Transesophageal echocardiography in the evaluation of mitral valve disease

INTRODUCTION — While transthoracic echocardiography (TTE) is the primary diagnostic modality for evaluation of mitral disease, transesophageal echocardiography (TEE) is an important adjunct in selected patients when more detailed visualization of the mitral valve morphology and of the left atrium (eg, to identify atrial thrombus) is needed.

This topic will discuss the use of TEE in evaluating the mitral valve. TTE of the mitral valve is discussed separately. (See "Echocardiographic evaluation of the mitral valve".)

MITRAL REGURGITATION — Mitral regurgitation (MR) is one of the most common derangements of native valves and increases in frequency with age. MR is broadly classified as primary, related to structural abnormalities of the valve itself, or secondary, due to impaired leaflet coaptation associated with underlying left ventricular (LV) disease or left atrial disease. Defining the morphology of the valve (figure 1) and the precise mechanism of regurgitation has gained importance in the modern era of surgical and percutaneous mitral valve repair.

The important role TEE plays in the evaluation of MR is due to the proximity of the TEE transducer to the left atrium. In situations that impede TTE (eg, acoustic shadowing from annular calcium or a mitral prosthesis), TEE provides an unobstructed view. TEE provides enhanced views of the mitral valve, which now include three-dimensional (3D) reconstruction to provide detailed information as to the nature of the underlying pathology. The TEE also provides information that is adjunctive to the TTE in determining the severity.

Primary mitral regurgitation — As noted in the American College of Cardiology/American Heart Association (ACC/AHA) guidelines, TEE is indicated in evaluation of patients with chronic primary MR (stages B to D) (table 1) in whom noninvasive imaging provides nondiagnostic information about severity of MR, mechanism of MR, and/or status of LV function [1]. TEE may provide significant additional information in the following conditions that lead to chronic MR.

Degenerative mitral valve disease — This condition is the most common cause of primary mitral valve regurgitation. In most cases, the leaflets are thickened and redundant. It is usually an isolated condition but may also occur as a feature of disorders such as Marfan syndrome or Ehlers-Danlos syndrome. Prolapse may involve one or more of the three scallops of the posterior leaflet, the anterior leaflet, or both leaflets. (See "Mitral valve prolapse: Clinical manifestations and diagnosis".) Mitral valve prolapse also occurs with relatively normal leaflets.

The most common mechanical complication of mitral valve prolapse is ruptured chordae tendineae, which can result in acute and often severe MR. On TTE, the condition usually can be diagnosed by observing a flail portion of the mitral valve protruding into the left atrium in systole. A remnant of the severed chord can often be seen as a filamentous structure, moving with the flail portion of the leaflet. At times, it can be difficult to differentiate between the flail portion of the leaflet and a vegetation, although the appearance of the mass and the clinical setting usually aid diagnosis. (See "Mitral valve prolapse: Overview of complications and their management".)

TEE is also more precise than TTE in determining the precise location of the flail leaflet, specifically which of the three scallops of the leaflet is involved. The middle scallop of the posterior leaflet (P2) is the most common site of chordal rupture. This information is important in planning mitral valve repair. 3D TEE has provided greater specificity in localization of the pathology [2,3].

Rheumatic disease — Postinflammatory (ie, rheumatic) changes in the mitral valve are recognized by the same features in both TEE and TTE. Valve thickening, immobility, doming into the ventricle, chordal foreshortening, and calcification support this diagnosis. Usually, there is mixed mitral regurgitation and stenosis. MR in this condition is characterized by restricted leaflet motion leading to malcoaptation. (See "Echocardiographic evaluation of the mitral valve".)

Valve lesions related to systemic lupus erythematosus have been related to antiphospholipid antibodies, but this association is controversial; antiphospholipid antibodies can also occur in patients without lupus [4]. These lesions cause focal areas of thickening, which concentrate on the atrial aspect of the valve toward the tips of the leaflets, creating a club-like appearance. Occasionally, the lesions are associated with severe MR. (See "Non-coronary cardiac manifestations of systemic lupus erythematosus in adults".)

