IMPORTANCE: More than 29 million participants completed marathons and half-marathons in the US between 2010-2023, approximately 3 times the number from 2000-2009. Contemporary long-distance race-related cardiac arrest incidence and outcomes are unknown. OBJECTIVE: To determine the incidence and outcomes of cardiac arrests during US marathons and half-marathons between 2010-2023 from a record of race finishers and a comprehensive review of cases from media reports, direct contact with race directors, USA Track & Field claims, and interviews with survivors or next of kin. DESIGN, SETTING, AND PARTICIPANTS: Observational case series from the Race Associated Cardiac Event Registry
cohort data from US marathon and half-marathon runners from January 1, 2010, to December 31, 2023. Case profiles were reviewed to determine etiology and factors associated with survival. Incidence and etiology data were compared with historical reference standards (2000-2009). EXPOSURE: Recreational long-distance running (marathon and half-marathon distance). MAIN OUTCOMES: Incidence proportions of sudden cardiac arrest and death. RESULTS: Among 29 311 597 race finishers, 176 cardiac arrests (127 men, 19 women, 30 sex unknown) occurred during US long-distance running races. Compared with 2000-2009, cardiac arrest incidence remained unchanged (incidence rate, 0.54 per 100 000 participants [95% CI, 0.41-0.70] vs 0.60 per 100 000 [95% CI, 0.52-0.70], respectively). However, there were significant declines in cardiac death incidence (0.20 per 100 000 [95% CI, 0.15-0.26] vs 0.39 per 100 000 [95% CI, 0.28-0.52]) and case fatality rate (34% vs 71%). Cardiac arrests remained more common among men (1.12 per 100 000 [95% CI, 0.95-1.32]) than women (0.19 per 100 000 [95% CI, 0.13-0.27]) and during the marathon (1.04 per 100 000 [95% CI, 0.82-1.32]), compared with the half-marathon (0.47 per 100 000 [95% CI, 0.38-0.57]). Among runners for which a definitive cause of cardiac arrest could be determined (n = 67/128 [52%]), coronary artery disease rather than hypertrophic cardiomyopathy was the most common etiology. Decreased cardiopulmonary resuscitation time and an initial ventricular tachyarrhythmia rhythm were associated with survival. CONCLUSIONS AND RELEVANCE: Despite increased participation in US long distance running races, cardiac arrest incidence remains stable. There has been a marked decline in cardiac arrest mortality, and coronary artery disease was the most common etiology among cases with sufficient cause-related data. Effective emergency action planning with immediate access to defibrillation may explain the improvement in survival.