Abstract
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. p]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.
Highlights
Doppler-based calculation of aortic valve area (AVA) is based on multiple assumptions of geometry and flow through the left ventricular outflow tract (LVOT) and the aortic valve (AV) [1, 2, 3, 14, 15, 16, 17]
With PLVOT being the zone of flow acceleration (FA) (Figs 3 and 4), the guidelines recommend placement of the pulse wave Doppler (PWD) sample volume 1 cm distal to the aortic leaflets in the DLVOT for V1 estimation due to laminar flow [1]
There was a 30.3% increase in peak LVOT velocity (FA-V1 = 1.095, s.d. 0.27, CI: 0.08)
Summary
Doppler-based calculation of aortic valve area (AVA) is based on multiple assumptions of geometry and flow through the left ventricular outflow tract (LVOT) and the aortic valve (AV) [1, 2, 3, 14, 15, 16, 17]. In continuity equation (Fig. 1) LVOT area, continuous wave Doppler (CWD)-derived peak transaortic velocity (V2) and pulse wave Doppler (PWD) derived peak LVOT velocities (V1). With PLVOT being the zone of flow acceleration (FA) (Figs 3 and 4), the guidelines recommend placement of the PWD sample volume 1 cm distal to the aortic leaflets in the DLVOT for V1 estimation due to laminar flow [1]. The flow acceleration is believed to result in turbulence, aliasing and incorrect V1 estimation. Whereas aliasing is self-evident, flow acceleration without aliasing that results only in a ‘step up’ in V1 without aliasing has the potential to impact continuity equationbased calculations
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