Inconsistent Echocardiographic Grading of Aortic Stenosis: Is the Left Ventricular Outflow Tract Important?
How does left ventricular outflow tract (LVOT) diameter measurement affect inconsistencies in the echocardiography/Doppler assessment of aortic stenosis (AS) severity?
In a retrospective cross-sectional analysis, patients were identified who had undergone echocardiography at Mayo Clinic between 2000 and 2010, and had findings including LV ejection fraction (EF) ≥50%, aortic valve mean gradient ≥20 mm Hg, aortic valve area (AVA) ≤2.5 cm2, and < moderate (2+) aortic regurgitation. Patients were divided into three groups based on LVOT diameter: “small” LVOT (1.7-1.9 cm), “average” (2.0-2.2 cm), and “large” LVOT (≥2.3 cm). In each group, inconsistency of data for classification of severity of AS was assessed, and alternative thresholds were explored.
Of 9,488 patients, 58% were men. LVOT diameter was 2.18 ± 0.19 cm, peak velocity (Vmax) was 3.9 ± 0.8 m/s, mean gradient was 37 ± 16 mm Hg, and AVA was 1.09 ± 0.34 cm2. Patients with a small LVOT tended to be older women (91%), with worse systemic hemodynamics and more prevalent paradoxical low-flow low-gradient AS compared to patients with average and large LVOT diameter (all parameters p < 0.001). Despite clinically similar mean gradient and Vmax across all groups, mean AVA ranged from 0.88 to 1.25 cm2 (p < 0.001), classifying more patients with small LVOT diameter as severe AS, patients with average LVOT diameter as moderate-severe AS, and patients with large LVOT diameter as moderate AS. For patients with large, average, and small LVOT diameter, an AVA of 1.0 cm2 corresponded to mean gradients of 42 mm Hg, 35 mm Hg, and 29 mm Hg; Vmax of 4.1 m/s, 3.8 m/s, and 3.5 m/s; and dimensionless index (DI) of 0.22, 0.29, and 0.36, respectively. An AVA cut-off of 0.8 cm2 reduced severe AS inconsistency from 48% to 26% for patients with small LVOT diameter; and an AVA cut-off of 0.9 cm2 reduced severe AS inconsistency from 37% to 26% for patients with average LVOT diameter. The current AVA cut-off of 1.0 cm2 was consistent for patients with a large LVOT diameter.
Based on current guidelines, small, average, and large LVOT diameters are associated with significant inconsistencies in the assessment of AS severity. For patients with normal EF and normal flow, current guideline definitions of severe AS are most consistent for patients with large LVOT diameter, but not so for patients with average or small LVOT diameter. In those patients, lower AVA cut-offs should be further studied. The DI threshold for severe AS is highly variable depending on the LVOT diameter, and guideline revision of this threshold should be considered.
There is no perfect single criterion for the echo/Doppler determination of AS severity; current American College of Cardiology/American Heart Association and European Society of Cardiology guidelines include assessment of peak velocity (Vmax), mean gradient, effective orifice area, and DI (the ratio of LVOT to aortic valve velocity-time integrals). Measurement of the LVOT diameter is an important source of error in the calculation of effective orifice area due to potential inaccuracies in measurement and in the precise measurement location. Recent use of cardiac computed tomography among patients with AS (typically in the context of evaluation for transcatheter aortic valve replacement) reinforces important limitations regarding geometric assumptions made about the LVOT––that it is round and cylindrical. This study finds inconsistency in the assessment of AS severity based on the measured diameter of the LVOT, and the authors suggest guideline revisions based on these. Of equal importance will be re-examining LVOT diameter measurement location and assumptions of its circular geometry, as well as continued recognition that no single measurement is flawless and that an integrated approach is advisable in the assessment of valve disease severity.
Keywords: Echocardiography, Doppler, Heart Valve Prosthesis, Tomography, X-Ray Computed, Cross-Sectional Studies, Hemodynamics, United States
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