Two, articles, one from Germany and one from Italy might provide some reassurance to long time endurance athletes worried about too much of a good thing damaging the heart.
Bohn et al from Germany reported a group of long term endurance athletes with many years of endurance exercise history whose extensive cardiac evaluation showed nothing to suggest that ARVC is a problem.
Pelliccia and co workers studied 1777 active competitive athletes and described echo findings and concluded their tendency to have somewhat larger left atria represented physiological adaptation which is largely without adverse clinical consequences and found a fib to be uncommon, less than 1% and similar to that of the general population. He also concluded that left and right ventricular exercise induced remodeling were basically balanced.This conflicts with some of the work of La Gerche and Heidbuchel who postulate that the right ventricle is less well designed that is the left ventricle for endurance exercise and and predisposes it to arrhythmias arising from right ventricular remodeling . But finding a bunch of white swans does not preclude the existence of black ones.
The case control studies reporting hazard ratios of 4 and five in regard to atrial fibrillation in long time endurance athletes ( and the meta analysis that summed them up with some statistical trappings) just might be vulnerable to selection bias while these two studies just might be vulnerable to survivor bias.