I just now noticed this thread, so I'll add some of my experience that may or not be relevant.
A couple of years ago (at age 72) I was scheduled for prostate cancer surgery and went to my primary physician for pre-op clearance. He did an EKG but no one read it before I left the office. The next day I was out on my boat free dive spearfishing, and just before I jumped in the water, I got a call telling me that I had to come back for another EKG. I told them that I was diving and would come in the next day, but they seemed to think it was important. So while I did dive a couple of spots, I went in early so as to get to the office before it closed. Another EKG confirmed that I had atrial flutter, which is a milder form of a a fib. My impression is that with flutter the atria beat at a constant rapid rate, while with fibrillation the rate is variable. They seemed surprised that I hadn't noticed any ill effects, but I hadn't. My only clue was that my pulse was around 75, and that was weird because its normally around 38. Apparently my atria were beating at 250 and the ventricles had chosen to beat at one fourth of that rate.
I was referred to an electrophysiologist. He said that cardioversion seldom fixed the problem for more than a few months and I didn't like the idea of drugs, so he did an ablation. A hot wire is threaded into your heart from an artery in your groin. The tissue that is causing the short circuit is found and then destroyed by electrical current. It worked. I was back to diving in a couple of weeks.
Than almost a year later I was schedule for more surgery and had another pre-op clearance, and sure enough my flutter had returned, so the guy did another ablation. Rather than wait until I'm scheduled for some other future surgery, he has me come in for an EKG every three months, and so far I'm fine. Both the atria and ventricles are ticking along in the high 30 beats per minute.
I'm not sure this has added anything of value, but I won't bill you.