Finite-Element Extrapolation of Myocardial Structure Alterations Across the Cardiac Cycle in Rats

Abstract

Myocardial microstructures are responsible for key aspects of cardiac mechanical function. Natural myocardial deformation across the cardiac cycle induces measurable structural alteration, which varies across disease states. Diffusion tensor magnetic resonance imaging (DT-MRI) has become the tool of choice for myocardial structural analysis. Yet, obtaining the comprehensive structural information of the whole organ, in 3D and time, for subject-specific examination is fundamentally limited by scan time. Therefore, subject-specific finite-element (FE) analysis of a group of rat hearts was implemented for extrapolating a set of initial DT-MRI to the rest of the cardiac cycle. The effect of material symmetry (isotropy, transverse isotropy, and orthotropy), structural input, and warping approach was observed by comparing simulated predictions against in vivo MRI displacement measurements and DT-MRI of an isolated heart preparation at relaxed, inflated, and contracture states. Overall, the results indicate that, while ventricular volume and circumferential strain are largely independent of the simulation strategy, structural alteration predictions are generally improved with the sophistication of the material model, which also enhances torsion and radial strain predictions. Moreover, whereas subject-specific transversely isotropic models produced the most accurate descriptions of fiber structural alterations, the orthotropic models best captured changes in sheet structure. These findings underscore the need for subject-specific input data, including structure, to extrapolate DT-MRI measurements across the cardiac cycle.

Review of cardiac–coronary interaction and insights from mathematical modeling

“…A model that considers nonlinear elasticity of the passive myocardium was developed subsequently (Janz et al, 1974). Thereafter, FE model describing cardiac mechanics has rapidly evolved and become more advanced with the inclusion of time‐dependent active contraction behavior of the cardiac muscle (Fan et al, 2023; Guccione et al, 1995, 2003), viscoelastic response of the tissue (Nordsletten et al, 2021), detailed tissue microstructure (Gomez et al, 2015; Lanir, 1980; Xi et al, 2019; Young et al, 2008), as well as its coupling with other physics (i.e., electrophysiology; Arumugam et al, 2019; Fan, Choy, et al, 2021; Lee, Sundnes, et al, 2016), hemodynamics (Kerckhoffs et al, 2007), growth and remodeling (Shavik et al, 2021). The mechanical behavior of cardiac muscle/tissue can be separated into its passive behavior and its active behavior, which can be described using an active stress formulation or an active strain formulation (Ambrosi & Pezzuto, 2012).…”

Right Ventricular Fiber Structure as a Compensatory Mechanism in Pressure Overload: A Computational Study

“…Support material followed a coupled neo-Hookean formulation with stiffness coefficient set at 0.1 kPa and a Poisson ratio of zero. The support strategy provides numerical stability, but has a negligible effect in cavity volumes (an increase, or decrease, in support stiffness by a factor of 10 resulted in less than 0.01% change in ventricular volume [37]).…”