• Posted November 11, 2024

Have an Implanted Defibrillator? Triple-Digit Heatwaves Could Pose Danger

Thousands of Americans with heart trouble have small implanted defibrillators, to help regulate their heartbeat and keep cardiac events at bay. 

But new research finds that on extremely hot days, people with the devices face nearly triple the odds for a dangerous arrhythmia known as atrial fibrillation (A-fib), compared to days with cooler temperatures.

The threat is likely to rise as climate change makes triple-digit days more common, experts noted.

“Susceptible individuals living in areas at risk for markedly increased temperatures should take note of these findings and ensure that they take appropriate precautions to stay cool and hydrated,”  said Dr. Sanjay Rajagopalan, an expert working with the American Heart Association (AHA). He wasn't involved in the new study.

“This may be the first study that has linked ICD detection of A-fib with temperature spikes,” Rajagopalan, a professor at Case Western Reserve University in Cleveland, said in an AHA news release.  “These findings reiterate other recent research about the link between outdoor temperature and cardiovascular health. Given the rising prevalence of A-fib in the general population due to increasing age and the prevalence of obesity, we now may also have to contend with rising temperatures."

The new findings are scheduled be presented today at the AHA's annual meeting in Chicago.

The new study was led by Dr. Barrak Alahmad, a research fellow in environmental health at the Harvard T.H. Chan School of Public Health in Boston. His team tracked data on more than 2,000 patients nationwide who got either an implanted cardioverter-defibrillator (ICD) or cardiac resynchronization therapy defibrillator (CRT-D) device between 2016 and 2023.

Patients averaged about 70 years of age and most (78%) were men. Obesity was common, and most patients had cardiomyopathies, where the heart loses its pumping efficiency.

Implanted defibrillators record episodes of A-fib, so the team correlated those episodes with the outside temperatures reported in the patient's locale on the day the A-fib occurred.

The team noted that the "optimal" outside temperature -- most likely to reduce the odds of A-fib -- is relatively cool, at between 41 and 46 degrees Fahrenheit.

However, extremely high temperature days pushed a defib user's odds for A-fib much higher. 

For example, compared to the ideal outside temperature, participants had nearly three times of developing A-fib on a days registering 102.2 degrees F or higher, Alahmad's team reported.  

The odds for A-fib episodes on hot days were lowest in the morning but increased through working hours, and risks rose more on workdays compared to weekends.

More research revealed that these trends were also true for long A-fib episodes -- those lasting 30 minutes or longer. 

“We need to understand the physiological processes underlying these findings and concentrate on preventing conditions that trigger A-fib to minimize the burden of arrhythmias,” study co-author Dr. Theofanie Mela, a cardiac electrophysiologist at Massachusetts General Hospital in Boston, said in a AHA news release. “In the meantime, we recommend patients avoid extreme temperatures and use air conditioners so that they do not expose their bodies to the severe stress of extremely high heat.”

Because these findings were reported at a medical meeting, they should be considered preliminary until published in a peer-reviewed journal.

More information

Find out more about how defibrillators work at the National Heart, Lung and Blood Institute.

SOURCE: American Heart Association, news release, Nov. 11, 2024