Differences in Flow-Gradient Patterns Between Severe Bicuspid Aortic Stenosis and Severe Tricuspid Aortic Stenosis　― Mechanistic Insight From Multimodal Imaging ―

BACKGROUND: We investigated the flow-gradient pattern characteristics and associated factors in severe bicuspid aortic stenosis (AS) compared with severe tricuspid AS. METHODS AND RESULTS: A total of 252 patients with severe AS (115 bicuspid vs. 137 tricuspid) who underwent aortic valve (AV) replacement were retrospectively analyzed. Patients were classified into 4 groups according to stroke volume index and mean pressure gradient across the AV [normal-flow-high-gradient (NF-HG), low-flow-high-gradient, normal-flow-low-gradient, low-flow-low-gradient (LF-LG)]. In 89 patients who underwent cardiac computed tomography (CT), influential structural parameters of the left ventricular outflow tract (LVOT), AV and ascending aorta were assessed. Bicuspid AS was more likely to present a NF-HG pattern (83.5% vs. 64.2%, P<0.001), and significantly fewer presented a LF-LG pattern compared with tricuspid AS. In bicuspid AS, there was a significant mismatch between geometric orifice area (GOA) on CT planimetry and effective orifice area (EOA) calculated using the echocardiographic continuity equation. Bicuspid AS presented with a larger angle between the LVOT-AV and aorta. Multivariate analysis of bicuspid AS revealed that systemic arterial compliance (β=-0.350, P=0.031) and the LVOT-AV-aorta angle (β=-0.538, P=0.001), and stroke volume index (β=0.409, P=0.008) were associated with a discrepancy between GOA and EOA. CONCLUSIONS: Flow-gradient patterns in bicuspid AS differ from those of tricuspid AS and are associated with the structural and functional characteristics of the aorta.