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 (λ) and path length importantly determines the stability of reentrant arrhythmias, the physiological determinants of λ are poorly understood. To investigate the cellular mechanisms that control λ during reentry, we developed an experimental system for continuously monitoring λ within a reentrant circuit with the use of voltage-sensitive dyes and a new guinea pig model of ventricular tachycardia (VT). Methods and Results: Action potentials were recorded simultaneously from 128 ventricular sites in Langendorff-perfused hearts (n=15) in which propagation was confined to a two-dimensional rim of epicardium by an endocardial cryoablating procedure. The reentrant path was precisely controlled by creating an epicardial obstacle (2x10 mm) with an argon laser. To control for fiber orientation and rate-dependent membrane properties, λ during reentry was compared with λ during plane wave propagation transverse and longitudinal to cardiac fibers at a stimulus 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. λ varied considerably within the reentrant circuit (range, 10.6 to 22.5 mm), because of heterogeneities of conduction rather than action potential duration. λ was significantly shorter during reentrant propagation (ie, with pivoting) parallel to fibers (10.6±4.2 mm) compared with plane wave propagation (ie, without pivoting) parallel to fibers (32.8±6.5 mm, P<.02), indicating that wave-front pivoting was primarily responsible for shortening of λ during reentry. The mechanism of λ shortening was conduction slowing from increased current load experienced by the pivoting wave front. Conclusions: We provide direct experimental evidence that multiple wavelengths are present even within a relatively simple reentrant circuit. Abrupt changes in loading during wave-front pivoting, rather than membrane ionic properties or fiber structure, were a major determinant of λ and, therefore, may play an important role in the stability of reentry.