title: Mechanisms of atrial mitral regurgitation: insights using 3D transoesophageal echo.
abstract: OBJECTIVE
  Functional mitral regurgitation (FMR) is a consequence of mitral annular enlargement, leaflet tethering and reduced co-aptation. The importance of the left atrium (LA) as a cause of mitral regurgitation (MR) is less clear. We applied a co-aptation index using three-dimensional (3D) transoesophageal echocardiography to FMR and MR secondary to LA dilatation (atrial mitral regurgitation, AMR).
  
  
  RESULTS
  Seventy-two patients underwent comprehensive 3D echo studies: FMR (n = 19); AMR (n = 33); and 20 controls. We recorded: LV size and function; LA dimensions; mitral annular area (MVA); and leaflet area in early and late systole. MVA fractional change was defined: (MVA late systole - MVA early systole)/MVA late systole × 100%; the co-aptation index was defined: (leaflet area early systole - leaflet area late systole)/leaflet area early systole × 100%. Despite normal LV size and function in AMR, MVA was increased similarly to FMR (AMR 12.86 cm(2) vs. FMR 12.33 cm(2), P = ns; both P < 0.01 vs. controls 8.83 cm(2)), and MVA fractional change similarly reduced (AMR 5.1% vs. FMR 6.3%; P = ns; both P < 0.001 vs. controls 14.6%). The co-aptation index was reduced in both MR groups (FMR 6.6% vs. AMR 7.0%, P = ns; both P < 0.001 vs. controls 19.6%). After multivariate analysis, the co-aptation index (χ(2) = 41.2) and MVA fractional change (χ(2) = 22.1) remained the strongest predictors of MR (both P < 0.001 for the model). A co-aptation index of ≤13% was 96% sensitive and 90% specific for the presence of MR.
  
  
  CONCLUSIONS
  LA dilatation leads to MVA enlargement, reduced leaflet co-aptation and MR even without LV dilatation. A co-aptation index describes this in vivo. This work provides insights into the mechanism of AMR.
authors.affiliation: Department of Medicine, University of Cambridge, Addenbrookes Hospital, Hills Road, Cambridge CB2 0QQ, UK.
authors.forename: Liam
authors.initials: L
authors.lastname: Ring
authors.forename: David P
authors.initials: DP
authors.lastname: Dutka
authors.forename: Francis C
authors.initials: FC
authors.lastname: Wells
authors.forename: Simon P
authors.initials: SP
authors.lastname: Fynn
authors.forename: Leonard M
authors.initials: LM
authors.lastname: Shapiro
authors.forename: Bushra S
authors.initials: BS
authors.lastname: Rana
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000000981:diagnostic imaging / Q000503:physiopathology; D016022:Case-Control Studies; D019560:Echocardiography, Three-Dimensional; D017548:Echocardiography, Transesophageal; D005260:Female; D006325:Heart Atria / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D008875:Middle Aged; D008944:Mitral Valve Insufficiency / Q000000981:diagnostic imaging* / Q000503:physiopathology*
keywords: left atrium; mitral valve regurgitation; three-dimensional transoesophageal echocardiography