An electromechanical model of cardiac tissue: constitutive issues and electrophysiological effects.
ABSTRACT We present an electromechanical model of myocardium tissue coupling a modified FitzHugh-Nagumo type system, describing the electrical activity of the excitable media, with finite elasticity, endowed with the capability of describing muscle contractions. The high degree of deformability of the medium makes it mandatory to set the diffusion process in a moving domain, thereby producing a direct influence of the deformation on the electrical activity. Various mechano-electric effects concerning the propagation of cylindrical waves, the rotating spiral waves, and the spiral breakups are discussed.
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ABSTRACT: Elastic-electroactive (EA) media represent a wide range of materials and physical systems sensitive to mechanical forces and electric fields, in which time and temperature dependence are additional recurrent features. The behavior of fiber reinforced active tissues, namely the excitation-contraction coupling, is basically due to the nonlinear interplay between the passive elastic tissue and the active muscular network. The observed macroscopic dynamics derives as the emergent behavior of a complex multiscale architecture spanning several length scales. We present a general theoretical framework for the formulation of constitutive equations for viscous electro-active media. The approach is based on the additive decomposition of the Helmholtz free energy in elastic, viscous and active parts accompanied to the multiplicative decomposition of the deformation gradient in elastic, viscus and active parts. We describe a thermodynamically sound scenario that accounts for geometric and material nonlinearities. We specialize the material model to the behavior of colonic intestine tissue, and simulate the visco-electro-active behavior of the fiber-reinforced wall layers by using the finite element method.
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ABSTRACT: The objective of this work is to reveal the influence of the experimentally observed passive viscous behaviour of the myocardium on the electromechanical activity by making use of computational approaches. For this purpose, we adopt the fully implicit finite element framework and the passive response is described by the orthotropic viscoelastic material model. The capabilities of the proposed model are assessed by comparing finite element simulations of spiral waves in a heart tissue for the elastic and viscoelastic formulations. The results obtained indicate that rate effects in the passive myocardium play a significant role on the active myocardium response by decreasing the electrical wave speed which consequently effects the evolution of spiral waves. We further investigate the influence of viscosity on the defibrillation phenomenon by means of a three-field coupled finite element formulation of bidomain electromechanics.12/2015; 12. DOI:10.1016/j.piutam.2014.12.014
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ABSTRACT: Heart failure with preserved ejection fraction (HFpEF) accounts for about 50% of heart failure cases. It has features of incomplete relaxation and increased stiffness of the left ventricle. Studies from clinical electrophysiology and animal experiments have found that HFpEF is associated with impaired calcium homeostasis, ion channel remodeling and concentric left ventricle hypertrophy (LVH). However, it is still unclear how the abnormal calcium homeostasis, ion channel and structural remodeling affect the electro-mechanical dynamics of the ventricles. In this study we have developed multiscale models of the human left ventricle from single cells to the 3D organ, which take into consideration HFpEF-induced changes in calcium handling, ion channel remodeling and concentric LVH. Our simulation results suggest that at the cellular level, HFpEF reduces the systolic calcium level resulting in a reduced systolic contractile force, but elevates the diastolic calcium level resulting in an abnormal residual diastolic force. In our simulations, these abnormal electro-mechanical features of the ventricular cells became more pronounced with the increase of the heart rate. However, at the 3D organ level, the ejection fraction of the left ventricle was maintained due to the concentric LVH. The simulation results of this study mirror clinically observed features of HFpEF and provide new insights toward the understanding of the cellular bases of impaired cardiac electromechanical functions in heart failure.Frontiers in Physiology 03/2015; 6(78):1-14. DOI:10.3389/fphys.2015.00078