It's sounds like anoxic brain injury, from cardiopulmonary arrest - as you say, but this wasn't from a ‘heart attack’ (occlusion of a coronary artery) in an otherwise healthy 22 year old. They either overmedicated him with something that caused him to stop breathing, or they tortured him in some way. Even water boarding, taken to the extreme, could do this if they went too long and essentially induced the equivalent of drowning. There are a ton of things they could have done to cause this, but none of them are acceptable. Did they really think he was a spy? Sick.
There's a lot we aren't being told by the Dr.s here and the family. .....the idea is to protect the family from any further distress in an already extremely difficult and unimaginable situation.
Anything can happen in N.Korea....why anyone would even consider going there is beyond my understanding......50 years of torturing and killing their own people...and taking Americans hostages for monetary gain, along with a propaganda machine that tells their people to hate Americans.... should be plenty enough to put up blaring red lights......unfortunately people will always run lights and sirens and do their own thing regardless.