It killed a kid in my sports class growing up as well. Dropped like a stone, cardiac arrest, couldn't be resuscitated. After that they had a 'heart health' mobile ekg come to the school once a year for people who wanted a check up which I thought was a great idea. They actually diagnosed a few people, I think at least two others with WPW but also a more common condition where the wall of the heart thickens which can also be dangerous during exercise.
The only realistic way to get someone back from ventricular fibrillation is cardioversion.
That's why automatic external defibrillators are in so many public spaces these days. If someone drops in your presence, you find that thing and get the pads on them ASAP. It won't shock if not indicated; it will tell you to resume CPR.
A former high school classmate of mine, who had played football with me from fifth grade on, dropped dead walking around in a bookstore at age 23. Almost certainly WPW.
Happened to a 38 year old bike racer in the Seattle area years ago (https://recycledcyclesracing.wordpress.com/2009/04/13/brad-l...). I didn't mention him above because it was "cardiac arrest", though I always suspected it was undiagnosed WPW. We're not talking some out-of-shape person thinking they'll run a marathon on no training. No, bike racing is unbelievably hard if you don't want to get dropped and pulled from the race after ten minutes. And Brad was good at it.
So an in-shape athlete in a hard sport at the age of 38 just drops dead mid-race from cardiac arrest? Yeah, I have theories (which, not being a cardiologist, are probably wrong).