Effects of preserving mitral apparatus on ventricular systolic function in mitral valve operations in dogs

The mitral apparatus can affect left ventricular function through various mechanisms, such as the direct mechanical coupling between the mitral anulus and papillary muscle and the mitral annular contraction. To evaluate the relative contribution of these mechanisms, we investigated 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 prosthetic rigid ring around the mitral anulus in the second group. We replaced the mitral valve and preserved the anterior chordae in the third group, the posterior chordae in the fourth group, and no chordae in the fifth group. The postoperative percentage of recovery of ventricular function (as assessed by the slope of the end-systolic pressure-volume 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%, respectively. Preservation of the mitral apparatus significantly improved left ventricular function compared with that of conventional mitral valve replacement. The average relative contribution of the ventricular muscle to left ventricular function, the mitral anulus-papillary muscle continuity, and the mitral annular contraction were 66.5%, 30.6%, and 2.9%, respectively. We conclude that it is more beneficial to preserve the mitral apparatus in mitral valve replacement. The prosthetic ring does not detract from the functional benefit of the preservation of the mitral apparatus.