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Background: Recent studies suggested that quantification of calcification (Ca) in the region of aortic valve (including cusps, annulus and aortic root) by multidetector computed tomography (CT) may be useful to corroborate aortic stenosis (AS) severity. The objectives of this study were: 1) to examine the relationship between hemodynamic AS severity and the extent of Ca measured by 128-slice dual-source CT (DSCT) within aortic valve cusps, annulus, and root, 2) to determine cut-off values of valve Ca to identify severe AS and 3) to determine whether and how the valve phenotype (i.e. bicuspid vs. tricuspid) affects this relationship.Methods: 80 consecutive patients with AS underwent: 1) Doppler echocardiography to measure peak aortic jet velocity, transvalvular gradient, aortic valve area (AVA), and systemic arterial compliance (SAC=stroke volume index/pulse pressure) and 2) DSCT to measure Ca volumetric score (CVS) at the level of: i) cusps, ii) annulus and iii) aortic root adjacent to annulus. A global CVS was calculated by adding these 3 regional scores. Receiver operator characteristic (ROC) analysis was performed to determine optimal cut-off values to identify severe AS defined by an AVA<1cm2 and AVAi<0.6cm2/m2.Results: There was good correlation between mean gradient and aortic cusps CVS (r=0.69, p<0.0001), a weak correlation between gradient and aortic annulus CVS (r=0.22, p=0.05) and no correlation with aortic root CVS. Correlation with gradient was not improved when using the sum of aortic cups and aortic annulus CVSs (r=0.67) or global CVS (r=0.66). Aortic root CVS correlated only with SAC (r=-0.34, p=0.008). Correlation between gradient and aortic valve cups CVS or global CVS were much stronger in patients with tricuspid valve (r=0.81 and r=0.75) than in those with bicuspid valve (r=0.48 and r=0.53). Area under the ROC curve for identification of severe AS was 0.76 in whole cohort, 0.82 in patients with tricuspid valve and 0.55 in patients with bicuspid valve. Cut-off value of aortic cusps CVS providing the best percentage of correct classification (81%) in whole cohort was 1.37 cm3, which corresponded to 1440 Agatston units.Conclusion: Theses findings suggest that the main determinant of the hemodynamic severity of AS is Ca deposit within aortic valve cusps and that calcium deposit in aortic annulus or root have negligible impact on valve hemodynamics. Valve Ca volumetric scoring by DSCT may be helpful to corroborate stenosis severity in AS patients, particularly in those with low flow, low gradient. However, the performance of DSCT was inferior in patients with bicuspid valve.