Extreme Heat Seems to Spark More Atrial Arrhythmias in IED Patients

When the temperature outside rises, particularly above 100°F, it appears the risk of atrial arrhythmias among patients with cardiac implantable electronic devices also goes up, new data show.

The likelihood of atrial fibrillation (AF) or atrial tachycardia (AT) was significantly higher starting at temperatures around 86°F, when compared with a reference of 66°F. Odds ratios rose to 2.24 or higher when temperatures exceeded 100°F, according to a study Barrak Alahmad, MD, PhD (Harvard T.H. Chan School of Public Health, Boston, MA), presented yesterday as a digital poster at American Heart Association (AHA) 2024 Scientific Sessions.

For ventricular arrhythmias, there was no such connection with hot temperatures but there was a “suggestive but not conclusive association with extreme cold,” Alahmad told TCTMD.

These findings are not definitive, he said, though this study is believed to be the largest investigation into the possible link between environmental exposures and arrhythmias, covering more than 100 US cities with a wide temperature range.

Alahmad said that in the absence of concrete guidance from professional societies regarding the relationship between temperature and arrhythmia risk, “the least we could do with findings like these is to activate the precautionary rule, which is just take extra caution right now while we investigate what should be done and how can clinicians intervene to prevent these events from happening when the temperatures are increasing.”

Not only is the problem not going away, but also it will likely get worse as global temperatures rise due to climate change, he stressed. Although there are numerous well-established risk factors for atrial arrhythmias, like smoking and alcohol use, extreme temperatures could be an emerging risk factor, he added. Researchers will need to “pick up the pace” to better understand the underlying mechanisms and which clinical interventions are effective, said Alahmad.

Risks of Hot Weather

Prior studies have shown that high temperatures can adversely impact cardiovascular health, with one suggesting that intense heat was associated with an excess of cardiovascular death. Last year, Alahmad’s group reported that CVD deaths were increased at both high and low temperature extremes.

To dig into why that might be, the investigators decided to examine the impact of temperature on risk of atrial arrhythmias. They used data from Medtronic’s Product Surveillance Registry on 3,079 patients (mean age 70.6 years; 78% men) living in 103 US cities who received an implantable cardioverter-defibrillator or cardiac resynchronization therapy-defibrillator between January 2016 and April 2023.

For the patients, atrial arrhythmia episodes detected by their devices were matched with ambient temperature recordings from the meteorological station nearest to where they underwent implantation.

Compared with a reference temperature of 66°F, the odds of AF/AT were significantly higher starting at 86.0°F (OR 1.33; 95% CI 1.18-1.50), with stronger relationships observed at higher temperatures:

• 102.2°F (OR 2.41; 95% CI 1.37-4.25)
• 104°F (OR 2.60; 95% CI 1.38-4.89)
• 105.8°F (OR 2.81; 95% CI 1.40-5.63)
• 107.6°F (HR 3.03; 95% CI 1.41-6.49)

An additional analysis confined to arrhythmia episodes lasting 30 seconds or longer provided similar results.

Alahmad provided some potential explanations for the findings, noting that as the outside temperature rises, so does the body’s core temperature, which in turn increases metabolic demand and heart rate. Hot weather can also lead to dehydration, volume depletion, and loss of electrolytes like magnesium and potassium. “That loss of electrolytes plus the increase in heart rate that happens at the same time could trigger” these atrial arrhythmias, he said.

In commentary prepared for the media by the AHA, Sanjay Rajagopalan, MD (University Hospitals Harrington Heart & Vascular Institute, Cleveland, OH), noted that additional studies will be needed to replicate these findings in larger groups of people, including those without implanted devices and those from more vulnerable communities.

Still, the results are not very surprising, said Rajagopalan, chair of a 2024 AHA policy statement on moving toward heart-healthy and sustainable cities, because “there’s an increasing body of evidence linking temperatures with a variety of adverse cardiovascular events.”

It’s not, therefore, “premature to provide guidance to vulnerable populations to avoid these types of days,” he said, suggesting that people can seek shelter in air-conditioned environments when outside temperatures are high. “Communities and neighborhoods and cities and obviously counties could be very much more oriented towards providing these types of accommodations for individuals.”