Abstract 10768: Evaluation of Left Ventricular Outflow Tract (LVOT) Geometry Using Cardiac Computed Tomographic Angiography; Comparison of Different Methods of Assessing LVOT Area; Implications for Calculation of Aortic Valve Area
Background: The echocardiographic (echo) assessment of aortic valve area (AVA) is performed with the assumption that the LVOT is circular. However, recent data has suggested otherwise. We further evaluated LVOT geometry using cardiac computed tomography angiograms (CTA) and compared different methods of assessing LVOT area.
Methods: Using 3D multiplanar reconstruction, the anterior-posterior diameter (APD) was noted in short-axis. An orthogonal line to the AP dimension defined the medio-lateral diameter (MLD). LVOT area was directly planimetered. An eccentricity index ( EI) of the LVOT was defined as APD/MLD - 1.
Results: Of the 302 patients, the APD was consistently shorter than the MLD by 0.37 cm ± 0.18 cm ( p< 0.0001). The regression equation was: MLD= 0.50 * 0.94 APD (r2= 68%, p< 0.0001). This is consistent with the finding that the mean EI was −0.13 ± 0.06 (p<0.0001). Furthermore, the LVOT area derived using APD/2 as the radius of a circle (LVOT area-πr2) was consistently smaller than the 3D planimetered LVOT area (LVOT area-plan) by 0.64 cm2 ± 0.43 cm2 (p< 0.0001). The regression equation was: LVOT area-plan = 0.70 + 0.99* LVOT area-πr2 ( r2= 85%, p<0.0001). However, when the LVOT area derived from the ellipsoid formula (LVOT area-ellipse) using both APD and MLD was compared to the LVOT area-plan, there was no significant difference between the two (p=0.17). Overall, mean LVOT area-πr2 was underestimated by 12.9% ± 8.4% when compared to LVOT area-plan. Subdividing patients with more pronounced EIs into three categories showed an even greater underestimation of LVOT area by the LVOT area-πr2 method compared to LVOT area-plan. Patients with EIs > −0.13 (n=133), −0.13 to −0.20 (n=129), −0.20 to −0.23 (n=33), and −0.24 to−0.269 (n=7) were underestimated by 8.4%, 15.0%, 20.6%, and 24.9%, respectively (p<0.0001).
Conclusions: The LVOT is elliptical, with APD being consistently smaller than the MLD. The sole use of APD in the calculation of LVOT area using πr2, results in significant underestimation of LVOT area, which can also have significant consequences for AVA calculation. Underestimation of LVOT area can be avoided using direct planimetry or an elliptical formula. If MLD cannot be imaged, a regression equation can be used to estimate MLD from APD.
- © 2011 by American Heart Association, Inc.