Objectives: 

Little is known about the effects of chronic exercise on the intrinsic electrophysiological heterogeneity of ventricular myocardium and the involvement of myocardial cholinergic neurons on this property. This question is interesting from the physiological and pathophysiological standpoint, to the extent that electrophysiological heterogeneity is one of the parameters most directly involved in the establishment, maintenance and termination of reentrant arrhythmias, such as ventricular fibrillation (VF). We hypothesize that exercise reduces the dispersion of ventricular refractoriness, as an expression of myocardial electrophysiological heterogeneity, and modifies the effect of cholinergic neurons on this parameter.

Materials: 

Eight NZW rabbits were submitted to a six-weeks training protocol and nine were housed. After this period, rabbits were anesthetized (ketamine 10mg/kg i.v.), euthanized and the hearts excised, isolated and perfused in a Langendorff system. A pacing electrode and a plaque with 256 recording electrodes were positioned on the left ventricle. VF was induced at increasing frequencies. It was determined the functional refractory period during the VF (FRPVF) in each electrode (as the 5th percentile of the VF cycle length histogram), and its coefficient of variation (CVFRP): FRPVF SD/FRPVF mean. Determinations were performed 5min after VF triggering and 5min after atropine(1mM). An ANOVA test (one factor) was applied to compare CVFRP between and within groups, before and after atropine infusion. Significance when p<0,05.

Results: 

CVFRP was higher in control group before (15,6±3,6%;n=9vs. 12,5±1,5%;n=8) and after (12,8±2,5%vs.10,8±2,2%) atropine, and decreased after atropine only in control group (15,6±3,6% vs.12,8±2,5%).

Conclusions: 

Chronic exercise decreases electrophysiological heterogeneity. Although cholinergic myocardial neurons seem to modify this property, training could prevent this intrinsic neural implication.

Support: DEP2007-73234-C03-01, Prometeo 2010-093