Loading ...

Despite increased participation in long-distance running races in the United States, the rate of cardiac arrests among runners remains stable, but survival has improved dramatically, according to the RACER 2 study.

Almost 30 million people who finished a marathon or half-marathon between 2010 and 2023 were identified for the study, conducted by Jonathan Kim, MD, cardiologist at Emory University in Atlanta, and his colleagues. In their RACER 1 study, the team assessed cardiac arrests in roughly 10 million people who finished a marathon from 2000 to 2009.

So with race participation almost tripling over the past two decades, changes in runner demographics, and improved emergency action plans, the team decided it was time to revisit the issue, Kim explained during his presentation of the RACER 2 results at the American College of Cardiology (ACC) Scientific Session 2025 in Chicago, which were simultaneously published in JAMA.

RACER 1 and RACER 2

In both studies, the incidence of cardiac arrest was about the same: Roughly one in 200,000 people. But the fatality rate decreased significantly between RACER 1 and RACER 2, from 71% to just 34%. In RACER 2, the risk for death in men was about one in 100,000. For women, the risk is much lower, at about one in 500,000. Risk was also higher in full marathons than in half-marathons.

Over the years, “the incidence of cardiac arrest has remained relatively stable, apart from a slight unexplained rise after 2020, but despite that, the risk for death has markedly declined, by close to 50%. We believe this is due to continued enhancements in the emergency action plans,” which are focused on immediate access to automated external defibrillators (AEDs), said Kim.

In RACER 1, bystander cardiopulmonary resuscitation was the biggest predictor of survival, but just 58% of runners received it. In RACER 2, that had risen to 100%, and race organizers were ensuring access to more AEDs. In RACER 1, the highest risk for a cardiac arrest was at the end of the race, so by the time RACER 2 was conducted, organizers had learned to strategically position more defibrillators near the finish line.

This highlights the importance of preparation and training for race organizers, said Benjamin Levine, MD, sports cardiologist at the University of Texas Southwestern Medical Center in Dallas, which is a major take-home message of the recent scientific statement on the care of competitive athletes with cardiac abnormalities, issued jointly by the ACC and the American Heart Association, which both he and Kim worked on.

“All of us in the sports cardiology world want to prevent death, but you can’t do it with screening alone,” Levine explained. “If you want to prevent deaths in sports, you’ve got to have an emergency action plan, you’ve got to have an AED, and you have to practice with it.”

Over time, there has also been a change in the causes of cardiac arrests, when they were identified. In RACER 1, the most common cause was hypertrophic cardiomyopathy, whereas in RACER 2, coronary artery disease took the top spot.

The reason for that change is unclear and should be taken with a grain of salt, given that good clinical information was not available for all of the incidents. “Nevertheless, I think the etiology has shifted in recent decades,” said Levine. And although coronary artery disease was the most common cause of death in RACER 2, it is also the cardiac arrest with the highest survival rate.

The risk is there, but incidents remain rare, and there is a lot that runners can do to reduce their own risk.

“For older runners, in particular, it’s important to pay attention to symptoms and ensure your risk factors are as much under control as possible,” Levine said. “And discuss it with your doctor if your personal risk is higher.”

Kim and Levine had no disclosures to report.