Study on the optimal definition of heatwave in subtropical regions based on cardiovascular disease mortality effects

Objective To explore the definition of heatwave in subtropical regions, and to systematically evaluate the effects of heatwave on the mortality of cardiovascular disease (CVD) and its subcategories in Fujian Province, China.

Methods Based on 66 854 CVD deaths during 2007—2015 from 9 cities in Fujian Province, a quasi-Poisson regression combined with distributed lag non-linear model was fitted to estimate the effects of heatwaves on daily CVD mortality in each city. Then the effects of heatwave on the CVD mortality of all the 9 cities were pooled using a multivariate meta-analysis to obtain the integrated effect. Stratified analyses were performed by CVD subcategory, sex, age, marital status, and educational level.

Results Heatwave was defined as daily mean temperature ≥P₉₅ with a duration of ≥4 days, which fitted well with the cardiovascular disease mortality model. The heatwave effect was acute, with a relative risk of 1.06 (95% confidence interval CI: 1.01-1.12) on the lag 0 day, 1.04 (95% CI: 1.00-1.07) on the lag 1 day, and a cumulative relative risk of 1.10 (95% CI: 1.05-1.16) on the lag 0-1 days. Heatwave also increased mortality from ischemic heart disease, chronic ischemic heart disease, and cerebrovascular disease, with relative risks of 1.13 (95% CI: 1.04-1.23), 1.24 (95% CI: 1.08-1.43), and 1.09 (95% CI: 1.02-1.16) on the lag 0-1 days, respectively. In addition, population aged 65 and over were more vulnerable to heatwave effects.

Conclusion This study suggests that the best definition of heatwave was daily mean temperature ≥P₉₅ with a duration of ≥4 days in Fujian Province, China. Under this definition, the heatwave increased mortality of CVD, ischemic heart disease, chronic ischemic heart disease, and cerebrovascular disease. In addition, population aged 65 and over were more vulnerable group to heatwave effects on cardiovascular disease mortality.