Mitral annular size and shape in sheep with annuloplasty rings

Background: Mitral annuloplasty is an important element of most mitral repa irs, yet the effects of various types of annuloplasty rings on mitral annul ar dynamics are still debated. Recent studies suggest that flexible rings p reserve physiologic mitral annular area change during the cardiac cycle, wh ile rigid rings do not, Methods: To clarify the effects of mitral ring annu loplasty on mitral annular dynamic geometry, we sutured 8 radiopaque marker s equidistantly around the mitral anulus in 3 groups of sheep (n = 7 each: no ring, Carpentier-Edwards semi-rigid Physio-Ring [Baxter Healthcare Corp, Edwards Division. Santa Ana, Calif], and Duran flexible ring [Medtronic, I nc, Minneapolis, Minn]), Ring sizes were selected according to anterior lea flet area and intel-trigonal distance (Physio-Ring 28 mm, n = 7; Duran ring 31 mm, n = 5, and 29 mm, n = 2), After 8 +/- 1 days of recovery, the sheep were sedated and studied by means of biplane videofluoroscopy. Mitral annu lar area was calculated from 3-dimensional marker coordinates without assum ing circular or planar geometry. Results: In the no ring group, mitral annu lar area, varied during the cardiac cycle by 11% +/- 2% (mean +/- SEM; maxi mum = 7.6 +/- 0.2, minimum = 6.8 +/- 0.2 cm(2): P less than or equal to.001 ). Mitral annular area was fixed in the Physio-Ring group (4.6 +/- 0.1 cm(2 )) and, surprisingly, also static in the Duran ring group (4.8 +/- 0.1 cm(2 ); P = .26 vs Physio-Ring), Furthermore, mitral annular 3-dimensional shape changed in the no-ring group during the cardiac cycle, but not in the Phys io-Ring or Duran groups. Conclusions: Mitral annular area and shape did not change during the cardiac cycle after ring annuloplasty, regardless of rin g type. Thus mitral annular area reduction, independent of intrinsic ring f lexibility, is the chief mechanism responsible for the salutary effects of mitral ring annuloplasty.