Annular height-to-commissural width ratio of annulolasty rings in vivo

A "saddle-shaped" mitral annulus with an optimal ratio between annular height and commissural diameter may reduce leaflet and chordal stress and is purported to be conserved across mammalian species. Whether annuloplasty rings maintain this relationship is unknown.

Twenty-three adult sheep underwent implantation of radiopaque markers on the left ventricle and mitral annulus. Eight animals underwent implantation of a Carpentier-Edwards Physio ring, 7 underwent a Medtronic Duran flexible ring, and 8 served as controls. Animals were studied with biplane videofluoroscopy 7 to 10 days postoperatively. Annular height and commissural width (CW) were determined from 3D marker coordinates, and annular height:CW ratio (AHWCR) was calculated. Annular height was similar in Control and Duran animals but significantly lower in the Physio group at end diastole (8.4+/-3.8, 6.7+/-2.3, and 3.4+/-0.6 mm, respectively, for Control, Duran, and Physio; ANOVA=0.005) and at end systole (14.5+/-6.2, 10.5+/-5.5, and 5.8+/-2.5 mm, respectively, for Control, Duran, and Physio; ANOVA=0.004). Both ring groups reduced CW significantly relative to Control. AHCWR did not differ between Control and Duran but was lower in Physio (23+/-11%, 24+/-7%, and 12+/-2% at end diastole and 42+/-17%, 37+/-17%, and 21+/-10% at end systole, respectively, for Control, Duran, and Physio, respectively; ANOVA <0.05 for both).

Mitral annular height and AHWCR of the native valve were unchanged by a Duran ring, whereas the Physio ring led to a lower AHWCR. Theoretically, such a flexible annuloplasty ring may provide better leaflet stress distribution by maintaining normal AHWCR.