Geometric shape-derived CCTA resistance metrics predict invasive FFR in anomalous right coronary arteries under adenosine and dobutamine stress

Background Risk stratification in right anomalous aortic origin of a coronary artery (R-AAOCA) remains challenging. Conventional diameter- and area-based stenosis metrics assume circular geometry and may underestimate hemodynamic relevance in the slit-like, elliptical lumens typical of R-AAOCA. Fluid-dynamics principles suggest that perimeter-dependent resistance may better capture flow limitation. We hypothesized that shape-aware geometric indices derived from coronary computed tomography angiography (CCTA) outperform conventional metrics for predicting invasive fractional flow reserve (FFR). Purpose To compare the ability of traditional versus shape-aware CCTA-derived geometric parameters to predict hemodynamically significant stenosis in R-AAOCA, using invasive FFR under both adenosine and dobutamine stress as reference standards. Methods Consecutive patients with R-AAOCA who underwent CCTA and invasive FFR during adenosine and dobutamine stress are included in the analysis. CCTA-derived geometric characterization included ostial and intramural lumen area (ILA) measurements, shape descriptors, elliptic ratio (ER = Dmajor/Dminor), circularity (C = 4πA/P²), shape-aware stenosis metrics, including effective and hydraulic diameter stenosis ratios (EDSR, HDSR), based on ED= and HD=4A/P (A = area, P = wetted perimeter). Resistance-based indices integrated geometric severity with lesion extent and angulation, including the resistance index (RI=L×P⁴/A⁴; L=stenosis length), ostial angulation penalty (OAP=Aostial/Aref×[1+tanθ]; θ=take-off angle), and a comprehensive stenosis score (CSS=RI×ER×[1+sinθ]). Hemodynamic significance was defined as FFR ≤0.80. Results A total of 81 patients with R-AAOCA were analyzed. Hemodynamically significant stenosis was present in 6.2% of patients during adenosine stress and 19.8% during dobutamine stress. Figure 1 shows top-performing parameters. Compared to adenosine reference standard, the RI demonstrated high discrimination (AUC=0.97) and achieved 100% sensitivity with 95% specificity at the optimal cutoff. Compared to dobutamine reference standard, overall discrimination was reduced; the ostial minor diameter showed the highest predictive performance (AUC = 0.85) with 100% sensitivity but lower specificity (57%). Resistance-based indices retained strong correlation with FFR under both stress modalities. Conclusion Shape-derived, physics-informed CCTA parameters demonstrate high discriminatory performance for identifying hemodynamically significant AAOCA. Resistance-based indices were among the top predictors when referenced to adenosine FFR, whereas minor diameter measurements showed the highest predictive performance relative to the dobutamine reference standard, suggesting that stress-related dynamic changes may contribute beyond static geometry. These findings support integrating shape-aware geometric assessment into R-AAOCA evaluation to enhance non-invasive risk stratification.