Exercise Dose Dependent Atrial Remodelling and Atrial Fibrillation

The dependence of atrial fibrillation (AF) on exercise dose is U shaped. To assess the physiological basis for this relationship, we swam 3 groups of CD1 mice at variable daily durations (120, 180 and 240 minutes per day) while ensuring that all mice received similar amounts of total exercise. To do this, we measured O2 consumption rates during swims and quantified exercise effort using volumes of O2 consumed during swimming. Consistent with comparable total exercise effort, all 3 groups showed similar reductions in body weight and similar changes in most ventricular parameters, despite a trend towards lower heart rates with increased swim durations. AF vulnerability, atrial fibrosis, atrial hypertrophy, and P-wave duration were associated with exercise dose, and we suggest that increases in atrial pressure that occur with longer exercise durations promote this remodelling. Collectively, our data demonstrate that AF vulnerability and adverse atrial changes rise as exercise duration increases.