Extreme temperatures and out-of-hospital cardiac arrest: a systematic review and narrative synthesis

To systematically assess the association between exposure to extreme ambient temperatures and the incidence and outcomes of out-of-hospital cardiac arrest (OHCA).

A systematic review was conducted in accordance with PRISMA 2020 guidelines. Medline, PubMed, Embase, Scopus, and Web of Science were searched from inception for observational studies examining the relationship between temperature extremes and OHCA incidence and outcomes. Two reviewers independently screened studies, extracted data, and assessed risk of bias using the ROBINS-E tool. The review was registered prospectively with PROSPERO (CRD42024604822).

Thirty-one studies across Asia, Europe, North America, the Middle East, and Oceania were included. Most used time-series or case-crossover designs drawing on Emergency Medical Services (EMS) or cardiac arrest registry data. A U- or J-shaped exposure-response relationship was observed across most settings, with elevated OHCA incidence at both cold and hot temperature extremes, although effect magnitudes, thresholds, and lag structures varied substantially. Cold exposure accounted for a substantially greater proportion of temperature-attributable OHCAs compared with heat. Temperature extremes were also associated with poorer clinical outcomes, including lower rates of return of spontaneous circulation, reduced survival to hospital discharge, and worse neurological outcomes, particularly in periods of cold exposure.

Extreme ambient temperatures represent significant, climate-sensitive and potentially modifiable determinants of OHCA incidence and outcomes. As climate change intensifies temperature variability and prolongs both heat and cold extremes, integrating environmental data into OHCA surveillance, risk forecasting, prevention strategies, and EMS planning becomes increasingly urgent.