Usually if it’s a young athlete and African American descent, most typically it’s hypertrophic cardiomyopathy. Overtraining and dehydrated can also lead to severe electrolyte deficiencies can also make you prone to cardiac arrest from arrhythmia. I think last year there was a marathon runner who had cardiac arrest near the finish line in the Sacramento area.with these situations you never know if it's genetic or if its a form of overtraining, which happens quite frequently in youth sports and amateur.