It says he died in the hospital in that link, So if he died of a heart attack in the car how did he die in the hospital? The other reports I have read have none confirming he died from a heart attack or from the tree.
He had a heart attack while driving, hit the tree and died at the hospital. I think it's fair to say if he didn't have the HA he wouldn't have hit the tree so on so forth..... Does it REALLY matter?