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We sought to determine the accuracy of multislice spiral computed tomography (MSCT) for assessing of aortic valve stenosis and to establish threshold values of the planimetric aortic valve orifice area (AVA) that best separate between different grades of stenosis severity.A total of 202 patients (among them 160 patients with aortic valve stenosis) underwent MSCT, transthoracic echocardiography (TTE) and cardiac catheterization (CATH). Planimetric AVA measurements at MSCT were compared with calculations based on Doppler flow velocity measurements by TTE (using the continuity equation) and pressure gradient measurements by CATH (using the Gorlin formula).Series of AVA measurements correlated well between MSCT and TTE (r = 0.86) and between MSCT and CATH (r = 0.90). However, AVA at MSCT (0.98 ± 0.47 cm2) was significantly larger than AVA at TTE (0.81 ± 0.36 cm2; P < 0.05) and CATH (0.80 ± 0.39 cm2; P < 0.05). For severity grades 0 through IV the AVAs at MSCT were 2.69 ± 0.75, 1.86 ± 0.30, 1.48 ± 0.17, 0.95 ± 0.20, and 0.68 ± 0.20 cm2, respectively. For separating, the 5 severity grades optimal thresholds at MSCT were 2.1, 1.6, 1.2, and 0.9 cm2. Using these adjusted thresholds there was perfect agreement in classification between MSCT and CATH in 156 (77%), but a mismatch by 1 grade in 43 (21.5%) and 2 grades in 3 (1.5%) patients (κw = 0.86).Planimetric AVA measurements on MSCT allows for an accurate grading of aortic valve stenosis severity. However, AVA measurements on MSCT are usually larger than measurements on TTE and CATH. Consequently, the thresholds for discriminating between different severity grades have to be adjusted in MSCT.