Here's an amazing video of a soccer player in Europe. This guy obviously had a defibrillator. He went into a lethal heart rhythm (probably like Gaines Adams), and passes out -- but the defibrillator shocked this guy (see his body shake) - and he lived.
YouTube - Football player has heart attack but survives!
Atheletes are very carefully screened by doctors before playing sports.. Again, Gaines must've slipped through the cracks..