Modelling thermo-electro-mechanical effects in orthotropic cardiac tissue

TL;DR

This paper introduces a comprehensive mathematical model for cardiac tissue that incorporates thermo-electro-mechanical effects, nonlinear conductivity, and active contraction, enabling simulation of complex phenomena like ventricular fibrillation.

Contribution

It presents a novel orthotropic active strain model combined with a mixed-primal finite element method for simulating cardiac tissue dynamics under multiple physical influences.

Findings

Thermo-electric effects significantly influence cardiac dynamics.

The model can reproduce pathological chaotic behaviors like fibrillation.

The finite element method effectively captures complex multiphysics interactions.

Abstract

In this paper we introduce a new mathematical model for the active contraction of cardiac muscle, featuring different thermo-electric and nonlinear conductivity properties. The passive hyperelastic response of the tissue is described by an orthotropic exponential model, whereas the ionic activity dictates active contraction incorporated through the concept of orthotropic active strain. We use a fully incompressible formulation, and the generated strain modifies directly the conductivity mechanisms in the medium through the pull-back transformation. We also investigate the influence of thermo-electric effects in the onset of multiphysics emergent spatiotemporal dynamics, using nonlinear diffusion. It turns out that these ingredients have a key role in reproducing pathological chaotic dynamics such as ventricular fibrillation during inflammatory events, for instance. The specific structure of the governing equations suggests to cast the problem in mixed-primal form and we write it in terms of Kirchhoff stress, displacements, solid pressure, electric potential, activation generation, and ionic variables. We also propose a new mixed-primal finite element method for its numerical approximation, and we use it to explore the properties of the model and to assess the importance of coupling terms, by means of a few computational experiments in 3D.