Cycle Length Dynamics and Spatial Stability at the Onset of Postinfarction Monomorphic Ventricular Tachycardias Induced in Patients and Canine Preparations

Abstract

Background The aim of this study was to determine whether cycle length (CL) variations at the onset of monomorphic ventricular tachycardias follow distinctive patterns. Methods and Results We retrospectively analyzed 59 monomorphic ventricular tachycardias induced in 40 patients in whom intraoperative mapping was performed with 63 epicardial and 64 endocardial electrograms recorded simultaneously. Activation times and CL were determined at each electrode site over several beats (36±10 beats, mean±SD) starting with the first after programmed stimulation. In the majority of the tachycardias, CL variations were accounted for by fitting to an exponential function: CL=CL s +A e − b/τ , where CL s is the stable CL, b is beat number, τ is the time constant (in beat number), and A is the magnitude of CL relaxation. A decelerating trend (with reference to rate) (negative A) accounted for 21 tachycardias, an accelerating trend in rate (positive A) accounted for 12 tachycardias, and 4 others displayed a double dynamic behavior, with an initial acceleration followed by a decelerating trend in rate. Among the ventricular tachycardias that were not fitted to exponential models, 12 showed a constant trend and 10 others showed irregular CL fluctuations. The monomorphic character of the tachycardias was established by principal-component analysis, which also indicated that CL dynamics associated with the accelerating and decelerating trends may be related to shortening or prolongation of activation times, respectively, occurring in equal proportion at all recording sites. In canine preparations in which reentry circuits could be mapped with high resolution, CL showed an accelerating trend in rate when circus movement of excitation occurred around a transmural scar in muscle generating unipolar electrograms with relatively high −dV/dt max , and a decelerating trend in rate occurred when functional reentry occurred in muscle generating unipolar electrograms with depressed −dV/dt max . Conclusions Beat-to-beat CL variations may occur at the onset of sustained monomorphic ventricular tachycardia as a result of uniform acceleration or deceleration of activation times while the overall activation pattern remains constant. The associated initial trends in the rate of sustained monomorphic ventricular tachycardia follow typical patterns that might provide “signatures” corresponding to reentry substrates with distinctive functional properties.