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Aortic Regurgitation

Echocardiographic Diagnosis

von Homeyer, Peter MD, FASE; Oxorn, Donald C. MD, CM, FRCPC, FACC

doi: 10.1213/ANE.0000000000001013
Cardiovascular Anesthesiology: Echo Didactics
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SDC

From the Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, Washington.

Accepted for publication August 18, 2015.

Funding: None.

The authors declare no conflicts of interest.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s website.

Reprints will not be available from the authors.

Address correspondence to Peter von Homeyer, MD, FASE, Department of Anesthesiology and Pain Medicine, University of Washington, 1959 NE Pacific St., Box 356540, Seattle, WA 98195. Address e-mail to peter2@uw.edu.

A 69-year-old man with hypertension is admitted to the emergency room with sudden onset of chest and back pain. A computed tomography scan of his chest shows a dissection of his ascending aorta, for which he is taken to the operating room in an urgent manner. The intraoperative transesophageal echocardiogram (TEE) shows normal left ventricular (LV) function and a dissection flap in the proximal ascending aorta. Aortic regurgitation (AR) is noted, and a request to assess the AR severity is made by the surgical team.

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BACKGROUND

The aortic valve (AV), the sinuses of Valsalva, and the sinotubular junction form a functional anatomical unit, described as the aortic root. The AV features 3 semilunar cusps, the left, right, and the noncoronary cusps. Unlike the atrioventricular valves, the AV has no distinct fibrous annulus. Instead, the LV outflow tract (LVOT) has an “uneven” area of fibrous tissue, a transition zone from ventricular muscle to typical arterial wall, which is commonly referred to as the AV annulus.1

AR is caused by either intrinsic valvular disease or disorders affecting the aortic root and ascending aorta.2 Aside from calcific AV disease, other common etiologies for intrinsic valvular disease leading to AR are bicuspid AV, rheumatic heart disease, and infective endocarditis.3 If not caused by intrinsic valvular disease, AR is often secondary to aneurysmal dilation of the aortic root or type A aortic dissections.4 In summary, mechanisms of AR can be divided into 3 general categories, leaflet prolapse, leaflet restriction, and root dilation with usually normal leaflet motion. Leaflet perforation is a less common but important cause of AR in the setting of normal leaflet motion. Identifying those mechanisms can have an impact on decision making regarding possible repair strategies versus valve replacement.5

Clinically, patients with AR may present as critically ill, with pulmonary edema from acute left heart failure in cases of acute-onset regurgitation or rather stable within the setting of chronic AR, a slowly progressive disease.

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ECHOCARDIOGRAPHIC IMAGE ACQUISITION

Starting from a midesophageal (ME) 4-chamber view, the ME AV short-axis view is obtained by rotating the multiplane angle to 30° to 50°. Slight advancement or withdrawal and turning the TEE probe to the patient’s right bring all 3 cusps into view. Rotating the multiplane angle to 120° for the ME AV long-axis view images the LVOT and, with slight probe withdrawal, the entire aortic root. In this view, the right coronary cusp of the AV is seen anteriorly (farther away from the probe). The cusp often seen posteriorly (closer to the probe) is either the noncoronary cusp or the left coronary cusp, whereas in theory this view should cut directly through the commissure between these 2 cusps, and no cusp should be visible in systole. Color Doppler can be applied in both ME views to visualize AR and to describe the characteristics of AR jets. Three-dimensional echocardiography techniques including simultaneous orthogonal imaging can help to further assess morphology of the AV complex and AR jets.

The TEE probe is then further advanced to obtain transgastric (TG) views. Either a deep TG long-axis view with the multiplane angle at 0° to 30° or a TG long-axis view with the multiplane angle rotated to approximately 120° can be used. TG TEE views are essential for the quantitative assessment of AR because they allow for adequate Doppler beam alignment with blood flow through the AV. Color Doppler echocardiography visualizes AR, then spectral Doppler is used to further interrogate the regurgitant jet. When using Doppler, beware of mistaking the normal LV inflow signal for a jet of AR because both these jets occur in diastole; AR jets tend to have a higher velocity and show more turbulence than the LV inflow signal. Finally, the TG mid-short-axis view at 0° is the appropriate view to assess LV chamber size.6,7

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2D ECHOCARDIOGRAPHY

The initial qualitative assessment provides information on AV cusp number and appearance, degree of calcification, and possible vegetations or paravalvular abscess formation (Fig. 1; Video 1, Supplemental Digital Content 1, http://links.lww.com/AA/B245). When shifting to the long-axis view, potential findings can be substantiated. AV cusp motion and mobility can be assessed in this imaging plane, and potential cusp prolapse can be diagnosed (Fig. 2; Video 2, Supplemental Digital Content 2, http://links.lww.com/AA/B246).

