The mystery of defining aortic valve area: what have we learnt from three-dimensional imaging modalities?

Abstract

Aortic valve area is one of the main criteria used by echocardiography to determine the degree of valvular aortic stenosis, and it is calculated using the continuity equation which assumes that the flow volume of blood is equal at two points, the aortic valve area and the left ventricular outflow tract (LVOT). The main fallacy of this equation is the assumption that the LVOT area which is used to calculate the flow volume at the LVOT level is circular, where it is often an ellipse and sometimes irregular. The aim of this review is to explain the physiology of the continuity equation, the different sources of errors, the added benefits of using three-dimensional imaging modalities to measure LVOT area, the latest recommendations related to valvular aortic stenosis, and to introduce future perspectives. A literature review of studies comparing aortic valve area and LVOT area, after using three-dimensional data, has shown underestimation of both measurements when using the continuity equation. This has more impact on patients with discordant echocardiographic measurements when aortic valve area is disproportionate to haemodynamic measurements in assessing the degree of aortic stenosis. Although fusion imaging modalities of LVOT area can help in certain group of patients to address the issue of aortic valve area underestimation, further research on introducing a correction factor to the conventional continuity equation might be more rewarding, saving patients additional tests and potential radiation, with no clear evidence of cost-effectiveness.

Aortic Valvular Disease in Elderly Subjects with Heterozygous Familial Hypercholesterolemia: Impact of Lipid-Lowering Therapy

“…Measurements of aortic valve functionality may vary in the presence of abnormal systolic function [43]. Although it was not an exclusion criterion, none of our cases and controls had left ventricular ejection fraction (LVEF) <40% or hypertrophic cardiomyopathy, thus, this limitation does not play an important role in our study, and all measurements of the valvular surface could be performed by continuity equation, the best standardized procedure.…”

Mid-term effect of balloon aortic valvuloplasty on mitral regurgitation in aortic stenosis

“…The incidence of aortic stenosis (AS) is increasing as a result of aging of the general population, with poor survival anticipated without aortic valve replacement once symptoms develop [1,2]. Balloon aortic valvuloplasty (BAV) is offered as an alternative to conventional surgical aortic valve replacement (SAVR) or transcatheter aortic valve replacement (TAVR) for elderly and frail patients with severe AS, for whom there are no other effective options [3].…”

Discrepancy of Aortic Valve Area Measurements by Doppler vs. Biplane Stroke Volume Measurements and Utility of Combining the Different Areas in Aortic Valve Stenosis ― The Asian Valve Registry ―

“…11 LVOT diameter was measured at the level of the aortic valve annulus in a zoomed long-axis image. 12 In the apical 3-chamber view, the pulsed-wave Doppler sample volume was placed in the center of the LVOT, and the obtained velocity-time integral (VTILVOT) was manually measured by tracing the modal velocity, 3 and its cross-sectional area (CSA) was calculated as 3.14 × (LVOT diameter) 2 / 4. SVDoppler was obtained as CSALVOT × VTILVOT.…”

“…Outlines of the signals were traced to obtain the peak pressure gradient (PG), mean PG, and VTI at the aortic valve level (VTIAV). AVADoppler was estimated by the continuity equation as follows: 2,3 AVADoppler = SVDoppler / VTIAV = CSALVOT × VTILVOT / VTIAV AVABiplane was calculated as follows: AVABiplane = SVBiplane / VTIAV = (LVEDV -LVESV) / VTIAV All volume, area and length measurements were normalized by body surface area (BSA) and denoted accordingly with the suffix I.…”

“…5 Elderly subjects A ortic valve stenosis (AS) is one of the most common valvular diseases and the third most common cardiovascular disease in developed countries. 1 Aortic valve area (AVA), a standard parameter of the severity of AS, is routinely derived using the continuity equation, 2,3 for which the stroke volume (SV) is obtained either by Doppler or biplane Simpson [left ventricular end-diastolic volume (LVEDV) − LV end-systolic volume (LVESV)] method (SVDoppler and SVBiplane, respectively).…”