Dynamic stiffness and implications for assisting the operation of the left ventricle

The distribution of bending strain and stiffness in the wall of the left ventricle (LV) is relevant to the augmentation of its function by a modified skeletal-muscle wrap in the new surgical procedure of cardiomyoplasty. A novel approach to ventricular mechanics is presented which blends some finite-element results in engineering with new data available on ventricular geometry. Two simplified axisymmetric strip-element models of the LV are used to illustrate aspects of myocardial stiffness in the bending-strain-energy distribution and the effect on wrap synchronization of a change in cross-fibre stiffness when the heart has nonuniform or ectopic beats. The nonlinear and time-dependent nature of both camping and wall stiffness is derived from differential equations governing the dynamic paths from systole to diastole of finite wall elements around the periphery of an oblique LV slice using magnetic resonance imaging (MRI) data. This leads to a geometric method for determining these parameters. Results for time-dependent stiffnesses of elements in their trajectories are presented for a normal heart.