Passive Heat Exposure Linked to Increased Heart Stress, Study Reveals

A controlled laboratory experiment involving both healthy adults and adults with coronary artery disease (CAD) found that passive heat exposure significantly increased myocardial blood flow (MBF) in all participants, regardless of age and health status, thereby placing considerable stress on the heart.

The study was published in the journal Annals of Internal Medicine.

Coronary artery disease is a leading cause of mortality worldwide, characterized by the narrowing or blockage of coronary arteries due to plaque buildup. This condition restricts blood flow to the heart, increasing the risk of heart attacks. CAD affects millions globally, with rising prevalence due to factors like poor diet, lack of exercise, and smoking.

Recent studies have shown that passive heat exposure, such as from hot environments or certain medical treatments, can significantly increase myocardial blood flow (MBF). Heat exposure can cause significant stress on the heart leading to a supply-demand mismatch in vessels exhibiting flow-limiting disease. Repeated exposures, can result in symptomatic or silent ischemia and increase the risk for adverse cardiovascular events.

In the study, researchers from the Montreal Heart Institute conducted an experimental study comprised of 20 healthy young adults, 21 healthy older adults, and 20 older adults with CAD to quantify the MBF requirements of heat exposure. In a laboratory setting, participants were heated until their core temperature increased 1.5 degrees Celsius (C), and their MBF was measured before exposure and at every increase of 0.5 degrees C to their core temperature.

The result showed that myocardial blood flow increased in all participants when their body temperature increased by 1.5 degrees C. Researchers additionally observed that 7 participants with coronary artery disease experienced asymptomatic heat-induced myocardial ischemia based on imaging evidence.

The findings revealed that heat exposure that increases core temperature by 1.5 °C nearly doubles myocardial blood flow. Changes in myocardial blood flow did not differ by age or presence of coronary artery disease, but some older adults with coronary artery disease may experience asymptomatic myocardial ischemia.

Reference: Hadiatou Barry, Josep Iglesies-Grau, Georgia K. Chaseling, et al. The Effect of Heat Exposure on Myocardial Blood Flow and Cardiovascular Function. Ann Intern Med. [Epub 11 June 2024]. doi:10.7326/M24-3504