Optical Mapping in a New Guinea Pig Model of Ventricular Tachycardia Reveals Mechanisms for Multiple Wavelengths in a Single Reentrant Circuit

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Abstract
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 (2×10 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.