Virtual electrode polarization-induced reentrant activity

Abstract

It is known that electric shocks create a characteristic pattern of polarization ('virtual electrode polarization') in the myocardium but its roles on post-shock excitations remain to be clarified. Optically has been mapped electrical activity of the left ventricular subepicardial layer of Langendorff-perfused rabbit hearts endocardialy frozen. Monophasic anodal and cathodal shocks were applied during the plateau or repolarization phase of the action potential. Electric shocks (20 V, 10 ms) resulted in a 'dog-bone' pattern of polarization around the stimulation electrode and the withdrawal of the shocks were followed by 'break excitations'. Spread of the break excitations were partially blocked by refractory of the preceding excitation, and slow conduction around the functional line of block initiated reentrant excitations. These results suggest that break excitations arising from the virtual electrode polarization combined with spatial heterogeneity in repolarization of the preceding excitation play important roles in the genesis of post-shock reentrant activities.