March 31, 2025
4 min read
Key takeaways:
- 29 million people completed marathons or half-marathons in the U.S. from 2010 to 2023.
- Coronary artery disease was the most common etiology of sudden cardiac arrest among race runners.
CHICAGO — Good news for long-distance runners: The incidence of sudden cardiac arrest during marathons and half-marathons remained relatively stable over the past 2 decades, while the risk for sudden cardiac death markedly declined.
New data from the Race Associated Cardiac Event Registry (RACER) on more than 29 million participants of marathons and half-marathons in the U.S. were presented at the American College of Cardiology Scientific Session and simultaneously published in JAMA.
29 million people completed marathons or half-marathons in the U.S. from 2010 to 2023. Image: Adobe Stock
“Between 2010 and 2023, the incidence of sudden cardiac arrest during long-distance races has remained relatively stable — though we do appreciate an unknown, significant rise slightly since 2020 — but despite that, the risk of death has markedly declined by close to 50%,” Jonathan H. Kim, MD, MSc, associate professor of medicine, founding director of Emory Sports Cardiology and chair of the ACC Sports and Exercise Cardiology Council, said during the Featured Clinical Research presentation. “We believe this is due to continued enhancements in the emergency action plan focused on immediate [automated external defibrillator] access, deployment and placement on the racecourse and early defibrillation.”
Participation up, changes over time
For the RACER 2 trial, Kim and colleagues evaluated the incidence and outcomes of sudden cardiac arrest during U.S. long-distance running races from 2010 to 2023. Their goal was to look at changes compared with RACER 1, which looked at incidence and outcomes from 2000 to 2009, to see if changes in emergency action plan protocols made an impact over time.
The popularity of long-distance running races continues to grow. Participation in marathons and half-marathons increased threefold over the past 2 decades. More than 29 million people completed marathons and half-marathons from 2010 to 2023 compared with about 11 million people in 2000 to 2009, according to Kim and colleagues.
Among the 29 million race finishers, there were 176 sudden cardiac arrest events; 127 occurred in men, 19 in women and sex was unknown for 30 cases.
The incidence of sudden cardiac arrest was relatively unchanged over 2 decades, according to the researchers. The incidence rate was 0.54 per 100,000 participants in 2000-2009 compared with 0.6 per 100,000 participants in 2010-2023.
The rate of sudden cardiac arrest increased slightly since 2020, according to the researchers. However, the reasons for this increase after 2020 are currently unknown, they wrote in JAMA.
Jonathan H. Kim
“The sudden cardiac arrest incidence was actually relatively unchanged compared to RACER 1, but the key finding of our analysis [was] a dramatic, almost 50% reduction in terms of the incidence of sudden death,” Kim said during the presentation.
Of the 176 sudden cardiac events that occurred from 2010-2023, there were 59 deaths (34%). Of the 59 sudden cardiac events that occurred from 2000-2009, there were 42 deaths (71%). The incidence rate of sudden cardiac death declined from 0.39 per 100,000 participants in 2000-2009 to 0.2 per 100,000 participants in 2010-2023, according to the results.
Sudden cardiac arrest during races was more common among men compared with women (1.12 per 100,000 vs. 0.19 per 100,000) and also more likely to occur during marathons compared with half-marathons (1.04 per 100,000 vs. 0.47 per 100,000).
When the researchers looked specifically at men marathon runners, the incidence of sudden cardiac arrest increased from 2020-2023 (2.79 per 100,000) compared with 2010-2019 (1.43 per 100,000) and also 2005-2009 (2.03 per 100,000).
Kim and colleagues then looked at 128 identified individuals with available information (n = 77 survivors; n = 51 decedents). Survivors of sudden cardiac arrest were older (47.6 years vs. 34.4 years; P < .001); the researchers found no other differences between survivors and decedents by sex or distance of race.
A definitive cause of sudden cardiac arrest could be determined in 67 cases. In recent years, CAD was the most common etiology, in 40%, followed by “unexplained cause.” Hypertrophic cardiomyopathy was the cause in only 7%. This is different from RACER 1, in which HCM was the most common etiology, according to the researchers.
“Hypertrophic cardiomyopathy was no longer even close to the most common cause” of death, Kim said.
‘Near universal use’ of AEDs, bystander CPR
In other results, among 36 cases in which comprehensive etiologies were available, bystander CPR was performed for all.
“Among runners analyzed in [RACER 1] from 2000-2009, 58% and 48% of individuals experiencing cardiac arrest received bystander CPR and on-scene AED use, respectively. In contrast, between 2010-2023 … immediate bystander CPR was provided to all, and there was near universal use of AEDs,” Kim and colleagues wrote in JAMA.
Since the results of RACER 1 were released, there have been advancements in cardiac case ascertainment, changes in demographics of race participants, use of molecular autopsies, and more widespread availability of AEDs and bystander CPR, according to the researchers.
“The primary key finding [of RACER 2]: It wasn’t just reduced CPR time that predicted survival; it was the presence of a shockable rhythm,” Kim said during the presentation.
For RACER 2, the researchers utilized a record of race finishers, comprehensive review of cases from media reports, direct contact with race directors, USA Track & Field claims, medical records or autopsy reports, and interviews with survivors or next of kin. The researchers noted several limitations of the current study, including differences in case ascertainment between RACER 1 and 2 and etiologies available for only approximately 50% of cases, leading to incomplete clinical profiles.
“When we think about the highest-risk demographic — men who run marathons — each year, if you combine the Chicago Marathon and New York City Marathon, that’s one man who is going to suffer a sudden cardiac arrest. And that hasn’t changed over 23 years. These are incidence statistics that really I think we can improve on. So, as we look to the future, I think that is our focus: opportunities for primary prevention strategies for the masters endurance athlete [and] certainly some of these higher-risk demographics,” Kim said during the presentation.
Reference:
Sources/Disclosures
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Kim JH, et al. Featured clinical research I. Presented at: American College of Cardiology Scientific Session; March 29-31, 2025; Chicago (hybrid meeting).
Disclosures:
Kim reports receiving grant funding from the Atlanta Track Club and the NIH. Please see the study for all other authors’ relevant financial disclosures.