Version May 2024
INTRODUCTION — Echocardiography is the procedure of choice for the evaluation of valvular heart disease. Because of enhanced resolution and unobstructed visualization, transesophageal echocardiography (TEE) may provide further detail not obvious on transthoracic echocardiography (TTE) and may facilitate direct planimetric measurements of the valve orifice. TEE also has a growing role in transcatheter aortic valve implantation (TAVI).
This topic will discuss TEE evaluation of the aortic valve. TTE evaluation of the aortic valve is discussed separately. (See "Echocardiographic evaluation of the aortic valve".)
MORPHOLOGY — To characterize the aortic valve using TEE, the valve should be imaged in short- and long-axis views with and without color flow Doppler.
Short-axis view — The short axis of the aortic valve can generally be visualized in a plane between 30 to 60° from the transverse (0°) using a multiplane transducer [1]. In the short-axis view, inspection should include identification of the number of aortic cusps, the presence and extent of calcification, fusion, leaflet perforation, malcoaptation, or vegetation. Adjustment of the imaging plane to a view that clearly demonstrates the coaptation of the leaflets provides another view for regurgitant jet assessment. Direct planimetry of the stenotic systolic orifice from this view is accurate to a level that equals, and may exceed, that of the standard continuity equation as applied to Doppler TTE. (See 'Aortic stenosis' below.)
Long-axis view — In the long-axis view, typically at 110 to 140° from transverse (0°) [1], the right and noncoronary cusps are visualized and the presence of any vegetations or leaflet prolapse is usually evident and regurgitant jet width can be ascertained. In the long axis, the ascending aorta should be viewed from the valve to the right pulmonary artery. This view of the left ventricular outflow tract (LVOT) is usually optimal for excluding subvalvular lesions (eg, subvalvular membrane), measuring regurgitant jet width and for examining associated pathology of the aortic valve, aortic root, and ascending aorta (eg, annuloaortic ectasia, type I aortic dissection, and Marfan syndrome).
Two-dimensional simultaneous mode and three-dimensional echocardiography — Current matrix array transducers permit 360° rotation of the imaging plane and can facilitate identification of short-axis images of the aortic valve. Display of the long- and short-axis views can also occur simultaneously. Moreover, both real-time three-dimensional imaging and ECG-gated acquisitions can be performed, which can be extremely helpful in guiding transcutaneous aortic valve implantation when transthoracic imaging is limited [2].
Three-dimensional (3D) TEE is increasingly utilized in the evaluation of valvular disorders. With this modality, the internal contour of the valvular surface can be visualized (termed "en face" visualization). In a single-center study, the ability to identify leaflet perforation was compared between 3D TEE and two-dimensional (2D) TEE. 3D and 2D TEEs on patients with known perforated native valves were collected and combined with 3D and 2D TEEs from patients with endocarditis. Of the 14 patients with known valve perforations, 15 perforations were diagnosed on 3D TEE (seven involving the aortic valve) versus 11 perforations (six involving the aortic valve) diagnosed on 2D TEE. 3D TEE was also associated with higher level of confidence in diagnosis [3]. Another study demonstrated greater sensitivity in detecting Libman-Sacks vegetations in patients with lupus with 3D TEE compared with 2D TEE [4].
Identification of etiology of disease — The etiology of aortic valve disease and associated conditions can often be better delineated by TEE than transthoracic echocardiography (movie 1).
●Cause of AR – Patients with an intrinsically normal valve who have aortic regurgitation (AR) due to a correctable aortic lesion (aortic root dilation causing incomplete leaflet closure or dissection flap prolapse) are candidates for aortic valve repair. In contrast, irreparable valve abnormalities (eg, retracted calcified valve) require valve replacement. Causes of aortic valve disease are discussed separately. (See "Echocardiographic evaluation of the aortic valve" and "Clinical manifestations and diagnosis of aortic stenosis in adults" and "Clinical manifestations and diagnosis of chronic aortic regurgitation in adults" and "Acute aortic regurgitation in adults".)
In a study of patients undergoing surgery for AR, lesions were visualized preoperatively on TEE and classified into three categories: root dilation, excess cusp motion, or deficient cusp quality or quantity. There was 93 percent agreement between the causal classification of regurgitation by TEE with that determined by surgical inspection [5].
●Bicuspid aortic valve – Congenital bicuspid aortic valve is associated with development of stenosis and/or regurgitation and dilatation of the aortic root [6]. This dilatation is thought to be due to abnormalities of the aortic media, as opposed to being the sequelae of increased velocities through a stenotic bicuspid valve [6,7]. An increased incidence of aortic dissection has also been reported in patients with bicuspid aortic valve [8]. Thus, in patients with bicuspid aortic valve undergoing TEE, we recommend careful examination for associated pathology of the aortic root and ascending aorta. (See "Clinical manifestations and diagnosis of bicuspid aortic valve in adults".)
