Key Points:
- This study presents updated national data from the Race Associated Cardiac Event Registry (RACER) on cardiac arrest incidence and outcomes during long-distance running races in the United States between 2010 and 2023.
- Among over 29 million race finishers, cardiac arrest occurred at a rate of 0.60 per 100,000 finishers, with significantly higher rates in men (1.12 per 100,000) compared to women (0.19 per 100,000) and marathon participants (1.04 per 100,000) versus half-marathoners (0.47 per 100,000). The overall survival to hospital discharge improved to 66% during this period, a marked increase from earlier data.
- Although cardiac arrest during long-distance running races remains exceedingly rare, enhanced emergency preparedness—particularly rapid CPR and defibrillation—has significantly improved outcomes.
Long-distance running events such as marathons and half-marathons continue to attract millions of participants annually with approximately 3 times as many finishers as compared to prior decades. Despite their association with cardiovascular fitness, these races carry a small but important risk of sudden cardiac arrest. The RACER 2 study, led by Dr. Jonathan H. Kim and colleagues and presented at the 2025 ACC Scientific Sessions and simultaneously published in JACC, sought to evaluate whether survival and incidence trends have changed with growing awareness and enhanced medical preparedness.
The database was created using publicly available information, direct contact with race directors, and USA Track and Field cardiac arrest claims. Drawing from 29.3 million race finishers and 443 U.S. marathon and half-marathon races, the study identified 176 cardiac arrests between 2010 and 2023. The majority of arrests were male (87%), with a median age of 47 years amongst survivors and 31 years amongst decedents. Notably, survival to hospital discharge was achieved in 66% of cases, a significant improvement compared to the 29% survival reported in the 2000–2009 RACER 1 analysis. Amongst the 36 cardiac arrests with full clinical profiled, bystander CPR was performed in 100% of cases, and AEDs were available and used in nearly all instances. Among survivors, 84% had an initial rhythm of ventricular tachycardia or fibrillation, while non-survivors were more likely to present with pulseless electrical activity or asystole (59%).
The etiology of the arrest was confirmed in 62 (53%) of cases. Coronary artery disease emerged as the leading cause of cardiac arrest, replacing hypertrophic cardiomyopathy as the most frequent diagnosis from the prior decade. Molecular autopsies in several decedents revealed variants of uncertain significance, while stimulant use was detected in a small subset (n=4).
Limitations of the study include different methodologies for case identification as compared to RACER 1, potential underreporting, race finishes as a surrogate for participants with the potential for selection bias and double counting, and incomplete clinical profiles in a low number of cases.
Lead author Dr. Jonathan Kim concluded in the simultaneous publication in JAMA that “the incidence of cardiac arrests during long-distance running races has been relatively stable over the last 2 decades. However, the risk of cardiac death has markedly declined since 2010. This findings suggests that concerted efforts to improve emergency action planning have led to significant improvements in outcomes.”
