Validation and Characterization of Transcatheter Aortic Valve Effective Orifice Area Measured by Doppler Echocardiography
What is the best method to determine echocardiography/Doppler aortic valve effective orifice area (EOA) following transcatheter aortic valve implantation (TAVI) with the Edwards-SAPIEN prosthesis?
A total of 122 patients underwent TAVI with the use of the Edwards-SAPIEN valve (Edwards Lifesciences, Irvine, CA). The EOA was measured by transthoracic echocardiography at hospital discharge, and 6 months and 1 year after TAVI with the use of two methods, as described in previous studies. In Method #1 (EOA1), left ventricular outflow tract diameter (LVOTd) entered in the continuity equation was measured at the base of prosthesis cusps whereas, in Method #2 (EOA2), LVOTd was measured immediately proximal to the prosthesis stent.
The average EOA2 (1.57 ± 0.41 cm2) was larger (p < 0.01) than EOA1 (1.21 ± 0.38 cm2). Accordingly, the incidence of severe prosthesis-patient mismatch (indexed EOA ≤0.65 cm2/m2) was threefold lower with the use of EOA2 than with EOA1 (9% vs. 33%; p < 0.001). Mean transprosthetic gradient correlated better (p = 0.03) with indexed EOA2 (r = –0.70, p < 0.0001) than with indexed EOA1 (r = –0.58, p < 0.0001). Intra- and inter-observer variability were lower for EOA2 compared to EOA1 (intra: 5% vs. 7%, p = 0.06; inter: 6% vs. 14%; p < 0.001). Aortic annulus size was the sole independent determinant (p = 0.01) of prosthetic valve EOA2. The average EOA varied from 1.37 ± 0.23 cm2 for aortic annulus size <19 mm up to 1.90 ± 0.17 cm2 for size >23 mm.
When estimating the EOA of Edwards-SAPIEN valves by Doppler echocardiography, the authors recommend the use of LVOT diameter and velocity measured immediately proximal to the stent. The main determinant of the EOA of transcatheter valves was the patient’s annulus size. These valves provided excellent hemodynamics even in patients with a small aortic annulus.
TAVI results in aortic valve geometry that is different than the native valve, with valve leaflets within a wire mesh and positioned relatively downstream from the normal leaflet position. Because the continuity equation usually measures diameter and velocity profile within the LVOT, accommodation must be made to the altered geometry after TAVI. This study used correlation with transvalvular gradients and inter- and intra-observer variability as endpoints to determine whether EOA should be calculated from the LVOTd within the TAVI stent (proximal to the valve leaflets) or immediately proximal to the TAVI stent, and concludes that the diameter proximal to the stent is better. It appears that a single pulsed-wave Doppler measurement was captured. A likely explanation of the study findings is that the sonographer usually positions the pulsed-wave sample volume in the LVOT (not within the proximal ascending aorta); measuring proximal to the stent would better match the location of the sample volume.
Keywords: Prostheses and Implants, Incidence, Heart Valve Prosthesis, Risk Factors, Angioplasty, Heart Ventricles, Hemodynamics, Stents, Echocardiography
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