-based temperature thresholds, with the strongest associations noted at the 95th percentile for high temperature and across all examined low-temperature thresholds. CONCLUSIONS: Both extreme heat and cold are associated with an increased short-term risk of OHCA, with low temperature exerting a more pronounced effect. These findings highlight the importance of considering non-optimal ambient temperatures in OHCA prevention strategies and support the development of locally adaptive temperature-based early warning systems in the context of climate change.