Increased atrial arrhythmia susceptibility induced by intense endurance exercise in mice requires TNFα

Atrial fibrillation (AF) is the most common supraventricular arrhythmia that, for unknown reasons, is linked to intense endurance exercise. Our studies reveal that 6 weeks of swimming or treadmill exercise improves heart pump function and reduces heart-rates. Exercise also increases vulnerability to AF in association with inflammation, fibrosis, increased vagal tone, slowed conduction velocity, prolonged cardiomyocyte action potentials and RyR2 phosphorylation (CamKII-dependent S2814) in the atria, without corresponding alterations in the ventricles. Microarray results suggest the involvement of the inflammatory cytokine, TNF alpha, in exercised-induced atrial remodelling. Accordingly, exercise induces TNF alpha-dependent activation of both NF kappa B and p38MAPK, while TNF alpha inhibition (with etanercept), TNF alpha gene ablation, or p38 inhibition, prevents atrial structural remodelling and AF vulnerability in response to exercise, without affecting the beneficial physiological changes. Our results identify TNF alpha as a key factor in the pathology of intense exercise-induced AF.