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Severity of aortic regurgitation assessed by area of vena contracta: a clinical two-dimensional and three-dimensional color Doppler imaging study
© Sato et al.; licensee BioMed Central. 2015
Received: 1 February 2015
Accepted: 17 April 2015
Published: 5 May 2015
Quantitation of aortic regurgitation (AR) using two-dimensional (2D) echocardiography, including vena contracta width (VCW) measurement, is still challenging. Three-dimensional (3D) echocardiography can directly measure the vena contracta area (VCA), regardless of the rheological characteristics. We intended to assess the possibility of 3D vena contracta area (3DVCA) as well as 2D vena contracta area (2DVCA) in the assessment of AR severity.
Sixty-one patients with AR [17 female (32.7%); mean age: 74.0 ± 10.1 years] underwent 2D and 3D color Doppler echocardiography. Using conventional 2D color Doppler imaging, we measured VCW, 2DVCA, regurgitant volume (RV), and effective regurgitant orifice area (EROA). We also measured 3DVCA manually off-line from 3D full-volume color Doppler datasets for reference. Comprehensive 2D and 3D data on AR severity were successfully obtained from 52 of the 61 (85.2%) patients.
Significant correlations existed between 2DVCA and EROA (r = 0.89; p < 0.001). The cut-off 2DVCA for grading severe AR was 34 mm2 (area under curve: 0.95; sensitivity: 78%; specificity: 95%). Significant correlations existed between 3DVCA and EROA (r = 0.89; p < 0.001). The cut-off 3DVCA for grading severe AR was 32 mm2 (area under curve: 0.96; sensitivity: 89%; specificity: 98%). Significant correlations existed between 2DVCA and 3DVCA (r = 0.97; p < 0.001).
Two-dimensional, as well as three dimensional, vena contracta area measurement is a simple technique suitable for clinical use during comprehensive Doppler echocardiographic AR assessment.
Accurate quantitation of aortic regurgitation (AR) severity is essential for effective clinical management and surgical intervention timing [1,2]. Conventional two-dimensional (2D) and color Doppler echocardiographic imaging modalities, incorporating the vena contracta width (VCW), regurgitant volume (RV), and effective regurgitant orifice area (EROA) measurement, are established methods for AR severity evaluation [3,4]. However, accurate prediction of AR severity is often challenging . The vena contracta is located in the narrowest region between the proximal laminar flow acceleration zone and the distal turbulent regurgitant jet spray. Previous studies [6-8] showed VCW measurement to be a simple, reproducible method that is less dependent on loading conditions in assessing AR severity. However, the VCW measurement might over- or underestimate AR severity because the vena contracta jet shape is not always circular, but sometimes irregular or ellipsoid. Three-dimensional (3D) echocardiography can directly measure the vena contracta area (VCA): 3DVCA measurement was proven superior to VCW measurement for AR quantitation because it provides reliable assessment of the regurgitant orifice shape [9-14]. In contrast, 3DVCA processing after data acquisition is time-consuming, and the high-end echocardiographic machine capable of 3D color Doppler imaging is not always accessible. We evaluated the feasibility of measuring the cross-sectional VCA using 2D color Doppler imaging (2DVCA) in comparison with 3DVCA in assessing AR severity.
Statistical analyses were performed using SPSS (SPSS, Inc., Chicago, IL, USA) and R (The R Foundation for Statistical Computing, Vienna, Austria). Data were expressed as mean ± standard deviation (SD), and p-values <0.05 were considered significant. To compare 2DVCA with 3DVCA and to correlate 2DVCA with EROA, we performed linear regression analyses and calculated Pearson’s correlation coefficients. To assess intraobserver variability, 2D echocardiographic data were analyzed twice off-line with a 1-week interval by the same operator. Similarly, a second observer, blinded to the results of preceding investigations, performed analyses to assess interobserver variability. Interobserver and intraobserver variability were evaluated via the intraclass correlation coefficient. Percentages of intraobserver and interobserver variability were calculated as the absolute difference divided by the average of the two measurements. Agreement was assessed using the Bland–Altman analysis. Comparison of mean values was performed using the paired t-test. We conducted receiver operating characteristic curve analysis to determine the optimal cut-off values in identifying severe AR (EROA: >30 mm2) [3-5].
