"Chronic excessive exercise has been consistently associated with increased risks of atrial fibrillation (AF)" Happened to me. I am convinced my Afib was/is the result of my hard charging CrossFit type workouts, especially as I aged. At 64 it all went to shit. Took nearly a year and a half to fully recover to a point where I could have a decent workout. Not too much hard cardio type workouts these days, especially for duration. 2-3 days a week in the gym and maybe one of those is what I would call intense. Most everything is resistance training with the occasional heavy bag/shadow boxing thrown in, but never more than 20 minutes of that. At 70+ it's about management of working with what you have. The days pf PR's are long gone.
I'm 64 now, and wondering if my past might catch up with me. While I was never into endurance work per se, I did do a half hour of fairly intense "cardio" after my too-long weight workouts in years gone by.
It always does, but if by 64 you haven't noticed anything unusual wear and tear, you probably won't. CrossFit is one of the stupidest sport one can do. Doctors and chiropractors love that sport...
I forgot to add that poor nutrition also played a role in my Afib. At 62 I decided to get lean to the max and went on a crazy diet which didn't provide enough nutrients. Combining both the poor diet, hard charging workouts and doing those 6 days a week led to disaster. Keep telling myself suck it up old man until I finally collapsed, literally. Took a trip to the ER followed by 3 more trips to the ER over a six month period to get it through my thick f'n skull I was on the wrong path.