●Subaortic stenosis – Rarely, LVOT obstruction may be caused by a discrete fibrous subaortic membrane, not visualized on TTE. TEE provides excellent delineation of this pathology and may detect associated AR that occurs due to gradual valvular degeneration caused by the impact of the high velocity jet associated with subaortic stenosis.
●Aortic dissection – TEE views can also define the severity and mechanism of AR that complicates acute type A aortic dissection [9]. (See "Acute aortic regurgitation in adults" and "Clinical features and diagnosis of acute aortic dissection".)
●Vegetations – TEE is also important for detecting aortic valve vegetations in patients with suspected endocarditis. Other masses, such as papillary fibroelastomas and Lambl excrescences, may be found only on TEE. Papillary fibroelastomas may be found incidentally or when a patient presents with cerebral ischemia. Rarely, they can prolapse into a coronary orifice and cause myocardial ischemia. Lambl excrescences are smaller strands and part of a degenerative process. (See "Cardiac tumors", section on 'Papillary fibroelastomas' and 'Two-dimensional simultaneous mode and three-dimensional echocardiography' above.)
GRADING HEMODYNAMIC SIGNIFICANCE
While TEE is rarely the primary diagnostic modality for evaluating the severity of aortic valve disease, it is useful in patients with suboptimal TTE and in patients with conflicting data among various noninvasive modalities. As TEE is used intraoperatively in patients undergoing aortic valve surgery, either repair or replacement, as well as during percutaneous aortic valve replacement, it is important to understand the strengths and limitations of TEE in grading the hemodynamic significance of the disease. Additionally, patients undergoing TEE during cardiac surgery for coronary disease or other valve disease should be evaluated for the presence of previously undiagnosed aortic valve lesions.
Aortic stenosis — Transthoracic Doppler echocardiography is an established method for determining the severity of aortic stenosis (table 1) [10] (see "Echocardiographic evaluation of the aortic valve" and "Clinical manifestations and diagnosis of aortic stenosis in adults"). Doppler determination of severity is less successful on TEE as it is difficult to achieve beam alignment to measure the maximal flow velocity across the valve (in some cases, the deep trans-gastric view on TEE can be utilized to obtain accurate velocities). However, the resolution on transthoracic echocardiography may not permit direct planimetry of a stenotic aortic valve, while TEE generally obtains better images of the stenotic orifice.
In one study of stenotic valves, the correlation coefficient for valve area computed by planimetry on TEE and by continuity equation on TTE was 0.93, the percent difference between the two methods was small (11 percent), and the TEE method correlated even more closely with the catheterization-determined valve area (using the Gorlin formula) than did the transthoracic echocardiographic value (r = 0.91 versus 0.84) [11] (see "Aortic valve area in aortic stenosis in adults"). Planimetry by TEE has also been shown to correlate well with planimetry by computed tomography [12]. However, a study using 3D echocardiography in patients with calcific aortic stenosis showed that the valve area was underestimated when compared with valve area measurements by the continuity equation using transthoracic echocardiography, suggesting that heavy calcification limits direct planimetered measurements of the orifice [13].
Aortic regurgitation — Transthoracic Doppler echocardiography methods for grading the severity of aortic regurgitation (AR) include use of continuous-wave Doppler imaging of the regurgitant jet [14], pulsed-wave Doppler imaging of reverse flow in the descending aorta [15], and color flow Doppler imaging of the width of the regurgitant jet in the left ventricular outflow tract (LVOT) [16] and the vena contracta; these methods are reliable and complementary [17]. (See "Echocardiographic evaluation of the aortic valve".)
TEE is rarely needed to evaluate severity of AR and is generally limited to patients with poor transthoracic acoustic windows. There are scant data on the comparative value of TEE and TTE in measuring the severity of AR (image 1). In patients with limited acoustic windows, the severity of AR may be best evaluated by combining available data from transthoracic echocardiography and TEE. Using either modality it is important to evaluate mitral inflow and regurgitant flows to determine whether severe AR is causing elevated filling pressures resulting in restricted mitral inflow or diastolic mitral regurgitation.
