Importance of the left ventricular subvalvular apparatus for cardiac performance

The importance of the subvalvular mitral apparatus for left ventricular performance was studied in eight anesthetized dogs. During extracorporeal circulation St. Jude Medical mitral valve prostheses were implanted preserving the chordae tendineae. Flexible wires were slung around the chordae tendineae and brought to the outside through the left ventricular wall to cut the chordae tendineae by electrocautery in the closed beating heart. The left ventricular diameters were measured by sonomicrometry, left ventricular stroke volume and enddiastolic volume by dye dilution, and left ventricular pressure by catheter tip manometer. Data were collected at different preloads achieved by volume loading with blood before and after the chordae tendineae were cut. The results showed that after the chordae tendineae had been cut left ventricular systolic pressure, heart rate, diastolic and systolic diameters of the left ventricle along the minor axis were not different from the pre-cut values at any left ventricular enddiastolic pressure. However, significant differences were observed for maximum dp/dt (-15%), major axis diastolic diameter (+10%) and systolic shortening (-40%), enddiastolic volume (+18%) at any left ventricular enddiastolic pressure, and stroke volume (-24%) at any enddiastolic volume level. The data demonstrate that the subvalvular apparatus not only maintains physiologic valve function, but contributes significantly to left ventricular performance. The impairment of left ventricular function following removal of the subvalvular apparatus might be aggravated in pre-injured hearts in mitral valve disease. Consequently, the subvalvular apparatus should be preserved in mitral valve replacement whenever possible.