Variables determining the severity of aortic regurgitation
Mean ± SD
14.9 ± 15.6
3.2 ± 1.3
14.3 ± 15.7
16.9 ± 10.3
39.8 ± 23.1
The intraclass correlation coefficient was 0.91, and intraobserver variability was 15.9 ± 13.2%. Bland–Altman analysis revealed an average bias of 0.89 mm2, and a variance (1 SD) of 4.16 mm2 (95% CI: −7.43–9.21).
The intraclass correlation coefficient was 0.96, and intraobserver variability was 14.8 ± 13.5%. Bland–Altman analysis revealed an average bias of 0.98 mm2, and a variance (1 SD) of 3.84 mm2 (95% CI: −6.70–8.66).
We demonstrated that 2DVCA correlates with 3DVCA and EROA. Three-dimensional echocardiographic imaging facilitates direct measurement of VCA [9-14]. Using 2D echocardiography in the 2D parasternal short-axis view, VCA can be overestimated if the imaging plane is below the vena contracta (expanding portion of the jet spray), above the aortic valve (proximal flow convergence), or if perpendicular imaging plane alignment is inadequate. When measuring 2DVCA using conventional 2D color Doppler imaging, there are two major considerations. First, 2DVCA measurement must be performed at the level of the vena contracta. We primarily measured 2DVCA using the parasternal approach. We were careful to measure the cross-sectional plane of the vena contracta—the narrowest area of the jet—and not the cross-sectional planes of the proximal flow convergence or distal expansion of the regurgitant jet spray during mid-diastole (Figure 1). If the flow convergence is visible in the short-axis view, the area upstream of the vena contracta, part of the proximal isovelocity surface area, is being imaged. On the contrary, the downstream area of the AR jet is bigger than the vena contracta. For reference, we attempted to describe the complete AR jet using the long-axis view, then calculate VCA by measuring the smallest area between the proximal flow convergence and distal regurgitant jet spray in the short-axis view. It is important to begin the 2D scan at the proximal flow convergence, moving the image plane toward the regurgitant jet spray to identify the smallest area of the vena contracta.
In this study, interobserver and intraobserver variability were low and the intraclass correlation coefficient was good. To our knowledge, this is the first study to show that 2DVCA can evaluate AR severity as well as 3DVCA. Measurement of 2DVCA is a simple technique, feasible for use clinically at patients’ bedsides or in the emergency room, during comprehensive Doppler echocardiographic AR severity assessment. VCA can be measured simply by calculating the shape of regurgitant orifice as an ellipse, using the major (VCW1) and minor (VCW2) axis of the regurgitant flow, two orthogonal VCW: VCA = π × (VCW1) × (VCW2)/4 = 0.785 × (VCW1) × (VCW2), and this method may have a potential role as simple semiquantitative assessment of AR severity in patients with eccentric AR.
In this study, no patient exhibited multiple regurgitant orifices or prosthetic paravalvular regurgitation; thus, we cannot extrapolate our results to such patients. In a recent study , 3DVCA was reported to be a useful technique in such patients, and further studies of 2DVCA are justified. For the clinical study, we chose Doppler-derived EROA as the independent reference standard. Further studies comparing 2DVCA with magnetic resonance imaging may provide insight for assessing AR severity. The number of patients enrolled, especially those with severe AR, was small. Further studies are necessary to definitively validate this method.
Significant correlation existed between 2DVCA and 3DVCA as well as between 2DVCA and ERO, RV, and VCW. Measurement of 2DVCA is a simple technique for clinical use during comprehensive Doppler echocardiographic assessment of AR severity.
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