In 1985, I was camping with my family in a large beach campground. One of us noticed a neighboring camper laying on the ground. I went over to check him and he was in full cardiac arrest. I'd learned CPR in the service, and I started working on him. Since we were at a beach, we had lifeguards arrive in about two minutes and they took over. They hooked up an EKG, and the man was suffering from ventricular fibrillation.
They had a defibrillator and used it on him immediately. He converted, and I heard by the end of the day he was conscious in the hospital. The CPR and defibrillator saved his life.
I'd talk to my doctor about the need for one though. If your DH is suffering from AFIB, the biggest concern is for a stroke due to blood clots. So hopefully, he's taking his medications. A defibrillator is not normally used for AFIB.
If the doctor recommends it can not only save one of you, but a stranger who is in dire need also. Just make sure you receive proper training on CPR and correct use of the machine.