Stability of the valve-to-annular ratio (anatomical reserve) as a biological constant in symptomatic severe aortic stenosis across clinical phenotypes

Introduction

Echocardiography remains the first line imaging modality for aortic stenosis (AS); although discordant findings occur in around one third of patients.(1,2) Computed tomography derived aortic valve area (CT AVA) is larger than echocardiographic Aortic Valve Area (AVA), yet neither demonstrates improved correlation with transvalvular gradients nor greater specificity for severe AS.(3,4) We evaluated valve to annular ratio as anatomical reserve for its ability to improve the specificity for severe AS and obviate the effect of flow.

Methods

A retrospective cohort study was conducted on 107 symptomatic patients with severe aortic stenosis (AS) being worked up for TAVI. Sub-groups were indentified: High Gradient (HG, N=69), Classical Low-Flow Low-Gradient (LFLG, N=16), Paradoxical LFLG (pLFLG, N=2), Bicuspid (BAV, N=7), and Mixed aortic stenosis/regurgitation (AS/AR) (N=13). Data was integrated from transthoracic echocardiography (TTE) and ECG-gated computed tomography (CT). AVA was derived using: Echo-CE: Standard Doppler derived AVA using continuity equation, AVA-CT: Direct CT planimetry of the aortic valve systolic orifice, AVA-Hybrid: Integration of CT-derived annular area with Echo derived Doppler velocities.

Spearman rank-order correlation (r) analysis assessed association between Echo-CE and AVA-CT within each subgroup. To quantify the Anatomical Reserve Valve to Annular Ratio (VA Ratio) was calculated as AVA-CT divided by the CT annular area. This dimensionless index was assessed across all phenotypes.

Results

The median age of the cohort was was 81 [IQR: 77–85] years with 70% males. Low correlation coefficients with large confidence intervals indicated significant discordance between measurement modalities (P < 0.001 for HG and LFLG). Echo-CE consistently yielded lower values than AVA-CT (0.72 vs 0.93cm2 in HG), while AVA-Hybrid yielded higher values (1.18 cm2). Correlation between Echo and CT derived AVA was low to moderate across different flow states (HG: r=0.27; LFLG: r=0.43) and in the Mixed AR/AS group (r=0.43) (table 1).

Despite this discordance, the VA Ratio (Anatomical Reserve) proved to be a robust biological constant for symptomatic severe AS, with a total cohort median of 0.22 [IQR: 0.18–0.26]. Phenotypic analysis confirmed the stability of this 22% threshold regardless of flow or gradient. Notably, Paradoxical LFLG patients exhibited the lowest anatomical reserve (Ratio: 0.18), while Mixed AR/AS patients possessed the highest (Ratio: 0.24) (figure1).

Conclusion

CT AVA demonstrated a weaker correlation to echo AVA by CE in high gradient and classical low flow low gradient AS. Anatomical reserve (valve to annular ratio) may represent a novel dimensionless anatomical index to grade severity of aortic stenosis. This has been shown to reveal limitations of CT aortic valve calcium score for grading severity of AS.(5) Larger studies are required to validate these findings prior to clinical implementationFigure 1.Table 1