EFFECTS OF PRESERVING MITRAL APPARATUS ON VENTRICULAR SYSTOLIC FUNCTION IN MITRAL-VALVE OPERATIONS IN DOGS

The mitral apparatus can affect left ventricular function through vari ous mechanisms, such as the direct mechanical coupling between the mit ral anulus and papillary muscle and the mitral annular contraction. To evaluate the relative contribution of these mechanisms, we investigat ed in five groups of 35 dogs that underwent open chest operations how preservation of the mitral apparatus affects left ventricular systolic function. We performed atriotomy in the first group. We sutured a pro sthetic rigid ring around the mitral anulus in the second group. We re placed the mitral valve and preserved the anterior chordae in the thir d group, the posterior chordae in the fourth group, and no chordae in the fifth group. The postoperative percentage of recovery of ventricul ar function (as assessed by the slope of the end-systolic pressure-vol ume relation) from preoperative control values were 92.2% +/- 4.8%, 89 .5% +/- 12.8%, 85.7% +/- 9.5%, 75.1% +/- 12.9%, and 61.3% +/- 8.0%, re spectively. Preservation of the mitral apparatus significantly improve d left ventricular function compared with that of conventional mitral valve replacement. The average relative contribution of the ventricula r muscle to left ventricular function, the mitral anulus-papillary mus cle continuity, and the mitral annular contraction were 66.5%, 30.6%, and 2.9%, respectively. We conclude that it is more beneficial to pres erve the mitral apparatus in mitral valve replacement. The prosthetic ring does not detract from the functional benefit of the preservation of the mitral apparatus.