Right Ventricular Myocardial Mechanics: Multi-Modal Deformation, Microstructure, and Modeling

The right ventricular myocardium, much like the rest of the right side of the heart, has been consistently understudied. Presently, little is known about its mechanics, its microstructure, and its constitutive behavior. In this work, we set out to provide the first data on the mechanics of the right ventricular myocardium in both simple shear and uniaxial loading. To this end, we tested ovine tissue samples under a comprehensive mechanical testing protocol that consisted of six simple shear modes and three tension/compression modes. After mechanical testing, we conducted a histology-based microstructural analysis on each sample that yielded high resolution fiber distribution maps across the entire sample thickness. Equipped with this detailed mechanical and histological data, we employed an inverse finite element framework to determine the optimal form and parameters for microstructure-based constitutive models. The results of our study show that right ventricular myocardium exhibits nonlinear, anisotropic, tension/compression asymmetric behavior with negative Poynting effect and minimal hysteresis. In addition, we found that myocardial fibers changes angles transmurally and are dispersed within the fiber-sheet direction. Through our inverse finite element analysis, we found that the Holzapfel model successfully fits these data, even when selectively informed by rudimentary microstructural information. And, we found that the inclusion of higher-fidelity microstructural data improved the Holzapfel model's predictive ability. Looking forward, this investigation is a critical step towards understanding the fundamental mechanical behavior of right ventricular myocardium, and lays the groundwork for future whole-organ mechanical simulations.