title: Saddle-shaped mitral valve annuloplasty rings improve leaflet coaptation geometry.
abstract: OBJECTIVE
  The mitral valve annulus naturally conforms to a saddle shape in systole. This configuration is believed to put the leaflets into a lower-energy equilibrium with the annulus and subvalvular apparatus. Conventional flat annuloplasty rings restrict posterior leaflet motion, which may result in a "monocusp" valve, affecting valvular stress distribution. It is hypothesized that saddle-shaped annuloplasty rings cause less distortion of the physiologic leaflet geometry than do flat rings.
  
  
  METHODS
  Twelve pigs were studied in an acute setting with 3-dimensional echocardiography and sonomicrometry before and after implantation of rigid flat (n = 5) and saddle-shaped (n = 7) annuloplasty rings. The rings were true sized to the annulus with equal anterior-posterior and commissure-commissure circumferential dimensions. The saddle-shaped rings had an annular height to commissural width ratio of 15%.
  
  
  RESULTS
  Saddle-shaped rings maintained both leaflets operational (P < .01). Flat rings made the posterior leaflet immobile and the anterior leaflet aligned flat along the annulus in systole, effectively resulting in monoleaflet function. The average distance from the papillary muscle tips to the posterior annulus decreased by 2.4 ± 0.4 mm after flat ring implantation (P < .01).
  
  
  CONCLUSIONS
  Saddle-shaped annuloplasty rings provide better leaflet coaptation geometry than do flat rings by not hoisting the papillary muscles toward the posterior annulus through the commissural chordae, allowing greater leaflet mobility. This entails a potentially beneficial impact on valvular stress distribution that could affect durability of the repaired valve.
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, Institute of Clinical Medicine, Aarhus University Hospital, Skejby, Aarhus, Denmark. dr.morten.jensen@gmail.com
authors.forename: Morten O
authors.initials: MO
authors.lastname: Jensen
authors.forename: Henrik
authors.initials: H
authors.lastname: Jensen
authors.forename: Robert A
authors.initials: RA
authors.lastname: Levine
authors.forename: Ajit P
authors.initials: AP
authors.lastname: Yoganathan
authors.forename: Niels Trolle
authors.initials: NT
authors.lastname: Andersen
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; D001696:Biomechanical Phenomena; D019560:Echocardiography, Three-Dimensional; D006350:Heart Valve Prosthesis; D019918:Heart Valve Prosthesis Implantation; D008943:Mitral Valve / Q000503:physiopathology*; D058386:Mitral Valve Annuloplasty / Q000295:instrumentation / Q000379:methods*; D008955:Models, Cardiovascular; D011474:Prosthesis Design; D013314:Stress, Mechanical; D013552:Swine