Heat exposure after the rainy season is associated with an increased risk of cardiovascular emergency

Type of funding sources: None.

Climate change and global warming are some of the biggest issues in our society. Despite the growing concern for heat waves, while some previous studies have examined the effects of heat on CVD by focusing on maximum or mean daily temperature or long heat exposure periods, few studies have investigated the hourly effects of heat exposure and the risk of cardiovascular diseases (CVDs) in the elderly.

We aimed to examine the association between heat exposure and the risk of CVD in the elderly and to evaluate possible effect-measure modifications by the rainy season in East Asia.

Our study was designed as a time-stratified case-crossover. The study included 6527 residents in Japan, aged 65 years or older who were dispatched to emergency hospitals between 2012 and 2019 for the onset of CVD during and a few months after the rainy seasons. We examined the association between temperature and CVD onset for each year and for hourly intervals (lag) before the emergency call during the most relevant months.

Heat exposure during one month after the rainy season was associated with CVD risk; the odds ratio (OR) for a 1°C increase in temperature was 1.34 (95% confidence interval [CI]: 1.29–1.39). By hourly time interval (lag) before the emergency call during the month after the end of the rainy season, 0-6 hour before the case event (lag 0–6) were associated with CVD risk, particularly for lag 0–1 (OR: 1.33, 95% CI: 1.28–1.39). For longer periods, the highest risk was at lag 0-23 (OR: 1.40, 95% CI: 1.34-1.46) (Picture).

The present study suggests that heat exposure increases the risk of CVD onset during the month after the end of the rainy season in the elderly. Hourly exposure in less than one day to heat rise obtained from the temporal resolution may triggers CVD onset.