Efectes electrofisiològics miocàrdics intrínsecs sobre l'automatisme. La conducció i la refractarietat produïts per la realització d'un protocol d'entrenament. Estudi experimental.
Aim: To study the intrinsic electrophysiological myocardium modifications produced by chronic exercise in isolated rabbit heart. Methods: Two groups of New Zealand rabbits were studied. One group of rabbits (trained group, n=15) was trained on a motor-driven treadmill following a protocol (running velocity 0.33 m·s-1) and another group of rabbits (control group, n=12) was housed in the animal quarters for the same number of days as the training protocol duration. The electrophysiological parameters investigated in an isolated perfused rabbit heart were: a) basic sinus cycle length, atrioventricular conduction and ventricular conduction velocity; b) atrial, ventricular, atrioventricular and ventriculoatrial effective and functional refractory periods were obtained using the extrastimulus technique at four different pacing cycle lengths; c) mean, maximum, and minimum dominant frequencies of the induced ventricular fibrillation were also investigated using a spectral method; d) wave length. In vivo heart rate, myocardial heat shock proteins (HSP60), inducible nitric oxide synthetase (iNOS) and lactate concentration were also determined as electrophysiological and biochemical markers of training. Results: The following parameters were larger (p< 0.05) in trained group vs control group: atrioventricular conduction, wave length, atrioventricular functional refractory periods, ventricle effective and functional refractory periods, basic sinus cycle length, HSP60 and iNOS expression values. The mean dominant frequency of the ventricular fibrillation was lesser in trained group than control group and the rest of parameters did not change. Conclusion: Training seems to increase the electrical stability of ventricular myocardium. As the electrophysiological modifications were exhibited in hearts not submitted to extrinsic nervous system or humoral influences, they are, at least in part, intrinsic modifications. These electrophysiological data also suggest that aerobic training could protect against reentrant ventricular arrhythmias.
