Two-Dimensional Echocardiographic Analysis of the Dynamic Geometry of the Left Ventricle: The Basis for an Improved Model of Wall Motion

Abstract

To establish an appropriate echocardiographic model for wall motion analysis we first determined the precise dynamic geometry of the left ventricle during systole, as visualized by two-dimensional echocardiography. With the epicardial apex and the aortic-ventricular and mitral-ventricular junctions as anatomic landmarks, we quantitatively analyzed apical long-axis views in 61 normal subjects, 41 patients with anterior myocardial infarction, and nine patients with posterior myocardial infarction. Thoracic impedance registration allowed exclusion of extracardiac motion from the measurements. In normal subjects the epicardial apex moved outwardly only 0.6 +/- 0.3 mm (mean +/- standard error). Examination of 15 hearts fixed in formalin revealed apical myocardial thickness of 1.5 +/- 0.2 mm. These data suggest that the observed inward motion of the endocardial apex (4.1 +/- 0.7 mm) resulted from obliteration of the apical cavity as a result of inward motion of the adjacent walls. Translation of the base was considerable in normal subjects (14.1 +/- 0.4 mm) and decreased in myocardial infarction (9.1 +/- 0.5 mm, p less than 0.0001). Unequal shortening of the adjacent walls in anterior and posterior myocardial infarction caused basal rotation in the opposite direction (-9.1 +/- 0.8 degrees and 9.7 +/- 1.4 degrees, respectively, p less than 0.0001 versus that of normal subjects, -3.4 +/- 0.7 degrees). Long-axis rotation was not clinically significant (less than 1 degree). We conclude that during ventricular contraction the apex serves as a stable point, whereas the base translates toward the apex because of shortening of the adjacent walls. We then propose a model for analyzing regional wall motion from two-dimensional echocardiograms on the basis of these observations.