Influence of cardiac tissue anisotropy on re-entrant activation in computational models of ventricular fibrillation

Abstract

Published paper Clayton, R.H (2009) Influence of cardiac tissue anisotropy on re-entrant activation in computational models of ventricular fibrillation. Physica D-Nonlinear Phenomena, AbstractThe aim of this study was to establish the role played by anisotropic diffusion in (i) the number of filaments and epicardial phase singularities that sustain ventricular fibrillation in the heart, (ii) the lifetimes of filaments and phase singularities, and (iii) the creation and annihilation dynamics of filaments and phase singularities. A simplified monodomain model of cardiac tissue was used, with membrane excitation described by a simplified 3-variable model. The model was configured so that a single re-entrant wave was unstable, and fragmented into multiple re-entrant waves. Re-entry was then initiated in tissue slabs with varying anisotropy ratio. The main findings of this computational study are: (i) anisotropy ratio influenced the number of filaments sustaining simulated ventricular fibrillation, with more filaments present in simulations with smaller values of transverse diffusion coefficient, (ii) each re-entrant filament was associated with around 0.9 phase singularities on the surface of the slab geometry, (iii) phase singularities were longer lived than filaments, and (iv) the creation and annihilation of filaments and phase singularities were linear functions of the number of filaments and phase singularities, and these relationships were independent of the anisotropy ratio. This study underscores the important role played by tissue anisotropy in cardiac ventricular fibrillation.

Vortex filament dynamics in computational models of ventricular fibrillation in the heart

“…22 The anatomically detailed model of rabbit ventricles was based on the dataset developed at the University of California-San Diego, 34 fitted to a regular Cartesian grid with a spacing of 0.25 mm. The cube geometry had dimensions of 50ϫ 50ϫ 50 mm 3 ͑7 762 392 grid points͒; the isotropic and anisotropic slabs had dimensions of 75.0ϫ 75.0 ϫ 17.5 mm 3 ͑6 038 672 grid points͒ and 79.5ϫ 79.5 ϫ 13 mm 3 ͑4 992 800 grid points͒, respectively.…”

“…16,17 Filaments with "positive tension" contract, whereas filaments with "negative tension" extend. 6 Filament dynamics have been documented in a number of computational studies, which have shown that for normal excitability and steep restitution, filaments tend to be short lived, 21,22 and that most filament creation arises from filament division rather than filament birth. 18 Negative filament tension is associated with reduced excitability, which in car-diac tissue mirrors some of the changes seen in myocardial ischemia.…”

“…23,28,29 The ventricular wall is anisotropic; cells are arranged in fibers than run almost parallel to the surface, and rotate by about 120°across the ventricular wall. Propagation along fibers is about twice as fast as propagation across fibers, and several numerical studies have shown that regional differences in fiber orientation can interact with membrane kinetics to create additional instability, resulting in increased numbers of filaments, 10,12,22,25 as well as influencing filament orientation. 30 The aim of this study was therefore to use numerical experiments to investigate systematically how kinetics, initial conditions, and tissue geometry affect the number of filaments, their size and orientation, and their lifetime during simulated VF.…”

Stochastic dynamics of phase singularities under ventricular fibrillation in 2D Beeler-Reuter model

“…7 type II NLE is estimated from the relation in Eq. (10). The other parameters are determined using Eq.(6).…”

“…During VF, many phase singularities (PSs) appear and, therefore, features such as lifetime, total number, and space-time trajectory of them may give new insights into VF. 10 In defect-mediated turbulence, the statistical properties of topological defects (phase singularities) have been studied to reveal the complex nature of the turbulence. [11][12][13][14][15] Gil et al 11 investigated creation and annihilation mechanisms of defect pairs and predicted the probability distribution function of the number of defect pairs in oscillatory media.…”