i dono much details but its heart attack.
I think its because sometimes after a heart attack the lungs get affected, and organ failure occurs, so they put a person on artificial ventilation where the machine does most of the breathing. Usually if its an infection of the lungs or something, they know taking the ventilator off is fairly safe (weaning process) after the infection subsides and goes away, but if its organ damage then its always very risky. Its very sad to hear he was only in his mid forties, thats a very young age.