OPTICAL MAPPING IN A NEW-GUINEA PIG MODEL OF VENTRICULAR-TACHYCARDIA REVEALS MECHANISMS FOR MULTIPLE WAVELENGTHS IN A SINGLE REENTRANT CIRCUIT

Background Although the relationship between cardiac wavelength (lambd a) and path length importantly determines the stability of reentrant a rrhythmias, the physiological determinants of lambda are poorly unders tood. To investigate the cellular mechanisms that control lambda durin g reentry, we developed an experimental system for continuously monito ring lambda within a reentrant circuit with the use of voltage-sensiti ve dyes and a new guinea pig model of ventricular tachycardia (VT). Me thods and Results Action potentials were recorded simultaneously from 128 ventricular sites in Langendorff-perfused hearts (n=15) in which p ropagation was confined to a two-dimensional rim of epicardium by an e ndocardial cryoablating procedure. The reentrant path was precisely co ntrolled by creating an epicardial obstacle (2x10 mm) with an argon la ser. To control for fiber orientation and rate-dependent membrane prop erties, lambda during reentry was compared with lambda during plane wa ve propagation transverse and longitudinal to cardiac fibers at a stim ulus cycle length (CL) comparable to the VT CL. Reentrant VT (CL=97.0/-6.2 ms) was reproducibly induced by programmed stimulation in 93% of preparations. lambda varied considerably within the reentrant circuit (range, 10.6 to 22.5 mm), because of heterogeneities of conduction ra ther than action potential duration. lambda was significantly shorter during reentrant propagation tie, with pivoting) parallel to fibers (1 0.6+/-4.2 mm) compared with plane wave propagation tie, without pivoti ng) parallel to fibers (32.8+/-6.5 mm, P<.02), indicating that wave-fr ont pivoting was primarily responsible for shortening of lambda during reentry. The mechanism of lambda shortening was conduction slowing fr om increased current load experienced by the pivoting wave front. Conc lusions We provide direct experimental evidence that multiple waveleng ths are present even within a relatively simple reentrant circuit. Abr upt changes in loading during wave-front pivoting, rather than membran e ionic properties or fiber structure, were a major determinant of lam bda and, therefore, may play an important role in the stability of ree ntry.