A Microstructurally Based Multi-Scale Constitutive Model of Active Myocardial Mechanics

Contraction of cardiac muscle cells provides the work for ventricular pumping. The primary component of this contractile stress development in myocardium acts along the axis of the myofilaments; however, there may be a component directed transversely as well. Biaxial testing of tonically activated cardiac tissue has shown that myocardium can generate active stresses in the transverse direction that are as high as 50% of those developed along the fiber axis. The microstructural basis for this is not clear. We hypothesized that transverse active stresses are generated at the crossbridge and myofilament lattice scales and transmitted via the myocardial laminar sheets as plane stress objects. To test this hypothesis, we developed a multi-scale constitutive model accounting for crossbridge and myofilament lattice structures as well as multicellular myofiber and sheet angle dispersions. Integrating these properties in a finite element model of an actively contracting myocardial tissue slice suggested that these mechanisms may be sufficient to explain the results of biaxial tests in contracted myocardium.