My Father Has A Pacemaker/defibulator. He Has Been In Poor

My father has a pacemaker/defibulator. He has been in poor health and pain for a few years now. When they put it in he was in 4th stage congestive heart failure. He is now 87 years old and has been hospitalized. His defibulator is going off and has been told he has indeed had a heart episode. That is all we know right now and it has been over 24 hours since he's been at the hospital. He is not hooked up to the cardio machine but he says he keeps feeling shocks. What do you think is going on here? How does someone at this stage eventually pass away? This is just frightening him over and over again. Very hard to watch?