Planimetry of Aortic Valve Area Using CTA: Cutoff Derivation for Stenotic Bicuspid and Tricuspid Valves.

BACKGROUND

Computed tomography based planimetric assessment of the anatomic aortic valve area (aAVACTA) in aortic stenosis is routinely performed. Unlike transthoracic echocardiography (TTE)-based effective AVA by TTE, it lacks clearly defined severity cutoff values, limiting clinical utility.

METHODS

In this retrospective single-center analysis with computed tomography angiography data from 2013 to 2025, cutoffs were determined from 1294 TTE-based conclusive severe or nonsevere patients by congruence of maximum velocity, mean pressure gradient, and effective AVA by TTE. In separate receiver operator curves analyses for tricuspid and bicuspid valves, the severe stenosis likely cutoff was defined by Youden index and the unlikely cutoff by a negative likelihood ratio <0.1. Cutoffs were internally validated in 480 patients, compared with the Agatston score by net reclassification index, and tested in 190 separate normal-flow low-gradient aortic stenosis cases.

RESULTS

Correlation between aAVACTA and effective AVA by TTE was moderate and strong in tricuspid and bicuspid valves, respectively (Pearson r 0.67 and 0.78; P<0.001). Severe stenosis was likely in tricuspid valves at aAVACTA ≤0.95 cm² (sensitivity 87%, specificity 78.9%) and unlikely at ≥1.10 cm² (negative likelihood ratio, 0.092). In bicuspid valves severe stenosis was likely at aAVACTA ≤1.08 cm² (sensitivity 88.3%, specificity 77.3%) and unlikely at ≥1.20cm2 (negative likelihood ratio, 0.091). Validation showed comparable results. Net reclassification index compared with the Agatston score was 0.16 for likely and 0.17 for unlikely cutoffs (P<0.001). Cutoffs were applied to 190 suspected severe low-gradient cases. Adding aAVACTA as an additional severity marker led to reclassification to nonsevere in 5.8% of cases.

CONCLUSIONS

Direct planimetry of AVA is feasible and shows utility in low gradient-aortic stenosis. However, as the hemodynamic effect is impacted by valve shape, cutoff values should differentiate between tricuspid and bicuspid valves.