Figure 1

Figure 1

Figure 2

Figure 2

The ME AV long-axis view is also the appropriate echocardiographic window to best assess pathologies of the aortic root such as aneurysmal dilation or dissections (Fig. 3; Video 3, Supplemental Digital Content 3, http://links.lww.com/AA/B247). Also in this view, AV annular and other aortic diameters can be measured. These are potentially important measurements because dilation, for example, of the sinotubular junction can lead to incomplete AV leaflet closure and subsequent AR. This area of noncoaptation is also well visualized in an ME AV short-axis view. However, dissection flaps in the ascending aorta can best be identified in the ME AV long-axis view. These can be the cause of AR by either tethering of one or more AV cusps or by flap prolapse through the AV into the LVOT.

Figure 3

Figure 3

Finally, a thorough assessment of LV dimensions, mass, and systolic function should be part of any 2D examination in patients with AR.7 This does not only have prognostic relevance and impacts clinical management but can give useful information on the chronicity of AR. In chronic AR, the LV has usually dilated over time as a result of the increased end-diastolic volume. In acute AR on the contrary, patients generally have a normal size LV, and because of the acute rise in afterload and the subsequent increase in LV wall stress, this valvular lesion is poorly tolerated and often needs immediate surgical repair.

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DOPPLER ECHOCARDIOGRAPHY

Color Flow Doppler

Application of color Doppler at the level of the AV in an ME AV short-axis view is a fast and simple method to assess presence, size, and location of a regurgitant jet or possibly more than one jet. Rotating the multiplane angle to approximately 120° to an ME AV long-axis view will help to interrogate the flow through the LVOT, AV, and ascending aorta. In this view, ideally all 3 zones of the AR complex should be seen, the flow convergence zone above the AV, the narrowest portion of the jet or vena contracta, and the extension of color flow into the LVOT. As a general principle, the short-axis view is preferred to describe AR jet origin and the long-axis view to describe AR jet direction.

The depth of penetration of the AR jet into the LV cavity was traditionally used but proved to be an inaccurate measure of severity. This technique is limited by the fact that jet characteristics are influenced not only by the effective regurgitant orifice area (EROA) but also by the balance between LV and aortic compliance. More commonly, the AR jet is mapped at its widest diameter, but no more than 1 cm below the AV.8 For quantification purposes, this width can be put in relation to the LVOT diameter in the same location, and a ratio of >0.65 is consistent with severe AR (Table 1). Alternatively, the cross-sectional area (CSA) can be calculated from the jet width and then used in a ratio to the LVOT area. AR jet interrogation by color Doppler has limitations because of the 3D nature of AR jets and the LVOT. Thus, elliptical, eccentric, and multiple AR jets are poorly assessed by this method. Three-dimensional echocardiography can be a helpful addition in these cases because it accounts for some of the geometric complexity of the AV complex. It is useful to better describe origin and direction of AR jets and for the measurement of jet width and area. Eccentric jets often deflect at the anterior leaflet of the mitral valve, causing a characteristic fluttering of this leaflet (Fig. 4; Video 4, Supplemental Digital Content 4, http://links.lww.com/AA/B248). Severe acute AR and the associated rapid rise in LV pressure during diastole often lead to premature closure of the mitral valve or even diastolic mitral regurgitation in severe cases.

Table 1

Table 1

Figure 4

Figure 4

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

Figure 5

Figure 5

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.

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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

Figure 6

Figure 6

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

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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).

Figure 7

Figure 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

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FUTURE DIRECTIONS

Figure 8

Figure 8

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.

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Teaching Points

  • 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.
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DISCLOSURES

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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