“One in every 100 cardiovascular deaths may be attributed to extreme temperature days,” and “only 20% of patients with heart failure survive 10 years after diagnosis.”

New research published today in Circulation, the flagship journal of the American Heart Association, found that both extremely hot and cold temperatures increased the risk of death among people with cardiovascular diseases like ischemic heart disease (heart problems caused by narrowed heart arteries), stroke, heart failure, and arrhythmia.

This research found that heart failure caused the most excess mortality from very hot and cold conditions among cardiovascular disorders.

“The decline in cardiovascular death rates since the 1960s is a huge public health success story as cardiologists identified and addressed individual risk factors such as tobacco, physical inactivity, Type 2 diabetes, high blood pressure and others. The current challenge now is the environment and what climate change might hold for us,” remarks Barrak Alahmad.

Researchers looked at how high temperatures might affect heart diseases, which are the leading cause of death around the world. They looked at health data for more than 32 million people who died of heart disease or stroke between 1979 and 2019. These deaths happened in 567 cities in 27 countries on 5 continents. The global data came from the Multi-Country Multi-City (MCC) Collaborative Research Network, which is a group of epidemiologists, biostatisticians, and climate scientists studying how climate and other environmental stressors affect health and death rates.

Since climate change is linked to large shifts in both hot and cold extremes, this study analyzed both. For this study, researchers looked at cardiovascular deaths on the hottest and coldest 2.5% of days in each city and compared them to cardiovascular deaths on the days with the optimal temperature, which is the temperature that is linked to the fewest deaths in that city.

They discovered that for every 1,000 deaths from cardiovascular disease:

• Extremely hot days caused an extra 2.2 deaths.
• Extreme chilly days killed 9.1.
• People with heart failure were found to die more often than people with other types of heart disease (2.6 additional deaths on extreme hot days and 12.8 on extreme cold days).

According to Haitham Khraishah, M.D., a cardiovascular disease fellow at the University of Maryland School of Medicine and the University of Maryland Medical Center in Baltimore and a co-author of the study, “One in every 100 cardiovascular deaths may be attributed to extreme temperature days, and temperature effects were more pronounced when looking at heart failure deaths.” 

Although the cause is unknown, it may be related to the fact that heart failure is a progressive condition that makes patients more vulnerable to temperature effects. This is an important finding because one in four people with heart failure are readmitted to the hospital within 30 days of being discharged, and only 20% of people with heart failure live 10 years after being diagnosed.

Researchers believe that in order to avoid cardiovascular fatalities during temperature extremes, specific warning systems and counselling for susceptible populations may be required.

“We need to be on top of emerging environmental exposures. I call upon the professional cardiology organizations to commission guidelines and scientific statements on the intersection of extreme temperatures and cardiovascular health. In such statements, we may provide more direction to health care professionals, as well as identify clinical data gaps and future priorities for research,” Alahmad adds.

The lack of data from South Asia, the Middle East, and Africa makes it difficult to extrapolate these results to create worldwide estimates of the influence of severe temperatures on cardiovascular fatalities.

This work adds significant knowledge to the current social debates on the connection between climate change and human health. 

“More work is needed to better define these relationships in a world facing climate changes across the globe in the years ahead, especially as to how those environmental changes might impact the world’s leading cause of death and disability, heart disease,” adds AHA Past President Robert A. Harrington.

Source: 10.1161/CIRCULATIONAHA.122.061832

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