Comparative assessment of 4D CT-derived geometric and effective orifice areas in severe aortic stenosis

The geometric orifice area (GOA) measured by four-dimensional computed tomography (4D-CT) offers a flow-independent anatomical assessment of aortic stenosis (AS). However, its quantitative relationships with effective orifice areas (EOA) from echocardiography and catheterization, as well as the hemodynamic factors underlying their relationship and their relevance to markers of left-ventricular load, remain insufficiently defined.

GOA was obtained at individualized peak systole by CT planimetry, and EOA_echo and EOA_cathe were calculated using the continuity and Gorlin equations. Associations, agreement, and bias between GOA and each EOA were evaluated using correlation analysis, Passing-Bablok regression, and Bland-Altman plots. Multivariable regression identified hemodynamic determinants of EOA-to-GOA ratios. Hierarchical regression assessed the incremental explanatory value of valve area indices for preprocedural NT-proBNP.

GOA demonstrated excellent reproducibility (intraclass correlation coefficient 0.95). GOA correlated strongly with EOA_echo (r = 0.67) and EOA_cathe (r = 0.65), whereas the correlation between EOA_echo and EOA_cathe was moderate (r = 0.55). Passing-Bablok analysis revealed proportional bias for both modalities. Stroke volume index significantly increased both EOA_echo-to-GOA and EOA_cathe-to-GOA ratios. Only GOA provided a statistically significant but modest incremental explanatory value for preprocedural NT-proBNP (ΔR² = 0.03; p = 0.02), whereas neither EOA_echo nor EOA_cathe significantly improved model performance.

CT-derived GOA is a highly reproducible, flow-independent anatomical metric that correlates strongly with physiological valve areas while offering additional clinical insight. Variability in EOA-to-GOA scaling underscores the complementary roles of anatomical and functional assessments in characterizing AS severity.