title: Mitral annular hinge motion contribution to changes in mitral septal-lateral dimension and annular area.
abstract: OBJECTIVE
  The mitral annulus is a dynamic, saddle-shaped structure consisting of fibrous and muscular regions. Normal physiologic mechanisms of annular motion are incompletely understood, and more complete characterization is needed to provide rational basis for annuloplasty ring design and to enhance clinical outcomes.
  
  
  METHODS
  Seventeen sheep had radiopaque markers implanted; 16 around the annulus and 2 on middle anterior and posterior leaflet edges. Four-dimensional marker coordinates were acquired with biplanar videofluoroscopy at 60 Hz. Hinge angle was quantified between fibrous and muscular annular planes, with 0 degrees defined at end diastole, to characterize its contribution to alterations in mitral septal-lateral dimension and 2-dimensional total annular area throughout the cardiac cycle.
  
  
  RESULTS
  During isovolumic contraction (pre-ejection), hinge angle abruptly increased, reaching maximum (steepest saddle shape, change 18 degrees +/- 13 degrees ) at peak left ventricular pressure. During ejection, hinge angle did not change; it then decreased during early filling (change 2 degrees +/- 2 degrees ). Septal-lateral dimension and total area paralleled hinge angle dynamics and leaflet distance (anterior to posterior marker). Pre-ejection septal-lateral reduction was 13% +/- 7% (3.3 +/- 1.5 mm) from 9% muscular dimension fall and 18 degrees +/- 13 degrees hinge angle increase.
  
  
  CONCLUSIONS
  Pre-ejection increase in hinge angle contributes substantially to septal-lateral and total area reduction, facilitating leaflet coaptation. Semirigid annuloplasty rings or partial bands may preserve hinge motion, but possible recurrent annular dilatation could result in recurrent mitral regurgitation. Long-term clinical studies are required to determine who might benefit most from preserving intrinsic hinge motion without compromising repair durability.
authors.affiliation: Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Akinobu
authors.initials: A
authors.lastname: Itoh
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Ennis
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Bothe
authors.forename: Julia C
authors.initials: JC
authors.lastname: Swanson
authors.forename: Gaurav
authors.initials: G
authors.lastname: Krishnamurthy
authors.forename: Tom C
authors.initials: TC
authors.lastname: Nguyen
authors.forename: Neil B
authors.initials: NB
authors.lastname: Ingels
authors.forename: D Craig
authors.initials: DC
authors.lastname: Miller
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D006348:Cardiac Surgical Procedures; D005471:Fluoroscopy; D006439:Hemodynamics; D021621:Imaging, Three-Dimensional; D008297:Male; D008943:Mitral Valve / Q000000981:diagnostic imaging / Q000502:physiology* / Q000601:surgery*; D023421:Models, Animal; D034561:Sheep, Domestic; D013635:Tantalum
chemical_list: D013635:Tantalum