title: What forces act on a flat rigid mitral annuloplasty ring?
abstract: OBJECTIVE
  Increasing mitral valve repair durability requires successful restoration and support with annuloplasty rings. The stress distribution in these devices indirectly determines the success of the repair. It is hypothesized that changes in annular geometry throughout the cardiac cycle result in adverse strain distribution in stiff, flat annuloplasty rings, and hence non-physiological loading of the myocardium. The study aim was to identify the three-dimensional (3-D) force distribution in mitral annuloplasty rings.
  
  
  METHODS
  Eight animals were included in an acute porcine study. The mitral annulus 3-D dynamic geometry was assessed with sonomicrometry prior to ring insertion. Strain gauges mounted on dedicated D-shaped rigid flat annuloplasty rings enabled dynamic force measurements to be made perpendicular to the annulus plane.
  
  
  RESULTS
  The average systolic annular height to commissural width ratio before ring implantation was 13.7 +/- 1.4%. Following ring implantation, the annulus was fixed in the diastolic flat configuration (p <0.01). Force accumulation was seen from the anterior (0.7 +/- 0.4 N) and commissural (1.4 +/- 1.0 N) annular segments; both forces were acting in opposite directions and were statistically significantly larger than zero (p <0.01; n = 8).
  
  
  CONCLUSIONS
  These data demonstrate highest strains at the anterior and commissural areas of flat mitral annuloplasty rings, and support the hypothesis that the mitral valve annulus and its attached valvular and subvalvular structures apply systolic torque onto the flat annuloplasty ring in an attempt to conform it into the saddle-shaped configuration.
authors.affiliation: Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, Skejby, Aarhus N, Denmark. morten.jensen@ki.au.dk
authors.forename: Morten Ø
authors.initials: MØ
authors.lastname: Jensen
authors.forename: Henrik
authors.initials: H
authors.lastname: Jensen
authors.forename: Sten L
authors.initials: SL
authors.lastname: Nielsen
authors.forename: Morten
authors.initials: M
authors.lastname: Smerup
authors.forename: Peter
authors.initials: P
authors.lastname: Johansen
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
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006350:Heart Valve Prosthesis; D008943:Mitral Valve / Q000502:physiology* / Q000601:surgery*; D023421:Models, Animal; D008955:Models, Cardiovascular; D013314:Stress, Mechanical; D013552:Swine; D019415:Torque