Congenital abnormalities — The most common congenital etiology of MR encountered in the adult is a partial or previously repaired complete atrioventricular septal defect (also known as endocardial cushion defect). The bridging anterior and inferior leaflets appear "cleft" and are frequently incompetent. TEE may be useful in defining both the site of regurgitation and the presence of residual septal defects. Other congenital causes of MR include the isolated cleft mitral valve and mitral valve fenestrations.

Infective endocarditis — A common acquired cause of MR is endocarditis, either complicating an underlying valve lesion (eg, mitral valve prolapse with regurgitation) or causing primary destruction of a normal mitral valve, usually in the presence of a virulent organism such as Staphylococcus aureus. (See "Complications and outcome of infective endocarditis".) The mechanisms for MR in endocarditis include [5]:

●Primary leaflet destruction

●Leaflet perforation

●Chordal rupture

●Papillary muscle rupture (rarely) [5]

TEE not only has superior sensitivity in identifying vegetations and elucidating the mechanism for valve dysfunction, but also in detecting the presence of a perivalvular abscess (image 1 and image 2), which can involve the mitral annulus. A meta-analysis suggested that a high-quality TTE has a strong negative predictive value for the presence of vegetations if there is no more than trace valvular regurgitation and no structural abnormalities of the valve [6]. TEE should be reserved for patients with indeterminate TTE and in cases where management would be altered by the findings.

In most cases, vegetations are found on the atrial aspect of the leaflets or on the leaflet tips. When there is secondary involvement of the mitral valve in patients with aortic valve endocarditis, vegetations can be visualized on the ventricular aspect of the anterior leaflet where the aortic regurgitation jet is directed; often, the valve perforates at this site. Studies using 3D TEE have demonstrated the utility of this method in identifying the mechanism for MR in the setting of endocarditis [7]. 3D TEE has been shown to have greater sensitivity for detecting these non-bacterial vegetations on the mitral valve [8]. (See "Role of echocardiography in infective endocarditis".)

Marantic or nonbacterial endocarditis is most often associated with systemic lupus erythematosus, but is also seen in the antiphospholipid syndrome [4,9]. The typical lesion is characterized by focal areas of thickening concentrated on the atrial aspect of the valve toward the tips of the leaflets. These vegetations are usually sessile. Occasionally, severe MR is associated with these lesions. 3D echocardiography has been shown to improve sensitivity for detection of Libman-Sacks vegetations in patients with SLE [8]. (See "Clinical manifestations of antiphospholipid syndrome".)

Degenerative calcific disease — Older adult patients with severe degenerative calcific mitral valve disease infrequently have severe MR, occasionally due to ruptured chordae tendineae. Calcification often obscures the presence of MR on surface Doppler imaging because of acoustic "shadowing" in the posteriorly located left atrium. TEE may be necessary to confirm the presence of MR in this condition, which can also cause hemodynamically significant mitral stenosis (MS) in older adults.

Secondary mitral regurgitation — Functional MR can be inferred when the valve is morphologically normal but the LV is either globally or segmentally abnormal. The papillary muscles are splayed or displaced, leading to leaflet tethering, which can be symmetric or asymmetric. With symmetric tethering, as seen with global dysfunction, the color flow jet is usually central, occurring at a coaptation point that is marked by decreased contact area and displacement toward the LV apex. With regional wall motion abnormalities, there may be asymmetric tethering leading to eccentric jets (eg, with ischemic MR). The role of TEE in the assessment of secondary MR is less well established. Exceptions include the diagnosis of papillary muscle rupture in myocardial infarction and chordal rupture associated with hypertrophic cardiomyopathy.

Ischemic mitral regurgitation — Most studies of ischemic MR have focused on chronic postinfarction MR rather than acute MR in the setting of acute myocardial infarction (MI, ie, with papillary muscle rupture [10]) or reversible MR caused by acute ischemia. Thus, the term "ischemic MR" is used by primarily to indicate chronic functional postinfarction MR. With ischemic MR, impaired motion of the muscle supporting one of the papillary muscles undermines the mitral apparatus, and MR results from systolic papillary muscle displacement and incomplete coaptation of the mitral leaflets [11]. (See "Acute myocardial infarction: Mechanical complications" and "Role of echocardiography in acute myocardial infarction" and "Chronic secondary mitral regurgitation: General management and prognosis".)

