Raghuram Mallya MD, Abstract Co-Author: Nothing to Disclose

Matthew Sewell, Abstract Co-Author: Nothing to Disclose

Matisyahu Shulman, Abstract Co-Author: Nothing to Disclose

Donna Zwas MD, Abstract Co-Author: Nothing to Disclose

Ethan Joseph Halpern MD, Presenter: Grant, Bristol-Myers Squibb Company Equipment support, Toshiba Corporation

Quantitative assessment of the left ventricular outflow tract (LVOT) and aortic valve area (AVA) are required for medical and surgical decisions related to aortic stenosis.  In clinical practice, LVOT diameter is measured by transthoracic echocardiography (TTE).  The LVOT is assumed to have a circular shape (LVOT area = πr2). AVA is calculated with the continuity equation, based upon LVOT area and outflow velocities measured by TTE. We compared CT planimetry to TTE for assessment of the LVOT and AVA.

Patients who had undergone TTE and coronary CT angiography (CCTA) within a 60 day period were retrospectively identified based upon review of our CT database.  CT images of the aortic valve and LVOT were reconstructed at 10% intervals throughout the cardiac cycle.  AVA was computed with the continuity equation on TTE and by direct planimetry during mid-systole on CCTA. Planimetry was performed by two blinded observers.  In order to determine the impact of LVOT measurement differences on AVA, AVA was recomputed after substituting the values for LVOT diameter and LVOT area measured by CCTA.

TTE measurements of AVA varied from 0.6-7.0cm2 (mean 2.5cm2), and included 10 patients with moderate to severe aortic stenosis (AVA≤1.5cm2).  There was little difference between CT and TEE measurement of LVOT diameter (mean difference: 0.05cm, p=0.37), but CT planimetry provided significantly higher measurements for LVOT area (mean difference: 0.63cm2, p=0.0002).  AVA measured by CT planimetry was significantly higher than that computed by continuity equation (mean difference: 0.61cm2, p=0.0037).  When CT measurements of LVOT area were substituted into the continuity equation in place of LVOT diameter, correlation between CT planimetry and continuity equation for AVA improved from r=0.65 to r=0.88, while mean difference in AVA between CT planimetry and continuity equation decreased to 0.17cm2 (p=0.36).

AVA calculated with the continuity equation during TTE is significantly lower than AVA by CT planimetry.  This difference is related to differences in the estimated LVOT area based upon LVOT diameter (using πr2 to compute LVOT area) versus direct measurement of LVOT area by planimetry.

CT planimetric measurements of AVA are systematically higher than TTE estimates of AVA based upon the continuity equation because LVOT area is underestimated by measurement of LVOT diameter.

Mallya, R, Sewell, M, Shulman, M, Zwas, D, Halpern, E, Differences in Aortic Valve Area Measured by CT Planimetry and Echocardiography (Continuity Equation) Are Related to Divergent Estimates of Left Ventricular Outflow Tract Area.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6006173.html