title: Saddle-shaped mitral valve annuloplasty rings experience lower forces compared with flat rings.
abstract: BACKGROUND
  New insight into the 3D dynamic behavior of the mitral valve has prompted a reevaluation of annuloplasty ring designs. Force balance analysis indicates correlation between annulus forces and stresses in leaflets and chords. Improving this stress distribution can intuitively enhance the durability of mitral valve repair. We tested the hypothesis that saddle-shaped annuloplasty rings have superior uniform systolic force distribution compared with a nonuniform force distribution in flat annuloplasty rings.
  
  
  RESULTS
  Sixteen 80-kg pigs had a flat (n=8) or saddle-shaped (n=8) mitral annuloplasty ring implanted. Mitral annulus 3D dynamic geometry was obtained with sonomicrometry before ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat and saddle-shaped annuloplasty rings provided the intraoperative force distribution perpendicular to the annular plane. Average systolic annular height to commissural width ratio before ring implantation was 14.0%+/-1.6%. After flat and saddle shaped ring implantation, the annulus was fixed in the diastolic (9.0%+/-1.0%) and systolic (14.3%+/-1.3%) configuration, respectively (P<0.01). Force accumulation was seen from the anterior (0.72N+/-0.14N) and commissural annular segments (average 1.38N+/-0.27N) of the flat rings. In these segments, the difference between the 2 types of rings was statistically significant (P<0.05). The saddle-shaped annuloplasty rings did not experience forces statistically significantly larger than zero in any annular segments.
  
  
  CONCLUSIONS
  Saddle-shaped annuloplasty rings provide superior uniform annular force distribution compared to flat rings and appear to represent a configuration that minimizes out-of-plane forces that could potentially be transmitted to leaflets and chords. This may have important implications for annuloplasty ring selections.
authors.affiliation: Department of Cardiothoracic & Vascular Surgery, Aarhus University Hospital, Skejby, 8200 Aarhus N, Denmark. morten.jensen@ki.au.dk
authors.forename: Morten O
authors.initials: MO
authors.lastname: Jensen
authors.forename: Henrik
authors.initials: H
authors.lastname: Jensen
authors.forename: Morten
authors.initials: M
authors.lastname: Smerup
authors.forename: Robert A
authors.initials: RA
authors.lastname: Levine
authors.forename: Ajit P
authors.initials: AP
authors.lastname: Yoganathan
authors.forename: Hans
authors.initials: H
authors.lastname: Nygaard
authors.forename: J Michael
authors.initials: JM
authors.lastname: Hasenkam
authors.forename: Sten L
authors.initials: SL
authors.lastname: Nielsen
mesh_terms: D000818:Animals; D003326:Coronary Circulation; D003971:Diastole; D004867:Equipment Design; D006439:Hemodynamics; D008943:Mitral Valve / Q000601:surgery*; D011184:Postoperative Period; D019736:Prostheses and Implants / Q000592:standards; D013314:Stress, Mechanical; D013552:Swine; D013599:Systole; D016277:Ventricular Function, Left