DYNAMIC STIFFNESS AND IMPLICATIONS FOR ASSISTING THE OPERATION OF THELEFT-VENTRICLE

The distribution of bending strain and stiffness in the wall of the le ft ventricle (LV) is relevant to the augmentation of its function by a modified skeletal-muscle wrap in the new surgical procedure of cardio myoplasty. A novel approach to ventricular mechanics is presented whic h blends some finite-element results in engineering with new data avai lable on ventricular geometry. Two simplified axisymmetric strip-eleme nt models of the LV are used to illustrate aspects of myocardial stiff ness in the bending-strain-energy distribution and the effect on wrap synchronization of a change in cross-fibre stiffness when the heart ha s nonuniform or ectopic beats. The nonlinear and time-dependent nature of both damping and wall stiffness is derived from differential equat ions governing the dynamic paths from systole to diastole of finite wa ll elements around the periphery of an oblique LV slice using magnetic resonance imaging (MRI) data. This leads to a geometric method for de termining these parameters. Results for time-dependent stiffnesses of elements in their trajectories are presented for a normal heart.