Evaluation of left ventricular function based on simulated systolic flow dynamics computed from regional wall motion

Abstract

Left ventricular (LV) chamber flow is undoubtedly influenced by the time-dependent regional motion of the LV wall. In an attempt to obtain diagnostic parameters based on LV chamber flow, we computed the LV chamber, two-dimensional systolic velocity and pressure distribution for two right anterior oblique (RAO) ventriculograms: one normal, one with ischemic coronary artery disease, and several simulations with prescribed abnormal wall motion. The flow fields are obtained by solving the discretized two-dimensional Navier-Stokes equations for viscous, incompressible unsteady flow using the finite analytic method. These solutions were used as a basis for two LV assessment parameters: (1) local pressure gradient near the LV wall, and (2) the central ejection region (CER), defined as the region of flow domain in which the obtained velocity field vectors are aligned ±5° from the LV long axis. A CER coefficient, R, derived from the location and orientation of the CER within the LV cavity, is defined such that R=0 for a heart which produces no CER, and R=1 for a heart whose contraction is perfectly even along the entire RAO LV outline. The computed local pressure gradients in the ischemic heart near the apical wall region were reduced compared with those computed in the normal heart. An observable decrease in magnitude of the pressure gradients in the apical region for increasing severity of abnormal wall motion was also indicated. However, the prescribed abnormal wall motion simulations generated reduced pressure gradients in regions of abnormal wall motion and normal regions as well. Therefore, the local wall pressure gradient may not be suitable for localization of coronary occlusion but for presence of disease only. The time-averaged CER coefficient was 0.709 for the normal heart and 0.453 for the diseased heart. The CER shifted toward the region of LV wall which exhibits the abnormal motion, and the CER coefficient decreased with increasing severity of abnormal wall motion. The CER coefficient provides a qualitative and quantitative measure of global function that regional wall motion analysis cannot provide, and is a parameter which is sensitive to regional and temporal abnormalities and the resulting compensatory actions which cannot be detected by global parameters.