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.

Digital here means “using fingers” rather than “not analog”, right?

Would the reverse be to use the anal-log?