Analysis of wall dynamics and directional components of left ventricular contraction in man

Abstract

The extent and rate of left ventricular wall thickening during systole has previously been shown to be a useful measure of regional ventricular function and to play an important role in the ejection of blood from the left ventricle. The relation among systolic wall thickening, the directional components of contraction, ejection fraction and force velocity measurements is therefore of interest in understanding the dynamics of contraction of the intact ventricle. This report describes a theoretical basis and method for using ventricular angiograms to quantify the separate contributions of longitudinal shortening, circumferential shortening and systolic wall thickening to overall ventricular performance in man. One hundred twenty-two patients with valvular, coronary or myocardial heart disease were studied with biplane angiocardiography during diagnostic cardiac catheterizations. The percent contribution of directional components to total work or power developed by a mid-wall equatorial element of myocardium was shown to be: longitudinal, 14 percent in normal and diseased ventricles; circumferential, 45 percent in normal, increasing to 55 percent in dilated ventricles (P less than 0.005); wall thickening, 40 percent in normal, decreasing to 31 percent in dilated ventricles (P less than 0.001). Thus, left ventricular contraction, which is expressed as systolic wall thickening, quantified separately from inward wall displacement due to mid-wall circumferential shortening, accounts for nearly half of segmental left ventricular work and power. The rate and extent of ventricular wall thickening correlated closely with ejection fraction (r = 0.92 and 0.95, respectively) and with velocity of circumferential shortening (r = 0.90 and 0.80, respectively). Previous models of ventricular and myocardial mechanics that include computations of mid-wall longitudinal and circumferential stress and strain do not appear to account for the large contribution of systolic wall thickening to the performance of the intact heart. Force-velocity relations as heretofore described may therefore be partial descriptors of myocardial function in the intact ventricle.