The following are key points to remember from this article on reconciling echocardiography, computed tomography (CT), and hybrid imaging in assessing discordant grading of aortic stenosis (AS) severity:

1. There is no single modality or parameter able to accurately grade AS severity in all patients. Among patients with concordant grading on echocardiography (echo)/Doppler (both gradients and aortic valve area [AVA] suggest severe AS, or both gradients and AVA suggest nonsevere AS), then additional imaging is not required. However, among patients with discordant data, a step-by-step integrative approach that includes several imaging modalities and parameters of AS severity should be considered.
2. Hemodynamic assessment of AS severity on echo/Doppler includes flow-dependent measurements (V_max, mean gradient) and relatively flow-independent measurements (effective orifice area [EOA], Doppler velocity index). Severe AS is associated with V_max ≥4.0 m/s, mean gradient ≥40 mm Hg, EOA ≤1.0 cm², EOA index ≤0.6 cm²/m², and Doppler index <0.25). However, up to 40% of patients with AS on echocardiography have discordant measures of AS severity, most commonly with small EOA but low V_max and low Doppler-derived gradients.
3. In many patients with AS, the left ventricular outflow tract (LVOT) is elliptical in cross section; the use of two-dimensional echo measures the small axis of that ellipse, and underestimates the LVOT cross-sectional area, in turn underestimating AVA (EOA) and stroke volume index (SVI).
4. Among patients with discordant data suggesting low-flow (SVI <35 ml/m), low-gradient severe AS (mean gradient <40 mm Hg, EOA ≤1.0 cm²), potential errors in echo/Doppler data should be assessed first.
• The LVOT is probably best measured at the level of the AV annulus, rather than deeper into the LVOT.
• Velocities (and gradients) across the AV should be sampled from multiple windows; failure to interrogate the AV from nonapical windows (e.g., right sternal border, suprasternal notch) may result in underestimation of velocities and gradients in up to 50% of patients.
5. If data are still discordant and suggestive of low-flow, low-gradient severe AS, additional testing may be required:
• Hybrid imaging may be useful. Either three-dimensional echo (transthoracic or transesophageal) or contrast-enhanced CT can be used to better define the LVOT cross-sectional area; the AVA is calculated using the three-dimensionally derived LVOT area paired with Doppler velocities.
• Among patients with reduced LV ejection fraction (LVEF) (<50%), consideration should be given to low-dose dobutamine stress echocardiography (DSE) to distinguish severe from pseudosevere AS. However, DSE may not be helpful unless the LV stroke volume increases by ≥20%.
• Among patients with normal LVEF, and among patients with reduced LVEF but equivocal results with DSE, noncontrast CT may be useful to assess the AV calcium score. (Severe AS is associated with an AV calcium score ≥2,000 Agatston units in mean and ≥1,200 Agatston units in women.)

Clinical Topics: Noninvasive Imaging, Valvular Heart Disease, Computed Tomography, Echocardiography/Ultrasound, Nuclear Imaging

Keywords: Aortic Valve Stenosis, Diagnostic Imaging, Echocardiography, Echocardiography, Doppler, Echocardiography, Stress, Echocardiography, Transesophageal, Heart Valve Diseases, Multimodal Imaging, Plaque, Atherosclerotic, Stroke Volume, Tomography, Tomography, X-Ray Computed

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