The narrowest portion of the color flow signal just beyond the valve leaflets is referred to as the vena contracta. The measurement of the vena contracta width is less influenced by technical factors and is done perpendicular to its long axis. For better visualization, the sector should be narrowed and the depth decreased. The AR jet crossing the AV is then interrogated at its narrowest point, which in the case of multiple or eccentric jets can be difficult or impossible. Often the vena contracta does not have a perfectly round shape, and thus measuring its width in an orthogonal plane can introduce error. Three-dimensional echocardiography, particularly simultaneous orthogonal imaging, can be a very useful addition to accurately delineate the narrowest portion of the regurgitant jet (Fig. 5). A vena contracta width of >0.6 cm is consistent with severe AR (Table 1).9 In one study comparing several semiquantitative echocardiographic methods, the vena contracta appeared to be the most sensitive method to assess AR severity.10
The proximal isovelocity surface area method is a combination of color and spectral Doppler methods to measure the EROA of a regurgitant valve. In the case of AR, there is little clinical experience with this method when compared with mitral regurgitation and even less using TEE. The technique becomes problematic and potentially inaccurate when a proximal isovelocity surface area region is not hemispheric because of poor visualization or in cases of eccentric or multiple AR jets.
Pulsed Wave Doppler
The assessment of flow in the descending thoracic aorta by pulsed wave (PW) Doppler can provide an indirect, but important qualitative sign of severe AR. The descending thoracic aorta should be visualized in a long-axis view with the PW Doppler sample volume directed distally toward the abdominal aorta. To allow adequate Doppler beam alignment, the multiplane angle may need to be adjusted accordingly. A small amount of retrograde diastolic flow is physiologic, particularly in older age with decreasing aortic compliance. However, increasing velocity and duration of diastolic flow reversal correlates with increasing AR severity.11 Holodiastolic flow reversal is a sign of at least moderate AR and becomes more specific when recorded further distally in the descending thoracic aorta (Fig. 6). Alternatively, the velocity or the velocity time integral (VTI) of the reversal flow can be measured. An end-diastolic velocity of >10 to 15 cm/s or a diastolic VTI that is equal to the VTI of antegrade flow is consistent with severe AR.11
PW Doppler can be used to measure the regurgitant volume (RVAR) or regurgitant fraction (RFAR) of the AR jet. This is accomplished by comparing flow through the regurgitant AV with flow through a competent valve, often the pulmonic valve. Stroke volumes (SVs) are calculated by using the CSA multiplied by the VTI. For the LV, the SV is derived from the LVOT; for the right ventricle (RV), the SV is measured in the right ventricular outflow tract in a similar fashion using PW Doppler. Because flow rate or SV through a regurgitant valve is larger than through a competent valve, the difference between the 2 equals the RVAR:
Because this method uses flow across the right ventricular outflow tract, the degree of pulmonic regurgitation should not exceed mild. Continuing from here, the EROA can be calculated using the RVAR and the VTIAR (the VTIAR is obtained by tracing the continuous flow Doppler profile of the AR jet from a TG echocardiographic window):
Common problems with this technique are inaccurate annular measurements for calculation of the CSA to derive the SV and inadequate PW Doppler beam alignment.12
Continuous Flow Doppler
A simple yet rough measure to estimate AR severity is the density of the AR jet by continuous wave (CW) Doppler echocardiography. Color Doppler can be of help to accurately align the CW Doppler beam with the AR jet, especially if jets are eccentric. Eccentric jets are particularly challenging and may not be amenable to accurate CW Doppler interrogation. Unless the AR jet is imaged properly and the CW signal shows a trapezoidal shape with flow velocities of 3 to 4 m/s, any CW Doppler-based measurement will likely be inaccurate (Fig. 7).
