Significance of the subvalvular apparatus for left-ventricular dimensions and systolic function: experimental replacement of the mitral valve.

To study the significance of the subvalvular apparatus for left-ventricular performance in mitral valve replacement, a new experimental model was developed. In 21 dogs St. Jude prostheses were implanted in the mitral position preserving the chordae tendineae and the papillary muscles by plicating and fixing the mitral leaflets with the prosthesis on the valvular annulus. Flexible steel wires were slung around the chordae tendineae of the anterior and the posterior papillary muscle separately and passed through the left ventricular wall via insulating plastic cannulas. Left-ventricular dimensions and global systolic function were measured during volume loading with blood before and after severance of the chordae tendineae by external application of electrocautery to the steel wires. Thus the heart continued beating without any interference following loss of the subvalvular apparatus. The external left ventricular diameters in the major and minor axis were determined by sonomicrometry. Left-ventricular systolic and diastolic pressures were measured by catheter tip manometers, stroke volume by electromagnetic measurements of flow in the ascending aorta. When the chordae tendineae had been cut, left-ventricular end-diastolic diameters in the major axis were increased ( + 2%), in the minor axis decreased (-1%) at any left-ventricular end-diastolic pressure. Systolic shortening of the major axis diameter was considerably reduced (20-27%) at any left-ventricular end-diastolic pressure following severance of the chordae tendineae. Significant increase of the systolic shortening in the minor axis diameter occurred at preload levels of 3-6 mmHg (15-8%), while at higher left-ventricular end-diastolic pressure of 7-8 mmHg no significant changes were present.(ABSTRACT TRUNCATED AT 250 WORDS)