Underestimation of aortic valve area in calcified aortic valve disease: Effects of left ventricular outflow tract ellipticity

BackgroundThe aortic valve area (AVA) is usually calculated using the continuity equation (CE) in which the left ventricular outflow tract (LVOT) area is estimated assuming circular geometry. We sought to evaluate the LVOT ellipticity with 64-multidetector computed tomography (MDCT) and to assess the impact of LVOT ellipticity on the evaluation of CE-based AVA in patients with calcified aortic valves.MethodsWe prospectively studied 110 patients with calcified aortic valves including 54 aortic stenosis (AS) with both 64-MDCT and transthoracic echocardiography. Double oblique transversal images for planimetry of the aortic valve and LVOT were obtained during the midsystolic phase. The short and long-axis diameters of the planimetered LVOT were measured.ResultsThe MDCT planimetered LVOT area was underestimated by the diameter-derived (π × r2) LVOT area using echocardiography (444 ± 70 mm2 versus 369 ± 63 mm2; p < 0.001). The mean difference in AVA values calculated using the CE and planimetry was 0.43 ± 0.23 cm2 and mean measurement error of CE-based AVA was 18%. When the CE-based AVA was corrected using the MDCT planimetered LVOT area, the measurement error decreased from 28 ± 5 to 5 ± 2% in patients with severe aortic stenosis (AVA < 1.0 cm2), whereas from 16 ± 5 to 3 ± 6% in others.ConclusionEllipticity of LVOT is associated with underestimation of AVA measurements using the CE. CE-based AVA corrected with MDCT planimetered LVOT area is useful especially in severe AS.