The slope of the CW signal can give information on both severity and chronicity of AR. The diastolic pressure difference between the LV and the aorta equalizes more rapidly in the setting of severe AR that results in a steeper slope of the CW signal (Fig. 7). The pressure half-time (PHT) is defined as the time it takes for the transvalvular pressure gradient to decrease by 50% starting from its maximum. A PHT of <200 milliseconds reflects severe AR, a PHT >500 milliseconds generally indicates mild AR, whereas intermediate values are difficult to interpret and less helpful in delineating severity and progression (Table 1). In the case of chronic AR and LV adaptation to the volume overload, the CW slope will be less steep and PHT thresholds become less reliable.13
Because many of the methods described earlier have intrinsic limitations, it is advised to look at the assessment results derived from different views and different echocardiographic modalities. An example is the 3D shape and variable direction of AR jets in conjunction with the geometrical complexity of the LVOT and aortic root. For this diagnostic conundrum, 3D echocardiography is a very promising modality.14 The morphology of the AV complex can be assessed using real-time, real-time zoomed, or electrocardiogram-gated 3D imaging (Video 5, Supplemental Digital Content 5, http://links.lww.com/AA/B249). Once acquired, the 3D data set can be magnified, rotated, and cropped to complete the anatomic image of the AV complex. Color Doppler can be added rendering a 3D model of AR that can provide valuable information regarding number, origin, direction, and extension of regurgitant jets (Fig. 8, Video 6, Supplemental Digital Content 6, http://links.lww.com/AA/B250). As mentioned earlier, simultaneous orthogonal imaging can be helpful in the assessment of AR jets. Two-dimensional echocardiography-derived measurements of vena contracta or jet width assume a round or ellipsoid AR jet. However, studies using 3D echocardiography showed that this is often not the case and that multiplanar reconstruction of gated 3D color data sets can accurately measure vena contracta widths or areas that correlate with AR severity.15 Limitations of 3D echocardiography include artifacts related to motion, respiration, and arrhythmias, which is of particular importance in multibeat acquisitions. However, real-time 3D echocardiography and single-beat image acquisition can eliminate some of those artifacts but have other limitations, such as relatively low frame rates. Dropout artifacts are common, especially with thin valves, like the AV, and acoustic shadowing from calcifications is equally a challenge in 3D as it is in 2D echocardiography. Again, 3D color imaging is a promising additive to enhance understanding and measurement of complex AR jets; however, some aspects require further clinical validation, particularly when using TEE.
- Two-dimensional echocardiography is used to assess aortic valve and root anatomy, particularly cusp number, mobility, and dimensions. Together with the assessment of left ventricular size and function, this information can help identify the etiology and mechanism of regurgitation.
- Color Doppler echocardiography is a simple method to evaluate the presence, shape, direction, number, and dimension of aortic regurgitation jets. Measurement of the vena contracta width appears to be the most sensitive color Doppler method to assess the degree of regurgitation. Simultaneous orthogonal imaging can add accuracy to the vena contracta assessment, particularly in the setting of complex regurgitant jet morphology.
- Regurgitant volume and regurgitant fraction are quantitative measures of aortic regurgitation and are calculated comparing flow through a regurgitant valve with flow through a competent valve using pulsed wave Doppler. Holodiastolic flow reversal in the descending thoracic aorta can be indicative of severe aortic regurgitation.
- Pressure half-time is derived from the deceleration slope of an aortic regurgitation jet using continuous flow Doppler. A steep slope results in a short pressure half-time and indicates severe aortic regurgitation.
- Because most methods of quantification have intrinsic limitations because of poor signal quality, loading conditions, and echo windows, it is important to combine different independent indices as well as clinical status to formulate a diagnosis. Three-dimensional echocardiography can provide important morphologic information, and 3D color techniques can improve the quality of regurgitant jet assessment.
Name: Peter von Homeyer, MD, FASE.
Contribution: This author helped design the study and prepare the manuscript.
Attestation: Peter von Homeyer approved the final manuscript.
Name: Donald C. Oxorn, MD, CM, FRCPC, FACC.
Contribution: This author helped design the study and prepare the manuscript.
Attestation: Donald C. Oxorn approved the final manuscript.
This manuscript was handled by: Martin J. London, MD.
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