title: Three-dimensional imaging of the left ventricular outflow tract: impact on aortic valve area estimation by the continuity equation.
abstract: BACKGROUND
  Measurement of left ventricular outflow tract (LVOT) area for estimation of aortic valve area (AVA) using two-dimensional (2D) transthoracic echocardiography (TTE) and the continuity equation assumes a round LVOT. The aim of this study was to compare measurements of LVOT area and AVA using 2D and three-dimensional (3D) TTE and cardiac computed tomographic angiography (CCTA) in an attempt to improve the accuracy of AVA estimation using TTE.
  
  
  METHODS
  Fifty patients were prospectively studied, 25 with aortic stenosis and 25 without aortic stenosis (group 1). LVOT area and AVA were estimated using 2D TTE, and LVOT area and diameters were measured using 256-slice CCTA and 3D TTE. AVA was also planimetered using CCTA in midsystole. LVOT area and AVA estimated by 2D TTE were correlated with measurements by 3D TTE and CCTA. Findings from group 1 were then validated in 38 additional patients with aortic stenosis (group 2).
  
  
  RESULTS
  LVOTs were oval in 96% of the patients in group 1, with a mean eccentricity index (diameter 2/diameter 1) of 1.26 ± 0.09 by CCTA. Compared with CCTA, 2D TTE systematically underestimated LVOT area (and therefore AVA) by 17 ± 16%. The correlation between CCTA and 3D TTE LVOT area was only moderate (r = 0.63), because of inadequate 3D transthoracic echocardiographic image quality. Mean AVA was 0.92 ± 0.44 cm(2) by 2D TTE and 1.14 ± 0.68 cm(2) by CCTA (P = .0015). After correcting AVA on 2D TTE by a factor of 1.17 (accounting for LVOT area ovality), there was no difference between 2D TTE and CCTA (0.06 ± 26 cm(2), P = .20, r = 0.86). In group 2, 2D TTE underestimated LVOT area and AVA by 16 ± 11%, similar to group 1, and AVA by TTE was 0.75 ± 0.14 cm(2) compared with 0.88 ± 0.21 cm(2) by CCTA (P < .0001). When the correction factor was applied to the group 2 results, the corrected AVA by 2D TTE (×1.17) was 0.87 ± 0.17 cm(2), similar to AVA by CCTA (P = .70).
  
  
  CONCLUSIONS
  Three-dimensional imaging revealed oval LVOTs in most patients, resulting in underestimation of LVOT area and AVA on 2D TTE by 17%. This accounted for the difference in AVA between 2D TTE and CCTA. Current 3D TTE is inadequate to accurately measure LVOT area.
authors.affiliation: Department of Radiology, Lady Davis Carmel Medical Center and the Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel.
authors.forename: Tamar
authors.initials: T
authors.lastname: Gaspar
authors.forename: Salim
authors.initials: S
authors.lastname: Adawi
authors.forename: Robert
authors.initials: R
authors.lastname: Sachner
authors.forename: Ihab
authors.initials: I
authors.lastname: Asmer
authors.forename: Majdi
authors.initials: M
authors.lastname: Ganaeem
authors.forename: Ronen
authors.initials: R
authors.lastname: Rubinshtein
authors.forename: Avinoam
authors.initials: A
authors.lastname: Shiran
mesh_terms: D000368:Aged; D000465:Algorithms; D001021:Aortic Valve / Q000000981:diagnostic imaging*; D001024:Aortic Valve Stenosis / Q000150:complications / Q000000981:diagnostic imaging*; D019560:Echocardiography, Three-Dimensional / Q000379:methods*; D005260:Female; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014694:Ventricular Outflow Obstruction / Q000000981:diagnostic imaging* / Q000209:etiology