Block of impulse propagation at an abrupt tissue expansion: evaluation of the critical strand diameter in 2- and 3-dimensional computer models

Abstract

. ___ .-_---_----Objective: Unidirectional conduction block in the heart can occur at a site where the impulse is transmitted from a small to a large tissue volume. The aim of this study was to evaluate the occurrence of conduction block in a 2-dimensional and 3-dimensional computer model of cardiac tissue consisting of a narrow strand abruptly emerging into a large area. In this structure, the strand diameter critical for the occurrence of block, h,, was evaluated as a function of changes in the active and passive electrical properties of both the strand and the large medium. M&hods: The effects of changes in the following parameters on h, were analysed: (I 1 maximum sodium conductance (gNa,,, 1, (21 longitudinal (R,) and transverse (R,) intracellular resistivities, and (3) inhomogeneities in gNa,,,, and R, and R," between the strand and the large area. Three ionic models for cardiac excitation described by Beeler-Reuter, Ebihara-Johnson, andLuo-Rudy ionic current kinetics were compared. Results: In the 2-dimensional simulations, h, was 175 pm in Ebihara-Johnson and Beeler-Reuter models and 200 pm in the Luo-Rudy model. At the critical strand diameter, the site of conduction block was located beyond the transition, i.e. a small circular area was activated in the large medium, whereas with narrower strands conduction block occurred within the strands. The decrease of gNa,,, resulted in a large increase of h,. This increase was mainly due to the change of d%7l,x in the large area, while h, was almost independent of giva,,, in the strand. Changing R, had no effect on h,, whereas the increase of R, decreased h, and reversed conduction block. Inhomogeneous changes of R, and R, in the strand versus the large medium had opposite effects on h,. When the resistivities of the strand alone were increased, h, also increased. In contrast, the increase of the resistivities in the large area reduced h,. In the 3-dimensional model, h, was 2.7 times larger than the corresponding Sdimensional values at the various levels of gNa,,, and resistivity. Conclusions: (1) At physiological values for active and passive electrical properties, h, in the 2D simulations is close to 200 pm in all three ionic models. In the 3-dimensional simulations, I?, is 2.7 larger than in the 2-dimensional models. (2) The excitable properties of the large area but not of the strand modify h,.. The decrease of intercellular coupling in the large medium facilitates impulse conduction and reduces h,., while the same change in the strand increases h,.. (3) Occurrence of conduction block at an abrupt geometrical transition can be explained by both the impedance mismatch at the transition site and the critical curvature beyond the transition.

Wave front fragmentation due to ventricular geometry in a model of the rabbit heart

“…25 Sources of heterogeneity in the heart might include differences in local electrophysiological properties due, for example, to uneven ion channel expression, or other forms of geometric heterogeneity such as curvature of muscle fibers, which we previously showed influences propagation in much the same way Gaussian curvature does, 20 or local tissue expansions, which also focus and disperse current. 26 Nonstationary reentrant propagation is probably the norm during VF 24,27,28 and multiple forms of heterogeneity-geometric and otherwisecertainly exist. Thus, this mechanism is probably present in real fibrillating hearts.…”

The Undetermined Geometrical Factors Contributing to the Transverse Conduction Block of the Crista Terminalis

“…We hypothesized that the CT steep slope would play an important role in causing the conduction block since it is known that the tissue geometry is one of the safety factors for conduction. 20,21 In both groups, the slope angle on the lateral side was steeper at the levels with block than at those without block during LRA pacing. Therefore, it may be possible that the steep CT slope was implicated in the CT transverse conduction block in this direction of conduction.…”

“…In addition, we hypothesized that the slope of the CT ridge as a geometrical factor for the conduction would be involved in the CT transverse conduction block because a steep change in the tissue geometry has been known to be one of the reduced safety factors for conduction. 20,21 However, it also still remains unknown whether or not such a geometrical parameter influences the CT transverse conduction.…”

Computational rabbit models to investigate the initiation, perpetuation, and termination of ventricular arrhythmia

“…In particular, it has been known that sites of tissue expansion could promote conduction block due to source-sink mismatch (Fast and Kleber, 1995a; Xie et al, 2010). The pro-arrhythmic effects of this mechanism was investigated in a computational study using the UCSD rabbit ventricular geometry (Boyle et al, 2014).…”