I think I can add a little first hand insight here, as I'm one of the people who *was* in the group for young athletes suddenly dropping dead. You're going to see slightly higher incidents of electrical etiology in cardiac events in that age range (15-35). Why? We're the ones getting our heart rates way up there, Joe the Jogger and Cory the Couch Potato probably don't break a heart rate of 160 bpm unless they are straining to take a dump.
So here is my example (29 years old): Last year while on a training run, at night, solo, without a cell phone (doh). I was doing a high tempo run with my heart rate around 200 bpm; about a mile in my chest got extremely tight, I got light headed, pin point vision, sky high heart rate (estimated at 280 bpm), couldn't catch my breath, etc. etc.
I dropped to the ground and laid there dripping sweat forcing myself to take deep breathes. Since I'm not the smartest guy around, I decided to crawl/walk home back the 1 mile. It took about 40 mins to get home, during that time my extremities started to tingle and go cold.
Long story short I knew I was in cardiac shock by the time I got home, nothing was bringing my heart rate down. So got to the phone called 911, firefighters came first and got my EKG started; 268 BPM and Supraventricular tachycardia (SVT). Paramedic came (a cute one at that) and got to me the ER. My SVT broke just in time to avoid being cardioverted. Heart rate had dropped to 180 by then.
Luckily I got seen by a good ER doc, and an excellent cardiologist. Once they ruled out drugs of course. Fast forward to the diagnoses and surgery. I had Atrioventricular Nodal Reentrant Tachycardia (AVRNT) caused by extra nervous tissue (Purkinje fibers) in my left ventricle which had to be removed surgically. It was the worst case the Cardiologist had seen.
Now in my case it never showed up on an EKG and was only triggered in a very small heart rate range, during surgery it took some drugs and a lot of prodding to get it to trigger on the table. So if I didn't workout as hard it most likely would never have been an issue.
There are other conditions that can be fatal (AVRNT is rarely fatal) to athletes that most people won't be as "at risk" for because they don't push their bodies that hard.
"Go For Broke"
Fat Kine-230/24% @ 6'2"