100⁰ F temps linked to irregular heartbeat in those with implanted defibrillators, suggests study

Exposure to temperatures of 100°F (38°C) or higher may nearly triple the number of episodes of a form of irregular heart rhythm, known as atrial fibrillation or AFib, in people with implantable cardioverter defibrillators (ICDs), according to a preliminary study to be presented at the American Heart Association’s Scientific Sessions 2024.

The meeting, Nov. 16-18, 2024, in Chicago, is a premier global exchange of the latest scientific advancements, research and evidence-based clinical practice updates in cardiovascular science.

“AFib is becoming more prevalent both in the U.S. and globally, with its incidence rising at an alarming rate,” said study lead author Barrak Alahmad, M.D., Ph.D., M.P.H., a research fellow in environmental health at the Harvard T.H. Chan School of Public Health in Boston.

It is estimated that more than 12 million people will be living with AFib by 2030, according to the American Heart Association’s 2024 Heart Disease and Stroke Statistics. Heart disease and other medical conditions increase the risk of developing atrial fibrillation; however, the role of heat-induced stress in triggering this condition remains understudied.

Researchers examined health data for more than 2,000 U.S. adults with an implanted cardioverter-defibrillator (ICD) or cardiac resynchronization therapy defibrillator (CRT-D) device implanted between 2016 and 2023 across more than 100 cities in the U.S. These electronic devices are inserted into a person’s chest to monitor and regulate the heartbeat.

For each patient, the first episode of atrial fibrillation detected on the device was matched to hourly outdoor temperature data on the day of the episode for the location of the hospital or health care center where they received their device. Researchers then categorized the AFib episodes for each study participant by the time of day and day of the week with corresponding outdoor temperatures. The aim was to determine the effect, if any, of being exposed to temperatures that exceeded 100°F (38°C) in their geographical location. The relationship between outdoor heat and episodes of atrial fibrillation was determined for the whole study population.

The study found:

Compared to optimal outdoor temperatures between 41°F and 46.4°F (5°C to 8°C ), which had the lowest odds of causing an episode of AFib, when outdoor temperatures reached 102.2°F, 104°F and 105.8°F (39°C, 40°C and 41 °C), the odds of experiencing an episode of AFib were 2.66 times higher, 2.87 times higher and 3.09 times higher, respectively.

Fewer AFib episodes occurred in the early morning hours (12 a.m. to 7 a.m.) compared to standard working hours (8 a.m. to 5 p.m.).

Episodes of AFib were more common on weekdays than weekends.

An additional analysis that evaluated episodes of AFib that lasted longer than 30 minutes found similar results.

“We need to understand the physiological processes underlying these findings and concentrate on preventing conditions that trigger AFib to minimize the burden of arrhythmias,” said study co-author Theofanie Mela, M.D., a cardiac electrophysiologist at Massachusetts General Hospital in Boston. “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.”

American Heart Association volunteer expert Sanjay Rajagopalan, M.D., M.B.A., FAHA, who chaired the Association’s 2024 policy statement on transforming key urban provisioning systems to heart-health and sustainability outcomes, noted that heat stress has been implicated in an increase in cardiovascular disorders, including stroke, heart attack and cardiovascular death. However, few studies have examined the link between atrial fibrillation and heat stress.

“This may be the first study that has linked ICD detection of AFib with temperature spikes,” said Rajagopalan, chief of cardiovascular medicine at University Hospitals Harrington Heart and Vascular Institute and a professor at Case Western Reserve University, both in Cleveland. “These findings reiterate other recent research about the link between outdoor temperature and cardiovascular health. Given the rising prevalence of AFib in the general population due to increasing age and the prevalence of obesity, we now may also have to contend with rising temperatures.

“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,” he added. “Unfortunately, the most vulnerable people may be those in lower socioeconomic groups who may not have access to air conditioning and other means of sheltering during warm days.”

Overall, this study cannot draw definitive conclusions for several reasons. Local weather stations measured temperatures where the patients received their ICDs, and this may not be the same as where patients lived. As a result, it’s impossible to be certain that study participants were exposed to the high temperatures recorded by the local weather stations.