Can someone translate this into English for the ones who aren’t doctors or biologists?

This sounds like someone was having a heart attack and they started playing with his butthole. I’d appreciate if someone could tell me that’s not the case.

You're pretty much correct. AF is a heart rhythm abnormality, and if it persists, like it seems to here, it renders the heart unable to pump blood. It appears he might have been undergoing a prostate exam when this happened, since that's the usual reason for a digital rectal exam. You'd have to assume the doctor knew they had this condition to begin with.

Nope. If I recall correctly all other interventions failed, so this was a hail Mary that happened to work

Interesting. That area of the body is pretty sensitive, I can see how it might generate enough sensation to affect other areas of the body.