Efectos electrofisiológicos miocárdicos intrínsecos producidos por la inhibición del sistema de intercambio sodio-potrón, en condiciones de normoxia, y tras la isquemia miocárdica regional. Estudio experimental.

by Such Miquel, Luis

ABSTRACT We have investigated the protective effects of the sodium-proton exchanger (NHE) inhibition using 5-(N-ethyl-N-isopropyl) amiloride (EIPA) 0.4 ?M, on the incidence of induced ventricular fibrillation (VF), and on intrinsic ventricular refractoriness, after circumflex coronary artery occlusion. Experiments were performed on isolated rabbit heart. To induce VF extrastimulus test with one, two and three extrastimuli, was used; the first extrastimulus application also served to determine refractory periods. Parameters were determined previously and after coronary occlusion, in both control and EIPA 0.4 ?M treated groups. In order to investigate whether the NHE inhibition produces some myocardial intrinsic electrophysiological effect, we have also investigated using EIPA, 0.4 and 1 ?M, in normoxic condition: a) the sinus cycle length and sinus node recovery time, as an automatism index; b) the sinoatrial conduction (Narulas test), and atrioventricular (AV) and ventricleatrial conduction, by anterograde and retrograde Wenckebach cycle length determination respectively; c) atrial, ventricular, and AV conduction system, effective and functional refractory periods using the extrastimulus test; and d) mean, minimum and maximum dominant frequency (DF) of VF by the Welchs method, which are properties closely related with ventricular refractoriness. NHE inhibition with 0.4 ?M protected the ischemic myocardium, decreasing VF inducibility, at least in part, by the maintenance of ischemic myocardium refractoriness, observed in this study. No modification on refractoriness was observed, in normoxic conditions, except an AV conduction system effective refractory period increase, with EIPA 1 ?M. The DF of VF was either not modified. EIPA 0.4 and 1 ?M also slightly depressed sinus chronotropism and AV conduction.