TEE generally visualizes the LVOT well and is highly sensitive to even trivial degrees of regurgitation (movie 2). The vena contracta is the narrowest portion of the color flow jet as it leaves the aortic valve and enters the LVOT (receiving chamber). The width of the vena contracta (as well as the jet width in the LVOT just below the vena contracta) correlates with the severity of AR. A vena contracta width of <0.3 cm is considered mild and >0.6 cm as severe with intermediate values judged moderate [18]. One study found that the width and area of the vena contracta measured from TEE correlated well with the regurgitant fraction and regurgitant volume as measured with a flow probe at the time of surgery [19]. Another parameter of AR severity is the jet width/LVOT diameter with a value >65 percent being severe and <25 percent being mild; this parameter is more difficult to accurately measure in the presence of an eccentric jet.
Since TEE views are generally suboptimal for measuring continuous-wave Doppler signals of the AR jet or pulsed-wave Doppler of flow reversal in the descending aorta, TTE is generally preferred for evaluation of these variables. However, flow reversal in the descending aorta can also be identified by TEE [20]. Descending aorta flow reversal may be the only way to assess AR by TEE in patients with a mitral valve prosthesis in whom the LVOT cannot be adequately visualized. We have found that the descending aorta viewed in the long axis provides the most nearly axial Doppler angle obtainable from TEE. From this vantage, flow reversal associated with moderate and severe AR is most reliably and accurately seen.
TEE is also very helpful in elucidating the mechanism of AR. The following classification has been proposed and is based on the Carpentier classification for mitral regurgitation. Type I lesions have normal aortic cusp motion with either a dilated annulus or cusp perforation. In type II lesions, there is leaflet prolapse, and in type III, there is restricted diastolic closure of the leaflets. The mechanism of AR may have implications for the surgical management.
INTRAOPERATIVE — TEE is frequently used intraoperatively, and it has the potential to guide aortic valve surgery and improve outcomes. Prior to aortic valve replacement or repair, valvular pathology can be examined and final annular measurements can be obtained for correct prosthesis sizing. In the patient with endocarditis, careful inspection of the aortic root may reveal ring abscess that requires debridement. After the procedure is complete, prosthesis seating can be directly observed and color flow Doppler can detect perivalvular regurgitation. Multiplane mapping (particularly long-axis views) enables identification of the extent of any paravalvular leaks, which may need to be addressed prior to chest closure. When aortic valve repair is performed, TEE evaluation of valve function post-repair is essential [21].
A pooled analysis examined the impact of intraoperative TEE on surgeries for valvular heart disease. Eight observational studies with a total 15,540 patients were included in the study. TEE done intraoperatively prior to cardiopulmonary bypass resulted in changes to the planned surgical procedure 11 percent of the time. TEE findings resulting in alteration to the surgical plan included complications of endocarditis, left ventricular outflow tract obstruction, and measurement of the aortic annulus for homograft sizing. There was a 4 percent incidence of second pump runs based on residual valvular abnormalities seen on post-cardiopulmonary bypass intraoperative TEE [22].
In patients undergoing transcutaneous aortic valve replacement, intraprocedural TEE is now widely used [23]. The roles of TEE are: to size the valve through measurements of the annular area, to ensure proper positioning of the valve, to provide rapid detection of intraprocedural complications, and to evaluate for periprosthetic leak. The major disadvantage of TEE is that it requires that the patient be intubated and for that reason, some centers are now performing transthoracic echocardiography to guide the procedure. (See "Imaging for transcatheter aortic valve implantation", section on 'Imaging during transcatheter heart valve implantation'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Cardiac valve disease".)
SUMMARY AND RECOMMENDATIONS
●Use of TEE for aortic disease – The etiology of aortic valve disease and associated conditions can often be better delineated by transesophageal echocardiography (TEE) than transthoracic echocardiography (TTE). Newer modalities such as three-dimensional (3D) TEE have strengthened this diagnostic potential. (See 'Morphology' above.)
•For subvalvular and aortic pathology – TEE provides detail of the aortic root and the ascending aorta that can be helpful in excluding subvalvular and aortic pathologies. Given the association with dilatation of the aortic root, patients with congenital bicuspid aortic valves undergoing TEE should have careful examination of the aortic root and ascending aorta. (See 'Identification of etiology of disease' above.)
•Cause of aortic regurgitation – TEE can elucidate the mechanism for aortic regurgitation (AR), and this information can be critical in planning for repair of the valve. (See 'Identification of etiology of disease' above.)
●Adjunctive roles – While TTE is generally the first line diagnostic technique in aortic stenosis or regurgitation, TEE should be considered as an adjunct to TTE in the following circumstances:
•When there are conflicting data from invasive and noninvasive studies as to the hemodynamic severity of AR or stenosis.
•When coexistent aortic valve disease needs to be excluded in a patient undergoing coronary artery bypass graft or other intracardiac repairs.
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Amy L Gin, MD, who contributed to earlier versions of this topic review.
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