Shear properties of passive ventricular myocardium

TLDR

The study measured shear responses of passive ventricular myocardium from six pig hearts by cutting 3 mm cubes, applying up to 0.5 mm sinusoidal shear in two orthogonal directions, and recording forces across all six simple shear modes. Results show that passive myocardium exhibits nonlinear, viscoelastic, directionally dependent softening, with the least resistance in the plane of the layers and the greatest resistance when shear stretches the myocyte axis, indicating that elastic elements aligned with microstructural axes resist simple shear.

Abstract

We examined the shear properties of passive ventricular myocardium in six pig hearts. Samples (3 × 3 × 3 mm) were cut from adjacent regions of the lateral left ventricular midwall, with sides aligned with the principal material axes. Four cycles of sinusoidal simple shear (maximum shear displacements of 0.1–0.5) were applied separately to each specimen in two orthogonal directions. Resulting forces along the three axes were measured. Three specimens from each heart were tested in different orientations to cover all six modes of simple shear deformation. Passive myocardium has nonlinear viscoelastic shear properties with reproducible, directionally dependent softening as strain is increased. Shear properties were clearly anisotropic with respect to the three principal material directions: passive ventricular myocardium is least resistant to simple shear displacements imposed in the plane of the myocardial layers and most resistant to shear deformations that produce extension of the myocyte axis. Comparison of results for the six different shear modes suggests that simple shear deformation is resisted by elastic elements aligned with the microstructural axes of the tissue.