Preservation versus severance of the subvalvular apparatus in mitral valve replacement: an experimental study

Preservation of the subvalvular apparatus in mitral valve replacement has been suggested to improve postoperative left ventricular performance. As it is difficult to quantify the change in left ventricular performance clinically, an experimental model was devised to demonstrate the contribution of the subvalvular apparatus to left ventricular function. In eight dogs mitral valve replacement (St. Jude prostheses) was performed, preserving the subvalvular apparatus by plicating the leaflets with the prosthesis on the mitral annulus. Left ventricular function was assessed during volume loading with blood before and after cutting the chordae tendineae by means of electrocautery applied via flexible wires slung around the chordae and exteriorized through the left ventricular wall. Left ventricular internal diameters were measured by sonomicrometry. End-diastolic volume (LVedV) and stroke volume were determined by dye dilution and left ventricular pressure (LVP) by cathter tip manometer. The results showed that after cutting the chordae the heart rate did not differ from the pre-cut values at any LVedP. The peak left ventricular pressure was only significantly reduced at an LVedP of 5 mmHg and minor axis diameters were only increased at an LVedP of 9-12 mmHg. Significant changes were observed, however, in LV dP/dtmax (= maximum rise of LVP) (-15%), major axis end-diastolic diameter (+10%) and systolic shortening (-40%), end-diastolic volume (+18%) and ejection fraction (-16%) at any LVedP, and stroke volume (-24%) at any LVedV.(ABSTRACT TRUNCATED AT 250 WORDS)