Aim: 

Our aim was to investigate the effect of physical training on atrial refractoriness and the implication of postganglionic parasympathetic neurons in isolated heart.

Methods: 

The study was performed in 16 New Zealand rabbits which were assigned to a control (n=5), a sham operated (n=6) and a trained (n=5) groups. During the 6 weeks of training period, five rabbits were exercised following a chronic exercise protocol on treadmill, while the other groups remained in the animal quarters. After these 6 weeks, rabbits were anaesthetized, sacrificed and their hearts excised and isolated in a Langendorff system. Pacing and recording electrodes were positioned on left atria. Extrastimulus test, using four different pacing cycle lengths (10% less than the basal cycle length, 250, 200 and 150ms) was carried out before and after the infusion of atropine (1mM). Atrial effective (AERP) and functional (AFRP) refractory periods were determined to assess atrial refractoriness. To analyze the effects of parasympathetic blocking on refractoriness, an ANOVA test (repeated measures) was applied.

Results: 

In the sham operated group, both AERP and AFRP did not change with time. AERP was longer (p<0.05) in the trained group than in the control group (i.e. 72.22.78 versus 60.758.54ms at 250ms of pacing cycle length). AERP and AFRP did not change after atropine administration, in control and trained groups.

Conclusion: 

Chronic physical exercise seems to increase atrial refractoriness. Since atrial refractory periods were not modified after atropine, the mechanism underlying could be intrinsic in nature.

Supported by MEC (DEP2007-73234-C03-01) and Generalitat Valenciana (BFPI/2008/003).