Papillary muscles contraction does not change ventricular wall mechanics

Papillary muscles play a crucial role to support valves in the ventricles. However, much less is known about the role in ventricular wall mechanics. Evidence in the literature is inconclusive, showing both of changes in wall strain and indications of no changes in strain after detachment of papillary muscles. We designed a high-resolution 3D model of canine ventricles to investigate the effects of papillary muscles on strain in the regions overlying papillary muscles. An anatomical model was obtained from in-vitro MRI and a realistic fiber geometry assuming transmural rotation in the ventricular wall. Boundary conditions were either: 1) the attached state in which movements of the papillary muscle tips were restricted to the plane parallel to the base of the ventricles; or 2) the detached state where no constraints were placed on the muscle tips. Strains were measured at locations overlying anterior papillary muscle and compared between attached and detached papillary muscle states. In simulation of typical physiological contractions, we found essentially identical pattern in all strain components in the two cases with minor changes near the anterior papillary muscle. Further studies will be required to generalize the results to more anatomical reconstructions and a wider range of conditions.