Toward a Better Understanding of the Etiology of Left Ventricular Dysfunction after Mitral Valve Replacement: An Experimental Study with Possible Clinical Implications

The relative high morbidity and mortality of mitral valve replacement (MVR) appears to be related to an impairment in left ventricular (LV) function. This two-part investigation was designed to assess the effect of MVR on global LV function in an isolated heart preparation and to evaluate whether a mitral prosthesis with a flexible annulus would be of benefit. In part I (14 pigs), the effects of each step in MVR were studied. Division of the chordae tendinae caused a severe deterioration in LV function (systolic pressure, 180 ± 13 versus 120 ± 10 mm Hg; p < 0.05; developed pressure, 167 ± 13 versus 108 ± 11 mm Hg; p < 0.05; first derivative of LV pressure [dP/dt], 2,630 ± 300 versus 1,610 ± 180 mm Hg/sec; p < 0.05; balloon volume, 30 ml). Fixation of the mitral annulus prior to division of the chordae tendineae resulted in a small decrease (no significant) in LV function but had no effect after the chordae tendineae were divided. In Part II (10 pigs), two mitral annular prostheses were studied: a standard rigid prosthesis and a prosthesis of identical size but with a flexible annulus. LV function was better with the flexible than the right prosthesis (systolic presure, 118 ± 10 versus 89 ± 5% control, p < 0.02; developed pressure, 120 ± 11 versus 87 ± 5% control; p < 0.02; dP/dt, 119 ± 10 versus 85 ± 4% control; p < 0.02; balloon volume, 30 ml). These results demonstrate that MVR causes a profound deterioration in LV function, a deterioration primarily due to division of the chordae tendineae. Fixation of the mitral annulus with a rigid prosthesis may also be an important cause of LV dysfunction.