Abstract Sat1305: During endurance races: half of sudden cardiac arrest cases remain unexplained.

Background: Sport-related Sudden Cardiac Arrest (Sr-SCA) can occur even apparently healthy athletes. Cardiomyopathies and channelopathies have consistently been implicated as leading causes of SCA in young competitive athletes. However, these findings may not fully apply to long-distance runners, who tend to be older and present with different cardiovascular risk factors and pre-existing conditions leading to ischemic diseases. Method: We merged two prospectively collected databases. The first source was a regional registry that recorded 55000 out-of-hospital cardiac arrests in adults (October 2011 – April 2024). The second source contained official participation lists for 20 km race, half-marathon (HM) and full marathon (FM) for the same period (all years except 2020). Only finishers and Sr-SCA events were analyzed. Comprehensive in-hospital work-up included ECG, echocardiography, coronary angiography, cardiac MRI and drug-provocation tests; when indicated, electrophysiological study, Holter monitoring, signal-averaged ECG, endomyocardial biopsy and genetic testing were added. Results: Over the past 10 years, among 1.2 million participants (mean age 38 ± 11 years, 71.6% men), there were 17 SCA cases (7 in 20km, 5 in HM and 5 in FM). Among these cases, 88% (15/17) were men, with a mean age of 42 ± 13 years. Etiology remained undetermined in 8 cases (47.1 %) despite exhaustive evaluation (Figure 1). A cause was identified in 8 patients: ischemic cardiomyopathy (n=5), Brugada syndrome (n=1), myocarditis (n=1), and an anomalous right coronary artery (n=1). One patient carried heterozygous SCN5A and VCL variants that may explain the Sr-SCA. Ischemic cardiomyopathy accounted for 60% (3/5) of FM cases, 20% (1/5) of HM cases and 14.3% (1/7) of 20 km race cases. Conclusion: Despite extensive in-hospital medical assessments, half of the cases remained unexplained. These results contribute to the ongoing debate on pre-participation screening in sport and the proposed strategies to mitigate the occurrence of Sr-SCA.