Doppler echocardiographic assessment of the valve area in patients with atrioventricular valve stenosis by application of the continuity equation

Objective Due to its circular shape, the area of the proximal left ventricular tract (PLVOT) adjacent to aortic valve can be derived from a single linear diameter. This is also the location of flow acceleration (FA) during systole, and pulse wave Doppler (PWD) sample volume in the PLVOT can lead to overestimation of velocity (V1) and the aortic valve area (AVA). Therefore, it is recommended to derive V1 from a region of laminar flow in the elliptical shaped distal LVOT (away from the annulus). Besides being inconsistent with the assumptions of continuity equation (CE), spatial difference in the location of flow and area measurement can result in inaccurate AVA calculation. We evaluated the impact of FA in the PLVOT on the accuracy of AVA by continuity equation (CE) in patients with aortic stenosis (AS). Methods CE-based AVA calculations were performed in patients with AS once with PWD-derived velocity time integral (VTI) in the distal LVOT (VTILVOT) and then in the PLVOT to obtain a FA velocity profile (FA-VTILVOT) for each patient. A paired sample t-test (P < 0.05) was conducted to compare the impact of FA-VTILVOT and VTILVOT on the calculation of AVA. Result There were 46 patients in the study. There was a 30.3% increase in the peak FA-VTILVOT as compared to the peak VTILVOT and AVA obtained by FA-VTILVOT was 29.1% higher than obtained by VTILVOT. Conclusion Accuracy of AVA can be significantly impacted by FA in the PLVOT. LVOT area should be measured with 3D imaging in the distal LVOT.

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Abstract 17783: Improved Aortic Valve Area Calculation Using a Novel Biplane Echo Continuity Equation

Circulation ◽

10.1161/circ.132.suppl_3.17783 ◽

2015 ◽

Vol 132 (suppl_3) ◽

Author(s):

Thorsten M Leucker ◽

Edward P Shapiro

Keyword(s):

Aortic Valve ◽

Continuity Equation ◽

Simple Calculation ◽

Ventricular Outflow Tract ◽

Left Ventricular ◽

Aortic Valve Area ◽

Single Plane ◽

Chamber View ◽

Transcatheter Aortic Valve ◽

Valve Area

The aim of this study was to improve the accuracy of transthoracic echo- cardiographic (TTE) assessment of the aortic valve area (AVA) in patients with aortic stenosis (AS). The traditional continuity equation (CE) for determining AVA requires a measurement of left ventricular outflow tract (LVOT) area, which is calculated from a linear LVOT dimension using the parasternal long axis view, assuming circular geometry. However, routine use of multidetector computed tomography (MDCT) in patients undergoing evaluation for transcatheter aortic valve replacement (TAVR) has shown that the LVOT is elliptical rather than round. Assumption of circular geometry may introduce inaccuracies into AVA assessment. A total of 61 patients (76 ± 11 years of age, 61% men) with isolated calcific AS (mean gradient 42 ± 9 mm Hg; ejection fraction 56 ± 11%) underwent Doppler TTE as part of pre TAVR or aortic valvuloplasty evaluation. AVA was calculated by TTE using two near- perpendicular planes (parasternal long axis and apical five chamber view) to evaluate the LVOT. A modified CE was used to calculate AVA (cm2) = (π((D1 x D2)/4)x LVOT VTI)/(AV VTI) in order to account for the elliptical rather than round shape of the LVOT. AVA measurements from the traditional and modified CE were compared to invasive AVA assessment. Biplane (Figure, Panel B+D) vs. traditional single plane (Panel A+C) TTE measurement of the LVOT yielded a significantly improved positive correlation between TTE and invasive AVA assessment (r2=0.861 vs. 0.296) and a markedly reduced mean error (0.07 cm2 vs. 0.18 cm2), p<0.001. Utilizing the proposed modified continuity equation greatly improves the accuracy of TTE guided AVA measurements. This simple calculation can be performed using standard TTE without additional costly equipment (ie, biplane transducers), without additional echo views (ie, more sonographer time), and without the need to subject patients to further invasive or non- invasive testing (ie, TEE or MDCT).

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