Dilated cardiomyopathy — Dilated cardiomyopathy usually results in MR due to ventricular dilatation with displacement of the papillary muscles and mitral annular dilatation; severe regurgitation is unusual in this setting. TTE is usually adequate to evaluate MR in patients with dilated cardiomyopathy.

Hypertrophic cardiomyopathy — In hypertrophic cardiomyopathy, the mechanism of MR may be better elucidated by TEE. The MR usually results from systolic anterior motion of the mitral valve. TEE may better characterize the degree of MR and exclude chordal rupture, a rare complication that causes acute severe MR [12,13]. (See "Hypertrophic cardiomyopathy: Morphologic variants and the pathophysiology of left ventricular outflow tract obstruction".)

Severity of mitral regurgitation — While there are many parameters to assess the severity of MR [14], a systematic approach is recommended by the American Society of Echocardiography [15]. Using this approach, mild (1+) and severe (4+) MR are readily differentiated, but distinguishing between moderate (2+) and moderate to severe (3+) MR can be difficult. Evaluation of MR by TTE and TEE are complementary with TTE providing quantitative parameters such as regurgitant volume and regurgitant fraction, and TEE demonstrating superior evaluation of valve morphology and jet characteristics. The limitations of TEE include: the inability to quantitate MR (specifically measurement of regurgitant volume and regurgitant fraction) and the need to provide conscious sedation for the procedure, which alters hemodynamics, sometimes reducing the severity of MR. This issue is especially important in patients with MR secondary to systolic LV dysfunction. An analysis from the Surgical Treatment for Ischemic Heart Failure (STICH) trial in 196 patients with TEE and TTE demonstrated that there is poor agreement between the two methodologies in this population of patients [16].

Color flow Doppler — Due to proximity of the targets and the use of higher frequencies, color flow signals into the left atrium resulting from MR are well-resolved in a TEE examination. Most of the examinations listed below are conducted in one of the long axis views between longitudinal and transverse (0 to 110 degrees).

Features of severe MR by TEE color flow Doppler imaging arise from the high-energy transfer of a large volume of blood into the left atrium. However, even when imaging is optimized (shallow depth, narrow sector angle, low velocity filters on), the appearance of the regurgitant jet on color flow Doppler provides only an estimate of regurgitation severity. To recognize severe MR, the following color jet characteristics should be sought during a TEE examination [17]:

●The proximal isovelocity acceleration of the jet (PISA).

●The jet size, especially the magnitude of the aliased portion.

●The distance the jet penetrates to the posterior wall of the left atrium and whether it encircles the left atrium (the Coanda effect).

●The eccentricity of the jet.

●The width of the vena contracta.

One color Doppler sign usually present in severe MR is a characteristic proximal acceleration of the regurgitant jet appearing as hemispheric shells (appearing as semicircular bands) of differing colors on the ventricular surface of the valve. The PISA can be used to calculate the effective regurgitant orifice area and to derive the regurgitant volume. In vivo and in vitro, this method has proved to be an accurate measure of MR severity [18-20].

The use of PISA to calculate orifice area has been shown to have prognostic value [21]. However, the method requires accurate measurement of both the radius of the PISA and the peak velocity of the regurgitant jet (continuous wave Doppler). These requirements are usually met by TTE but not by TEE.

In severe MR, at a Nyquist setting (aliasing velocity) of around 55m/sec, the diameter of the PISA ring closest to the regurgitant orifice is measured and usually approaches 1 cm. As the color jet crosses the defect in the valve, the width of the jet exceeds 5 mm, and as the jet enters the left atrium, the jet becomes eccentric and hugs the wall of the chamber (Coanda effect) [22,23]. Once entrained on the wall, the wall jet may completely circle the chamber. The jet also tends to penetrate the atrial appendage and one or more of the pulmonary veins.

