Echocardiographic study of abnormal position and motion of the posterobasal wall of the left ventricle in cases of giant left atrium.

In 35 of 70 patients with rheumatic mitral valve disease, two dimensional echocardiography revealed the posterobasal wall of the left ventricle to be entrapped between the left ventricular and atrial cavities and bent inward. The motion of the bending segment was paradoxical. This abnormality was assumed to be induced by the left atrial dilatation extending inferiorly behind the left ventricle, because the length of the bending segment correlation with the left atrial dimension. There was no correlation between the degree of abnormal bending and left atrial pressure, mitral valve pressure gradient or left ventricular dimension. The systolic excursion of the posterobasal wall of the left ventricle was reduced according to the length of the bending segment. This abnormal feature was also observed in five postmortem heart specimens with an extremely dilated left atrium. The macroscopic and microscopic findings in the myocardium of the bending segment were not different from those of the remaining segment of the left ventricle. Therefore, the asynergic motion of the bending segment is assumed to be caused by the abnormal spatial orientation of the left ventricle and the left atrium. It should be considered that the giant left atrium not only oppresses the surrounding organs but also affects the left ventricle.