Marathon running pace immediately before sudden cardiac arrest.

Background: Sudden cardiac arrest (SCA) is a rare but catastrophic event that can occur during long-distance road races. Although habitual training mitigates SCA risk, it remains uncertain whether running pace on race day can help identify susceptible individuals. Methods: We prospectively collected cases of SCA in Japan Association of Athletics Federations (JAAF)-certified full marathons between April 2011 and March 2020. Collapses during or within 1 hour after races that required basic life support were included. Running pace was calculated from the last available split or finish time, and expected completion times were compared with age- and sex-stratified marathon ranking data. Predicted finish time percentiles were evaluated within subgroups defined by calendar year, sex, age group, and location of collapse (race tertile or postfinish). Results: Among 4.53 million starters in 571 marathons, 74 SCA cases were identified (1.6/100,000). The median age was 52 years, and 93% were men. Over half of the events occurred in the final tertile or immediately postfinish. The median pace was 10 minutes 25 seconds per mile (interquartile range: 9:15-12:13), with an extrapolated finish time of 4 hours 33 minutes, corresponding to the 48th percentile in population rankings. Females and those collapsing in the latter part of the race tended to occupy higher percentile ranks than the general finisher distribution. Conclusions: Marathon-related SCA occurred at running speeds indistinguishable from the general finisher population, challenging the assumption that less conditioned runners are particularly at risk of SCA.