In severe MR, the color flow pattern in the left atrium demonstrates a mosaic pattern with jet direction dependent on patho-anatomic characteristics. Spontaneous echo contrast is rarely present [24,25]. Any aliased eccentric jet, however small in apparent area, should be considered as representing hemodynamically significant MR until proven otherwise through careful evaluation of the multiple parameters discussed here. Central jets are most often associated with functional MR associated with symmetric leaflet tethering as observed in dilated cardiomyopathy. Although planimetered jet area is more valid in this situation, the severity of MR may be highly variable dependent on hemodynamic conditions.

On a technical note, the failure to carefully limit the area of color flow mapping results in low frame rates, low resolution, and excessive errors. The color flow examination should be directed only at the region of interest and cover as small a portion of the image fan as possible.

The eccentricity and width of the jet have proved more accurate than either the depth or area of the jet. Importantly, severe eccentric jets, such as those due to a flail leaflet, have smaller jet areas than central jets of equal severity [26]. Using TEE, one study found that a vena contracta width of greater than 5.5 mm at its origin had a positive predictive value of 88 percent for grade 3 or 4 MR by angiography [23]. A second study found similar results using TTE imaging; a vena contracta width less 5.5 mm corresponded to a regurgitant fraction of less than 25 percent while a height greater than 8 mm corresponded to a regurgitant fraction of greater than 45 percent [20].

Pulsed wave Doppler — Color flow Doppler characteristics of the mitral regurgitant jet should not be used as the sole indicator of the severity of the regurgitation; spectral flow Doppler provides complementary information.

In the four chamber TEE view, color flow should be used to identify the most well resolved inflow diastolic signal. The pulsed wave Doppler sample volume should be placed between the tips of the leaflets. In severe MR, the velocity at peak inflow is almost always increased to greater than 1.4 m/sec. A velocity of less than 1.0 m/sec virtually excludes severe MR.

In addition to increased inflow velocity, the pattern is strongly E wave dominant, with a small A wave (E/A ratio >2).

Continuous wave Doppler — Several features are seen in severe MR upon study of the continuous wave Doppler systolic patterns of regurgitant mitral flow. If the flow signal can be aligned parallel to the beam, which is especially difficult in TEE, the jet will have the following characteristics:

●Appear highly and uniformly dense throughout its duration except in the setting of late systolic MR such as that that occurs with mitral valve prolapse.

●A well-defined spectral envelope.

●Late systolic truncation or a "Doppler v-wave," resulting from a rapid decrease in the ventriculoatrial gradient as the large volume of regurgitant blood abruptly raises pressure in the left atrium. This sign is most common in acute MR before the left atrium has dilated significantly.

Evaluation of pulmonary veins — TEE evaluation of the pulmonary veins has provided insight into hemodynamics. In MR, this evaluation is a standard part of the examination and usually includes the left upper pulmonary vein, from which flow into the left atrium is usually axial to the beam of interrogation. The right upper pulmonary vein is well visualized in a 90 degree orientation with anterior rotation of the probe. In hemodynamically severe MR, the flow in one or more pulmonary veins usually demonstrates systolic flow reversal, depending upon jet direction [27-29]. Normally, pulmonary venous flow into the left atrium is predominantly systolic.

MR jet flow may enter the pulmonary veins of only one lung and result in unilateral or unilobar pulmonary edema [30]. Patients who have this finding may be misdiagnosed as having lobar pneumonia. (See "Approach to diagnosis and evaluation of acute decompensated heart failure in adults", section on 'Chest radiograph'.)

Two-dimensional echocardiogram — Two-dimensional (2D) TEE of the left ventricle and atrium contains numerous clues to severe MR:

●The LV is spherically dilated and hyperdynamic.

●The left atrium is enlarged at peak systole and has an exaggerated increase in systolic volume.

●The mitral valve itself may have one of the lesions consistent with severe MR, such as a flail leaflet.

Three-dimensional echocardiogram — To date, the finding of severe MR on 3D echocardiography that has been studied is a vena contracta area of 0.4 cm² [31].

