Rigid ring fixation of the mitral annulus does not impair left ventricular systolic function in the normal canine heart.

BACKGROUND

Previous studies suggest that rigid fixation of the mitral annulus with an annuloplasty ring may impair left ventricular (LV) systolic performance. We used load-insensitive indexes of global and regional LV contractile mechanics to test the hypothesis that rigid fixation of the mitral annulus alters LV systolic function.

METHODS AND RESULTS

Global and regional LV systolic mechanics were compared in 10 dogs during two mitral annular conditions: rigidly fixed and freely mobile. Carpentier-Edwards annuloplasty rings (20-24 mm) were inserted using a special buttressing suture technique that permitted alternate cinching of the ring down onto the annulus and subsequent removal away from the annulus. Aortic flow was measured with an electromagnetic flow probe, LV pressure by a micromanometer, and LV wall thickness and three near-orthogonal LV endocardial chamber dimensions using piezoelectric crystals during four sequential ring conditions: 1) down, 2) away, 3) down, and 4) away. The following parameters were analyzed during each ring condition to assess global LV systolic function: end-systolic chamber elastance (end-systolic pressure-volume relation), fiber elastance (end-systolic stress-volume relation), preload recruitable stroke work, and myocardial stress-strain relation. Additionally, regional LV systolic performance was assessed using the end-systolic pressure-diameter relation and a regional analog of preload recruitable stroke work. No significant differences in any of these measurements of LV systolic mechanics were observed between the two mitral annular conditions.

CONCLUSIONS

Rigid fixation of the mitral annulus alters neither global nor regional LV systolic function in anesthetized, open-chest dogs with normal ventricles.