Examining County Level Data for Extreme Heat and Cardiovascular Mortality Association

Prior studies have suggested an association between extreme heat events—temperatures significantly hotter than typical for an area—and cardiovascular mortality; however, “whether this association is present across the US or in different gender or race/ethnicity subgroups is unclear,” posited Sameed Ahmed Khatana in his study, featured at the American College of Cardiology 71st Scientific Session & Expo. Based on an analysis of daily maximum heat index and monthly cardiovascular mortality rates, Khatana judged that “a greater number of extreme heat days in a county was associated with significantly higher cardiovascular mortality rates in the US between 2008 and 2017.”

Data on maximum heat index levels for all counties in the contiguous US were retrieved from the National Environmental Public Health Tracking Network, while monthly cardiovascular mortality rates in adults aged 20 years or order were retrieved from the National Center for Health Statistics. Extreme heat days were identified, and a two-way model was constructed with the primary interest in number of extreme heat days. Other factors of the model included precipitation, drought, extreme weather events, and unemployment.

According to the report, among 3,108 counties, each additional extreme heat day during summertime months was associated with a 0.13% increase in monthly adult cardiovascular mortality rates (95% confidence interval [CI], 0.04–0.21; p = 0.005). This association was statistically significant in males (0.21%; 95% CI, 0.08–0.33), but not in females (0.03%; 95% CI, –0.0 to 0.13). Similarly, the heat-mortality association was significant for non-Hispanic Black adults (0.27%; 95% CI, 0.10–0.45), but not for non-Hispanic White (0.10%; 95% CI, –0.03 to 0.20) or Hispanic (–0.04%; 95% CI, –0.43 to 0.36) adults.

Ultimately, Khatana supported the association between extreme heat events and increased cardiovascular mortality, and further theorized that, “as extreme heat events increase, this may exacerbate pre-existing disparities in cardiovascular mortality, notably between non-Hispanic Black adults and other populations.”