Role of intraoperative transesophageal echocardiography — As noted in the ACC/AHA guidelines on valvular disease, intraoperative TEE is indicated to establish the anatomic basis for chronic primary MR (stages C and D) and to guide repair [1]. Intraoperative guidance of mitral valve repair in severe MR is an established indication for TEE and should be performed for all repairs [32,33]. Intraoperative TEE can enhance the success of valve repair and can reliably predict early and late mitral valve dysfunction [34]. In one study of 143 patients undergoing mitral valve repair, 11 patients had grade 3 or greater MR on intraoperative TEE after discontinuation of cardiopulmonary bypass [32]. Of these 11 patients, five underwent mitral valve replacement, five underwent revision of the mitral repair, and one was managed with observation only. A predischarge TTE was performed in 132 patients; when compared to the intraoperative TEE, there was a discrepancy of 1 grade or greater in the estimated severity of MR in only 17 patients (13 percent).

3D TEE has been used for preoperative planning and intraoperatively [35,36]. This technique enables detailed study of valve morphology and quantitative analysis of annular size and leaflet dimensions important to the repair of degenerative mitral valves [37]. As an example, detailed 3D analysis in ischemic MR has demonstrated differences between those with anterior and inferior infarction [38].

Immediately post-cardiopulmonary bypass, the repaired mitral valve is interrogated for residual regurgitation and other less common complications such as iatrogenic MS (due to an undersized annuloplasty ring) or systolic anterior motion of the redundant leaflets leading to LV outflow tract obstruction. Postoperative hemodynamics must be considered in evaluating the adequacy of the repair. Postpump hypotension may lead to an erroneous conclusion about the presence of MR after repair, and blood pressure should be normalized before surgical decisions are made. On the one hand, important regurgitation may be missed because of low afterload in the presence of low systemic vascular resistance. On the other hand, paradoxically significant MR may resolve once hypotension is corrected; in this case, the hypotension is usually due to decreased LV contractility and will respond to inotropic agents.

When postoperative MR with systolic anterior motion of the valve leaflets is detected, the MR may largely resolve and systolic anterior motion may subside in response to administering fluids to increase preload and reducing or discontinuing intravenous inotropic agents and rarely, if ever, requires further surgical intervention [32]. Modifications in surgical technique have reduced the frequency of this complication.

In patients who are not candidates for surgical mitral valve repair, intraoperative TEE is important for detecting the presence of perivalvular leaks after mitral valve replacement.

Role in transcatheter mitral valve repair — TEE has an important role in determining eligibility for and guiding percutaneous mitral valve repair. (See "Transcatheter edge-to-edge mitral repair".)

MITRAL STENOSIS — TTE is the established method for detecting, quantifying, and judging the severity of mitral stenosis (MS) [39] (see "Echocardiographic evaluation of the mitral valve"). However, TEE has a role in the evaluation of MS prior to catheter-based palliative intervention.

Use for percutaneous balloon valvotomy — As noted in American College of Cardiology/American Heart Association guidelines, TEE should be performed in patients considered for percutaneous mitral balloon valvotomy (PMBV) to assess the presence or absence of left atrial thrombus and to further evaluate the severity of mitral regurgitation (MR) [1,40-42]. MR may be underestimated on TTE due to acoustic shadowing [40-42]. PMBV is contraindicated in patients with left atrial thrombus (due to the risk of catheter dislodgement and subsequent embolization) or moderate to severe MR. (See "Percutaneous mitral balloon commissurotomy in adults", section on 'Evaluation of candidates for PMBC'.)

TEE can also establish the likelihood of procedural success by further evaluating the morphology of the mitral valve and its supporting apparatus [43]. Most authors, however, recommend relying on TTE to judge the degree of mobility, calcification, subvalvular disease, and MR [44,45].

3D TEE has been used to measure mitral valve area with excellent agreement between the 3D mitral valve area and the planimetered area on 2D TTE, even in the hands of inexperienced observers [46]. In another study, 3D TEE provided superior evaluation of commissural fusion, an anatomic feature linked to the success of valvuloplasty as well as occurrence of complications [47]. (See "Percutaneous mitral balloon commissurotomy in adults".)

TEE has been used during the procedure to guide trans-septal puncture and balloon placement. It has also been used after the procedure to allow for prompt recognition of major complications (LV or left atrial perforation with tamponade, severe MR, and creation of a large atrial septal defect).

