Dispersion-based reentry: mechanism of initiation of ventricular tachycardia in isolated rabbit hearts

The aim of the study was to determine whether facilitation of reentry by po tassium-channel openers is related to dispersion of refractoriness and/or m odification of anisotropic properties of ventricular myocardium. The disper sion of ventricular effective refractory period (VERP), longitudinal and tr ansverse ventricular conduction velocities (theta L and theta T, respective ly), and wavelength [lambda = VERP x theta(L or T)] were studied in Langend orff-perfused left ventricular epicardium in 20 rabbits during infusion of incremental doses of levcromakalim or nicorandil. Dispersion of refractorin ess was assessed using standard deviation of VERP mean (SD-VERP), dispersio n index (DI; SD-VERP/mean VERP), and maximum dispersion (D-max = VERPmax - VERPmin). Ventricular conduction velocities and anisotropic ratio were not modified, whatever the dose used. VERP and lambda were significantly shorte ned at high concentrations of levcromakalim and nicorandil. At these doses, SD-VERP, DI, and D-max were increased significantly. Analysis of ventricul ar tachycardia induction, performed using a high-resolution ventricular map ping system, confirmed that heterogeneity and shortening of VERP were facto rs inducing functional conduction block. Our data suggest that, in rabbit l eft ventricular epicardium, functional conduction block facilitating the oc currence of reentry could be initiated by shortening and, especially, by di spersion of refractoriness during infusion of potassium-channel openers.