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 an 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 enddiastolic diameters in the major axis were increased (+ 2%), in the minor axis decreased (- 1%) at any left-ventricular enddiastolic pressure. Systolic shortening of the major axis diameter was considerably reduced (20-27%) at any left-ventricular enddiastolic 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 enddiastolic pressure of 7-8 mmHg no significant changes were present. Peak systolic left-ventricular pressure and heart rate did not change following severance of the chordae tendineae at comparable preload levels, whereas the maximum rate of rise of left-ventricular pressure (dP/dt(max)) (-9 to -10%) as well as left-ventricular stroke volume (-7 to -8%) decreased significantly after destruction of the subvalvular apparatus. These results reveal changes of left-ventricular dimensions and an impairment of left-ventricular performance following mitral valve replacement with excision of the mitral valve leaflets, chordae tendineae, and papillary muscles. These results suggest that preservation of the subvalvular apparatus in mitral valve replacement in patients be seriously considered whenever possible.
