title: Effect of annular shape on leaflet curvature in reducing mitral leaflet stress.
abstract: BACKGROUND
  Leaflet curvature is known to reduce mechanical stress. There are 2 major components that contribute to this curvature. Leaflet billowing introduces the most obvious form of leaflet curvature. The saddle shape of the mitral annulus imparts a more subtle form of leaflet curvature. This study explores the relative contributions of leaflet billowing and annular shape on leaflet curvature and stress distribution.
  
  
  RESULTS
  Both numerical simulation and experimental data were used. The simulation consisted of an array of numerically generated mitral annular phantoms encompassing flat to markedly saddle-shaped annular heights. Highest peak leaflet stresses occurred for the flat annulus. As saddle height increased, peak stresses decreased. The minimum peak leaflet stress occurred at an annular height to commissural width ratio of 15% to 25%. The second phase involved data acquisition for the annulus from 3 humans by 3D echocardiography, 3 sheep by sonomicrometry array localization, 2 sheep by 3D echocardiography, and 2 baboons by 3D echocardiography. All 3 species imaged had annuli of a similar shape, with an annular height to commissural width ratio of 10% to 15%.
  
  
  CONCLUSIONS
  The saddle shape of the mitral annulus confers a mechanical advantage to the leaflets by adding curvature. This may be valuable when leaflet curvature becomes reduced due to diminished leaflet billowing caused by annular dilatation. The fact that the saddle shape is conserved across mammalian species provides indirect evidence of the advantages it confers. This analysis of mitral annular contour may prove applicable in developing the next generation of mitral annular prostheses.
authors.affiliation: Philips Medical Systems, Andover, Mass, USA. ivan_salgo@attbi.com
authors.forename: Ivan S
authors.initials: IS
authors.lastname: Salgo
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Gorman
authors.forename: Robert C
authors.initials: RC
authors.lastname: Gorman
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Jackson
authors.forename: Frank W
authors.initials: FW
authors.lastname: Bowen
authors.forename: Theodore
authors.initials: T
authors.lastname: Plappert
authors.forename: Martin G
authors.initials: MG
authors.lastname: St John Sutton
authors.forename: L Henry
authors.initials: LH
authors.lastname: Edmunds
mesh_terms: D000818:Animals; D019560:Echocardiography, Three-Dimensional; D020342:Finite Element Analysis; D006801:Humans; D008943:Mitral Valve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008955:Models, Cardiovascular; D010215:Papio; D012756:Sheep; D013314:Stress, Mechanical