Action potential propagation and block in a model of atrial tissue with myocyte-fibroblast coupling

TL;DR

This study combines simulations and asymptotic theory to analyze how fibroblast distribution affects electrical propagation and block in atrial tissue, providing insights into arrhythmia mechanisms.

Contribution

It extends an asymptotic theory to model the effects of different fibroblast distributions on action potential propagation and block in atrial tissue.

Findings

Propagation block occurs at critical fibroblast parameters.

The asymptotic model accurately predicts propagation block.

Biomarkers like conduction velocity are estimated and validated.

Abstract

The electrical coupling between myocytes and fibroblasts and the spacial distribution of fibroblasts within myocardial tissues are significant factors in triggering and sustaining cardiac arrhythmias but their roles are poorly understood. This article describes both direct numerical simulations and an asymptotic theory of propagation and block of electrical excitation in a model of atrial tissue with myocyte-fibroblast coupling. In particular, three idealised fibroblast distributions are introduced: uniform distribution, fibroblast barrier and myocyte strait, all believed to be constituent blocks of realistic fibroblast distributions. Primary action potential biomarkers including conduction velocity, peak potential and triangulation index are estimated from direct simulations in all cases. Propagation block is found to occur at certain critical values of the parameters defining each idealised fibroblast distribution and these critical values are accurately determined. An asymptotic theory proposed earlier is extended and applied to the case of a uniform fibroblast distribution. Biomarker values are obtained from hybrid analytical-numerical solutions of coupled fast-time and slow-time periodic boundary value problems and compare well to direct numerical simulations. The boundary of absolute refractoriness is determined solely by the fast-time problem and is found to depend on the values of the myocyte potential and on the slow inactivation variable of the sodium current ahead of the propagating pulse. In turn, these quantities are estimated from the slow-time problem using a regular perturbation expansion to find the steady state of the coupled myocyte-fibroblast kinetics. The asymptotic theory gives a simple analytical expression that captures with remarkable accuracy the block of propagation in the presence of fibroblasts.