Aim: 

To test if chronic physical training modifies the minimal pacing frequency to produce ventricular fibrillation in isolated rabbit heart and the role that postganglionic parasympathetic neurons could play in this effect.

Method: 

Nine rabbits were exercised during 6 weeks following a chronic exercise protocol on treadmill (trained group) and another eleven rabbits (control group) were housed during the same period. When the chronic exercise program was finished, rabbits were anaesthetized, sacrificed and their 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. Ventricular fibrillation was produced by pacing (computerized system) at increasing frequencies (2 Hz·min^-1), starting from 4 Hz until ventricular fibrillation was induced. Stimuli of 2 ms duration and three times the diastolic threshold (155mA) intensity were used. This protocol was performed before and after the infusion of atropine (1mM). A record was obtained from the start of pacing, and specific software was used to measure the frequency of pacing that generated ventricular fibrillation. Paired and unpaired t test were applied to compare the pacing frequency between and within groups, respectively.

Results: 

The pacing frequency was 13.50.94 Hz in control group and 14.10.72 Hz in the trained group (p=0.182). Similar results were obtained after atropine administration and no differences were obtained, both between and within groups.

Conclusion: 

The inducibility of ventricular fibrillation by pacing does not seem to be dependent on chronic physical exercise or parasympathetic postganglionic neurons activity.

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