Intraday ultrashort-term effects of heat on the incidence of out-of-hospital cardiac arrest in Hangzhou, China.
Ecotoxicology and environmental safety · 2025-10-27 · Observational study
Abstract
BACKGROUND: Previous studies have shown a short-term association between heat and out-of-hospital cardiac arrest (OHCA), with the effect value being maximum on the first day. OHCA develops rapidly, so that the effects might exist after hours of exposure. However, the ultrashort-term association between them is currently unclear. METHODS: Data on OHCA in Hangzhou from 2016 to 2019 were obtained from the Hangzhou Emergency Medical Services system database. Heat was defined as the 95th percentile of the temperature distribution. This study used a time-stratified case-crossover design with conditional quasi-Poisson regression to explore the hourly associations between exposure to daytime heat and nighttime heat and OHCA incidence, and stratified analyses by age and gender to explore characteristics of relevant vulnerable populations. RESULTS: This study included a total of 1463 OHCA cases during the summer months (May - September) of 2016-2019. Heat was associated with an increased odds ratio (OR) of OHCA both during the daytime (1.872, 95 % CI: 1.282-2.733) and the nighttime (2.014, 95 % CI: 1.193-3.398). Daytime heat was associated with an increased OR of OHCA for different genders (male 2.063, 95 % CI: 1.389-3.062; female 1.569, 95 % CI: 1.043-2.360) and age groups (<65 years old 2.277, 95 % CI: 1.498-3.462; ≥65 years old 1.646, 95 % CI: 1.118-2.424); nighttime heat increased the OR of OHCA in males (1.905, 95 % CI: 1.011-3.590), females (2.431, 95 % CI: 1.089-5.430) and those ≥ 65 years old (2.923, 95 % CI: 1.499-5.701). CONCLUSION: Overall, this is the first study to explore the intraday ultrashort-term association between heat and OHCA, revealing that hourly exposure to heat is associated with an increased risk of OHCA, daytime heat increases the risk of OHCA in the whole population, and nighttime heat is associated with an increased risk of OHCA in males, females, and elderly people.