Workers’ compensation — Compensable accidents — Presumption of compensability — Heart disease — Correctional officer — Trigger theory — Where medical evidence showed that claimant’s peak exercise workouts in 2002 triggered degeneration of his congenital heart condition into atrial fibrillation, but this evidence wasn’t evaluated as a non-occupational cause that would overcome statutory presumption of compensability, reversal of compensation order entered in favor of claimant and remand for further consideration of trigger theory in view of exercise-related evidence is appropriate — Discussion of “trigger theory”