Aim: 

To investigate the effects of chronic exercise on myocardial electrophysiological heterogeneity (closely related with re-entrant arrhythmias) and its modification by myocardial ischemia.

Methods: 

Perfused rabbit hearts were used. Eight rabbits were submitted to a running program on motor-driven treadmill for 6 weeks (5 days/wk) (trained group). Ten rabbits were housed during the same period than the exercise protocol (control group). After training or housing, the rabbits were anaesthetized, killed and the hearts excised, isolated and connected to a Langendorff system. A pacing electrode and a plaque with 256 recording electrodes were positioned on the left ventricle for recording. ventricular fibrillation (VF) was triggered, pacing at increasing frequencies, five minutes before the coronary artery occlusion (CAO). Dominant frequency (DF) of VF was determined by a spectral analysis. Mean DF of VF and its standard deviation were determined to calculate the variation coefficient (VC) in each experiment, as index of heterogeneity. Determinations were carried out immediately after VF triggering, immediately before CAO (basal) and after CAO (just after and 15, 30, 45, 60, 90, 120, 150, 180, 210, 240, 270 and 300 seconds after the occlusion). A repeated measures ANOVA test was used to compare all values. p<0.05 was considered significant.

Results: 

No differences were observed in VC before CAO in both groups. VC increased after CAO in both groups. Nevertheless, although slight, fewer differences were observed in VC in the trained group after CAO.

Conclusions: 

Physical training could protect against acute myocardial ischemia, decreasing slightly the electrophysiological heterogeneity.

Supported by MEC (DEP2006-56208-C03-01 and SAF2007-62412).