Key result
In a mathematical model of atrial tissue, increasing myocyte-fibroblast coupling led to action potential propagation block at critical fibroblast densities, which varied based on the spatial distribution of fibroblasts.
Why the study?
The roles of electrical coupling between myocytes and fibroblasts and the spatial distribution of fibroblasts in triggering and sustaining cardiac arrhythmias are poorly understood.
This computational study provides a theoretical framework and analytical expressions to accurately predict action potential propagation block caused by myocyte-fibroblast coupling in atrial tissue.
Model predicts fibroblast patterns modulate atrial conduction; leaves open experimental validation before any clinical relevance.
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 idealized 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 idealized 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.
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Mortensen et al. (2021) studied Cardiac arrhythmias (simulated atrial tissue). Myocyte-fibroblast electrical coupling and fibroblast distribution vs. Uncoupled myocytes (intact myocardium) was evaluated on Action potential propagation block and conduction velocity. In a mathematical model of atrial tissue, increasing myocyte-fibroblast coupling led to action potential propagation block at critical fibroblast densities, which varied based on the spatial distribution of fibroblasts.
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