The Study on the Pathogenesis of Mitral Valve Prolapse in Patients with Straight Back Syndrome and Those with Idiopathic Mitral Valve Prolapse by Two-dimensional Echocardiography

In order to investigate the pathogenetic difference of mitral valve prolapse between patients with idiopathic mitral valve prolapse (MVP) and those with straight back syndrome (SBS), two-dimensional echocardiographic analysis was performed in 8 age matched patients with MVP, 13 patients with SBS and 9 normal subjects. All echocardiographic images were recorded by a 3/4 inch video tape recorder. From these video tape recording images, the endocardial surface of the left ventricle, the mitral commissures and the papillary muscles in the short axis view were traced every 3 frames from R wave to the end of T wave of the electrocardiogram. The atrial surface of the mitral leaflets on the longitudinal axis view was also traced. Furthermore, the lesion of prolapse was examined from the medial to the lateral side in patients with MVP and those with SBS by scanning of the longitudinal axis view. Pulsed Doppler echocardiographic study was also performed in all subjects to investigate the mitral and tricuspid regurgitation. In all cases, cardio-thoracic ratio (CTR) and the ratio of anteroposterior diameter and transverse diameter of the thorax (APDT/TDT) were calculated from the chest roentgenogram. Prolapsed distance (P. D.), ellipsoidal index (E. I.), distance from the gravity point to each mitral commissure (ML, MM) and that from the gravity point to each midpoint of the papillary muscle (PL, PM) were measured from those tracing images. Displacement index of the mitral apparatus (D. I.) was calculated as (ML/PL)/ (MM/PM). CTR was larger in the MVP group and APDT/TDT was smaller in SBS than those in other groups. Characteristic echocardiographic manifestations were observed in all patients with SBS. The anterior mitral leaflet was prolapsed across the posterior one and the lesion of prolapse was located in the centromedial portion. Ellipsoidal left ventricle was observed from end-diastole to mid-systole at the mitral valve and the papillary muscle levels in SBS, but not in MVP and normal control groups. Left ventricular wall motion was characteristic in patients with SBS. Hypokinesis-like wall motion was found from the intraventricular septum to the inferior wall. The postero-medial papillary muscle moved for anterior direction, and the antero-lateral papillary muscle for horizontal direction. On the other hand, synchronous wall motion and papillary muscle movement were observed in the other 2 groups. A significant positive correlation was demonstrated between P. D. and D. I. values in SBS group, while no relationship was found between 2 parameters in patients with MVP. Mitral regurgitation was detected in all patients with MVP. Three patients had severe regurgitation, while the other patients had mild to moderate regurgitation. Mild tricuspid regurgitation was demonstratedin 4 patients with MVP. In patients with SBS, only 4 out of 13 cases showed a mild mitral regurgitation. From these results, it was suggested that mitral valve prolapse in patients with SBS was produced by an abnormal movement of the mitral apparatus due to ellipsoidal left ventricle, and that the mechanism of mitral valve prolapse in patients with SBS may be different from that of patients with MVP