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Passive mechanics plays an important role during the electromechanically coupled cardiac cycle and its behaviour strongly changes after myocardial infarction. In the present work, the cardiac tissue is modelled as a mixture of an active orthotropic intact myocardium and a passive transversely isotropic fibrotic scar structure. We apply the constitutive model on the fully electromechanically coupled simulation of a cardiac cycle using a generic geometry of a rat left ventricle. Finally, the ejection fractions for various parameter sets based on the fitting to experimental data in different animal species as well as for a varying amount of fibrosis are compared. We show that both, the choice of species‐specific passive material parameters and the amount of fibrosis, have a significant influence on the cardiac performance measured by the ejection fraction of the left ventricle.

In the past decades, the structure of the heart, human as well as other species, has been explored in a detailed way e.g. via histological studies or diffusion tensor magnetic resonance imaging. Nevertheless, the assignment of the characteristic orthotropic structure of the material in a patient-specific finite element model remains a challenging task. Various types of rule-based models, which define the local fibre and sheet orientation depending on the transmural depth, have been developed. However, the correct assessment of the transmural depth is not trivial. Its accuracy has a substantial influence on the overall mechanical and electrical properties of the model. The main purpose of this study is the developement of a finite-element-based approach to accurately determine the transmural depth. We propose a finite-element-based discontinuous Galerkin approach to determine the transmural path, thickness and depth. Based on the accurate transmural depth, we assign the local material orientation of the orthotropic tissue structure in a usual fashion. We show that this approach leads to a more accurate definition of the transmural depth. Furthermore, for the left ventricle, we propose rules for the transmural fibre and sheet orientation by fitting them to literature based data. The proposed functions show a distinct improvement compared to existing rules.