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Method for separate analysis of inflow vs. outflow regions of the right ventricle in Ebstein's anomaly
Journal of Cardiovascular Magnetic Resonance volume 11, Article number: P248 (2009)
Ebstein's anomaly (EA) is caused by underdevelopment of the inlet. However the impact of EA on regional and global function in the underdeveloped inlet has been difficult to assess quantitatively.
We measured the size and shape of the right ventricle (RV) and its inlet and infundibulum (outflow) portions in 30 patients with EA aged 16–64 yrs and 9 normal subjects from MR images acquired in long and short axis and oblique views. The RV was traced and reconstructed in 3D as a triangular mesh using the piecewise smooth subdivision surface method. To define the volumes of the inlet and infundibulum, points were traced at the muscular ring separating the two portions, focusing on the supraventricular crest and the parietal, septal, and moderator bands. Care was taken to confirm the locations of these anatomic landmarks in intersecting views. A plane was fit to the points and used to cut the RV into inlet and infundibulum. Wall motion was measured in 13 regions by the centersurface method along chords drawn orthogonal to a surface constructed midway between the end diastolic (ED) and end systolic (ES) surfaces. The lengths of chords in each region were averaged and then normalized by dividing by the square root of body surface area. Tricuspid tilt was defined as the angle between the mitral and tricuspid annular planes, and tricuspid descent was the systolic excursion of the annulus centroid. See Figure 1.
The global RV ejection fraction (EF) was mildly depressed in EA patients (45 ± 8 vs. 55 ± 4% in normals, p < 0.001). Their RV's were severely dilated (end diastolic volume index 185 ± 78 vs. 82 ± 16 ml/m2, p < 0.001) and rounded in apical and mid RV cross sections. The tricuspid annulus was severely tilted (62 ± 26 vs. 19 ± 9° in normals, p < 0.001). The infundibulum contained approximately 1/5th of RV volume in both groups (20 ± 7 in normals vs. 21 ± 9% in EA, p = NS). In EA patients inlet EF exceeded infundibulum EF (46 ± 7 vs. 38 ± 13%, p < 0.02). However the function of both inlet and infundibulum were depressed compared to normal (p < 0.05 for both). The function of the inlet and infundibulum differed less in normals (55 ± 6 vs. 49 ± 11%, p = NS). Regional function was depressed compared to normal in all 9 inlet regions, significantly so in 4 regions. Tricuspid descent was also depressed compared to normal (13 ± 5 vs. 18 ± 3 mm, p < 0.005) but the pattern of regional function was similar to normal with the greatest contraction occurring in basal regions. The global EF correlated with wall motion in the basal regions and inlet septum (r between 0.43 and 0.58, p < 0.05) and with tricuspid annular descent (r = 0.52, p < 0.005).
Despite underdevelopment of the inlet, patients with EA have relatively preserved function in this portion of the RV. Three dimensional surface reconstruction enables separate analysis of the inlet and infundibulum portions of the RV as well as detailed assessment of regional function and shape.
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Lee, C., Sheehan, F., Bouzas, B. et al. Method for separate analysis of inflow vs. outflow regions of the right ventricle in Ebstein's anomaly. J Cardiovasc Magn Reson 11, P248 (2009). https://doi.org/10.1186/1532-429X-11-S1-P248
- Right Ventricle
- Tricuspid Annulus
- Subdivision Surface
- Global Ejection Fraction
- Right Ventricle Ejection Fraction