title: In vitro characterization of the mechanisms responsible for functional tricuspid regurgitation.
abstract: BACKGROUND
  Functional tricuspid regurgitation (TR) is increasingly recognized as a source of morbidity. Current repair strategies focus on annular remodeling because annular dilatation is common in patients with TR. Although papillary muscle (PM) displacement is recognized in functional mitral regurgitation, its role in TR is less well characterized. The objective of this in vitro study was to further clarify the mechanisms by which TR occurs as an effect of annular dilatation and PM displacement.
  
  
  RESULTS
  Porcine tricuspid valves (n=16) were studied in an in vitro right heart simulator. The valve dynamics were quantified with isolated annular dilatation starting with a normal annular size (6 cm(2)) and incrementally dilated up to 100%, isolated PM displacement, and a combination of the 2. All valves lost competence at 40% dilatation, resulting in a TR of 7.9 ± 3.4 mL (P ≤ 0.05) compared with baseline and central residual leaflet length of 0.5 ± 0.2 cm. Multidirectional displacement of the anterior and posterior/septal PMs and all PMs significantly (P ≤ 0.05) increased TR, with normal annular area. Malcoaptation was observed where the 3 leaflets joined with all significant levels of TR. The anterior leaflet had the greatest percent change in residual leaflet length, whereas PM displacement caused a reduction in residual leaflet length for the septal leaflet for all conditions.
  
  
  CONCLUSIONS
  This study shows that although annular dilatation alone leads to TR, isolated PM displacement can also cause TR; annular remodeling strategies should be tailored in the setting of severe PM displacement.
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Spinner
authors.forename: Patrick
authors.initials: P
authors.lastname: Shannon
authors.forename: Dana
authors.initials: D
authors.lastname: Buice
authors.forename: Jorge H
authors.initials: JH
authors.lastname: Jimenez
authors.forename: Emir
authors.initials: E
authors.lastname: Veledar
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Del Nido
authors.forename: David H
authors.initials: DH
authors.lastname: Adams
authors.forename: Ajit P
authors.initials: AP
authors.lastname: Yoganathan
mesh_terms: D000818:Animals; D004867:Equipment Design; D006439:Hemodynamics / Q000502:physiology; D066298:In Vitro Techniques; D008953:Models, Anatomic; D010210:Papillary Muscles / Q000503:physiopathology; D011673:Pulsatile Flow / Q000502:physiology*; D013552:Swine; D014261:Tricuspid Valve / Q000503:physiopathology*; D014262:Tricuspid Valve Insufficiency / Q000209:etiology* / Q000503:physiopathology*