Mine, they ended up calling "idiopathic." Meaning after test after blood draw and test after test after blood draw after blood draw, they never could figure it out.
I used to shoot competitively; bowling pins, three gun, free pistol, service pistol, silhouette, skeet & trap.. so I reloaded my own ammunition. We initially thought it was chemical exposure, so I started wearing a respirator and nitrile gloves, problem seemed to abate. Then one day I pulled the used tire wagon in by myself (worked in a tire store, we sold used tires off an old haywagon parked out front).. and lo and behold, I was in arrhythmia when I was done. Stress test, nuclear stress test, more stress testing.. still found nothing.
So I spent a couple years on lanoxin. Been off the med for 15 years now, no problems with arrhythmia, but in the meantime I did have a couple of stents put in..
Just last December released from Plavix daily.
Also started a new diet, went keto.
Lost 50 lbs so far.
Dr told me last month to add cardio.. I said "over and above my strength training?" "Yep."
So I dug the bike back out.. and remembered why I had put it away to begin with.. hardtails are hell on your backside when you are a Clydesdale.. Bought a couple vintage fs Cannondales.
It's a long road.
But the rewards are many.
Keep on your Dr. Find a cardiologist if you need to.