Atrial automaticity and atrioventricular conduction in athletes: contribution of autonomic regulation

Little is known about the sinoatrial automatism and atrioventricular conduc tion of trained individuals who present a normal resting electrocardiogram. We used transesophageal atrial stimulation, a minimally invasive technique , to evaluate aerobically trained athletes (n = 10) and sedentary individua ls (n = 10) with normal resting electrocardiograms, to test the hypothesis that parasympathetic tone, as detected by heart rate variability, could be associated with changes in sinoatrial automatism and atrioventricular condu ction. Corrected sinus node recovery time tended to be longer in athletes t han in sedentary individuals, but this difference did not reach statistical significance. The Wenckebach point occurred at a lower rate in athletes th an in the controls. Over a 24-h period of measurement, the mean RR interval was longer in the athletes than in the sedentary individuals. The mean squ are root of successive differences (rMSSD) tended to be higher in athletes than in controls, but this difference did not reach statistical significanc e. There was a moderate correlation (r = 0.48, P < 0.05) between the index of atrioventricular conduction, the rate at the Wenckebach point, and the l ogarithmically transformed rMSSD. Thus, as a corollary to its effects on th e sinus node, where increased parasympathetic tone, decreased sympathetic t one, and non-autonomic components may contribute to sinus bradycardia, it i s possible that athletic training may also induce intrinsic adaptations in the conduction system, which could contribute to the higher prevalence of a trioventricular conduction abnormalities observed in athletes.