Multidetector Computed Tomography and Aortic Stenosis: The Emerging Potential of Bridging Morphology and Severity Grading

<b>Background/Objectives</b>: Echocardiography is the reference standard for grading aortic stenosis (AS); however, it yields discordant severity estimates in up to 40% of patients. Multidetector computed tomography (MDCT)-derived methods for calculating aortic valve area (AVA) may improve diagnostic concordance, but their diagnostic performance, validation against invasive hemodynamics, and the influence of left ventricular outflow tract (LVOT) morphology on severity grading remain insufficiently investigated. <b>Methods</b>: We retrospectively analyzed 307 patients with normal-flow, high-gradient calcific AS who underwent echocardiography, MDCT, and cardiac catheterization. AVA was calculated using (1) echocardiographic LVOT diameter, (2) hybrid Doppler-MDCT planimetric LVOT area, and (3) corrected echocardiographic LVOT diameter (×1.13). Agreement, correlation, and diagnostic performance were assessed using Bland-Altman analysis, Pearson correlation, ROC analysis, and McNemar's test. Subgroups defined by diagnostic concordance and MDCT-derived LVOT size were compared using ANOVA. <b>Results</b>: Hybrid AVA showed a strong correlation with echocardiographic AVA (r = 0.749, <i>p</i> < 0.001), with a mean difference of +0.11 ± 0.15 cm². Both methods demonstrated similar relationships with invasive and non-invasive hemodynamic markers of AS severity. When combined with echocardiography, the hybrid method increased concordant classification of severe AS by 8%. In contrast, corrected AVA performed significantly worse, leading to more discordant classifications. LVOT size was significantly associated with variability in AVA and Doppler velocity index, independent of flow status. <b>Conclusions</b>: Hybrid MDCT-derived AVA provides diagnostic performance equivalent to echocardiography and improves concordance in selected patients. LVOT size influences key echocardiographic parameters and may warrant tailored diagnostic thresholds.