Study Predicts Alarming Increase in Cardiovascular Deaths Due to Impact of Extreme Heat

New research published this week in Circulation showed that extreme heat was associated with 1,651 excess cardiovascular deaths per year from 2008 to 2019. The study further concludes that extreme heat is projected to lead to a significantly higher burden of excess cardiovascular deaths in the United States by midcentury (2036–2065), with elderly adults and non-Hispanic Black adults being most affected.

Extreme heat poses a greater risk to individuals with heart disease and cardiovascular risk factors. The cardiovascular system plays a vital role in thermoregulation by facilitating heat exchange with the environment, regulating blood flow to the skin, enabling sweat production, and distributing thermoregulatory hormones. These actions help the body maintain a stable internal temperature.

Climate change has led to increased extreme weather events, including more frequent and hotter heat waves in the United States and around the globe. Almost half of the global population is exposed to high heat episodes, with about a third of exposed workers experiencing negative health effects. As climate change continues, extreme heat events are projected to increase.

Furthermore, the expected increase in the number of extreme heat events will coincide with anticipated demographic changes in the United States, such as an increase in migration to hotter areas as well as an aging population. It is uncertain how the projected increase in extreme heat and changes in demographics will affect the burden of heat-related cardiovascular deaths.

To address this uncertainty, an investigation was conducted by a group of researchers led by Sameed Khatana, M.D., M.P.H., cardiologist and assistant professor of medicine at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia.

To investigate, the researchers collected data on cardiovascular deaths and extreme heat days in the United States from 2008 to 2019. Extreme heat days were defined as days with a maximum heat index ≥90°F (32.2°C). Next, they used models to predict future greenhouse gas emissions and different socioeconomic scenarios. Specifically, two scenarios were considered: SSP2-4.5, which represents a “middle-of-the-road” socioeconomic scenario with moderate emissions, and SSP5-8.5, which represents an economy heavily reliant on fossil fuels with high emissions. Using various statistical models, they calculated the projected number of excess cardiovascular deaths associated with extreme heat.

The results revealed that from 2008 to 2019, extreme heat was associated with 1,651 excess cardiovascular deaths per year. This means that during this period, extreme heat occurrences were linked to an additional 1,651 deaths annually compared to what would be expected under normal temperatures. By midcentury (2036–2065), under the SSP2-4.5 scenario (moderate emissions), the projected annual excess deaths associated with extreme heat is estimated to be 4,320—an increase of 162%. Under the SSP5-8.5 scenario (high emissions), the projected annual excess deaths associated with extreme heat is estimated at 5,491, representing an increase of 233%.

In addition, in the SSP2-4.5 scenario, the results found that elderly adults are projected to have a 3.5 times greater increase in deaths compared to nonelderly adults. Non-Hispanic Black adults are projected to have a 4.6 times greater increase compared to non-Hispanic White adults. There were no significant differences in projected deaths between other race and ethnicity groups or between men and women.

“This study builds on our previous work, which demonstrated that extreme heat is associated with higher cardiovascular mortality rates in the United States. This paper shows that not only are extreme heat-related cardiovascular deaths expected to increase substantially in the coming decades, but that the burden will be felt disproportionately by some groups, notably older individuals and non-Hispanic Black adults,” Khatana said in an email interview with Managed Healthcare Executive.

Regarding the implications of this research for people living with heart failure, Khatana said: “Although our study did not examine specific types of cardiovascular deaths, previous studies have shown that extreme heat is related to higher levels of deaths from ischemic heart disease, stroke, and heart failure.” He further explained that individuals with heart failure “may be particularly vulnerable to the adverse health effects of extreme heat, given their poor cardiac reserve and use of medication such as beta-blockers and diuretics that can increase health risks.”

“Urgent public health and infrastructure interventions are needed to help communities adapt to the projected increases in extreme heat and to mitigate its adverse health effects,” the authors wrote.

FYI I took this last quote from the Clinical Implications box from the full text version of the study. The other quotes above are from an email from Dr. Khatana.