Three-dimensional geometric comparison of partial and complete flexible mitral annuloplasty rings

Background: It has previously been shown in sheep that mitral annular physiologic dynamics during the cardiac cycle are abolished by complete ring annuloplasty, but recent clinical studies suggest that flexible partial ring annuloplasty preserves normal mitral annular dynamics. Methods: Eight radiopaque markers were sutured equidistantly around the mitral anulus in 3 groups of sheep: no-ring control animals (n = 16); animals with a flexible Tailor partial ring annuloplasty (n = 6; St Jude Medical, Inc, St Paul, Minn); and animals with a flexible Duran ring annuloplasty (n = 7; Medtronic, Inc, Minneapolis, Minn). After 7 to 110 days' recovery, 3-dimensional marker coordinates were measured by biplane cinefluoroscopy. Mitral annular area and folding (defined as displacement of the mitral anulus from a least-squares plane) and mitral annular septal-lateral and commissure-commissure dimensions were calculated from the 3-dimensional marker coordinates throughout the cardiac cycle every 17 ms. Results: In the no-ring control group mitral annular area varied from 8.0 +/- 0.2 to 7.2 +/- 0.2 cm(2) (10% +/- 2%), and the septal-lateral and commissure-commissure dimensions varied from 27.7 +/- 0.4 to 25.9 +/- 0.4 mm (7% +/- 1%) and from 38.2 +/- 0.8 to 36.4 +/- 0.8 mm (5% +/- 1%), respectively (mean standard error of the mean, P <.001 for all comparisons). In the Duran ring annuloplasty and Tailor partial ring annuloplasty groups, the anulus was fixed in size throughout the cardiac cycle (area = 4.8 +/- 0.1 and 5.3 +/- 0.3 cm(2), septal-lateral = 21.8 +/- 0.7 and 22.0 +/- 0.8 nun, and commissure-commissure = 27.7 +/- 0.7 and 31.2 +/- 1.7 mm). Mitral annular folding did not differ significantly between the control and Tailor partial ring annuloplasty groups but was dampened in the Duran ring annuloplasty group. Conclusions: Partial Tailor flexible ring annuloplasty fixed mitral annular area and dimensions throughout the cardiac cycle in sheep; however, it preserved physiologic mitral annular folding dynamics, which might be important in terms of long-term valve function and prevention of left ventricular outflow tract obstruction.