TEE may be particularly beneficial when there is a desire to limit fluoroscopic exposure, as in pregnancy, or when interatrial septal puncture is initially unsuccessful. To date, there are no data to suggest that TEE can reduce the complications associated with percutaneous valvotomy (other than the identification of thrombus in the left atrium/appendage). 3D TEE has now been used to guide balloon valvuloplasty [48]. However, there are no data to suggest that 3D TEE reduces procedural time or is superior to 2D TEE or fluoroscopy. A disadvantage of TEE guidance is that general anesthesia is required.

Spontaneous echo contrast — Spontaneous echo contrast in the left atrium is a dramatic finding on TEE. It is a phenomenon associated with blood stasis within a cardiac chamber or vessel. It appears as smoke-like slowly swirling patterns in the left atrium. Spontaneous echo contrast is believed to be the result of erythrocyte rouleaux formation (ie, red cell aggregation) in the setting of sluggish blood flow and low shear rate conditions [49]. Erythrocyte aggregation is mediated by plasma proteins, especially fibrinogen, which promotes rouleaux formation by moderating the normal electrostatic forces (due to negatively charged membranes) that keep erythrocytes from aggregating [50]. One study of 185 patients with valvular or nonvalvular atrial fibrillation (AF) found that spontaneous echo contrast was related to the presence of anticardiolipin antibody, a high erythrocyte sedimentation rate, and increased fibrinogen levels [51]. Spontaneous contrast should be considered as an important marker for embolic risk. The incidence of emboli in patients with this finding may be as high as 45 percent [52-54].

Spontaneous echo contrast is common in patients with MS. In one TEE study of 47 patients in sinus rhythm, 47 percent had this finding, which was associated with a smaller mitral valve area and a higher gradient [55]. In another series of 128 patients with mitral valve disease or a mitral valve prosthesis, one-third demonstrated spontaneous echo contrast; those with this abnormality had larger left atria, more frequent AF, and, most importantly, a higher incidence of left atrial thrombi (60 versus 28 percent) [56]. Interestingly, pure MR was never associated with spontaneous contrast in this report; however, others have noted spontaneous echo contrast in occasional patients with moderate or moderately severe MR [52,57,58].

Left atrial appendage — Determination of left atrial appendage function has a complementary role to spontaneous echo contrast in assessing embolic risk [59]. A study that included 29 patients with nonrheumatic AF found that the 10 patients with left atrial appendage contractile velocities below 0.25 m/second were at greater risk for embolic events. Patients with the low flow profile also had high rates of spontaneous echo contrast and three had appendage thrombi. (See "Echocardiographic evaluation of the atria and appendages".)

Role of intraoperative transesophageal echocardiography — In most patients with MS who are not candidates for percutaneous balloon valvuloplasty, mitral valve replacement is necessary. Intraoperative TEE should be performed to exclude left atrial and left atrial appendage thrombus to avoid embolization. The tricuspid valve should be interrogated for the presence of tricuspid regurgitation, although the decision for associated tricuspid valve repair should be based on preoperative echocardiography, as the intraoperative hemodynamics may impact tricuspid regurgitation severity.

Post-cardiopulmonary bypass, it is important to interrogate the prosthetic valve for regurgitation. Color flow Doppler with 3D TEE can be useful in detecting perivalvular regurgitation after mitral valve replacement [60]. When there is associated tricuspid valve repair, evaluation for residual tricuspid regurgitation is important. If the left atrial appendage is ligated to reduce the risk of future embolic events, residual communications should be sought.

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

●While transthoracic echocardiography (TTE) is the primary diagnostic modality for evaluation of mitral disease, transesophageal echocardiography (TEE) is a helpful adjunct in selected patients. (See 'Mitral regurgitation' above.)

●TEE is indicated in evaluation of patients with chronic primary mitral regurgitation (MR; stages B to D) (table 1) in whom noninvasive imaging provides nondiagnostic information about severity and mechanism of MR and/or status of left ventricular function. (See 'Primary mitral regurgitation' above.)

●Intraoperative TEE is indicated in patients with MR undergoing mitral valve repair for surgical planning and for postoperative evaluation of the efficacy of the repair. (See 'Role of intraoperative transesophageal echocardiography' above.)

●Intraprocedural TEE guidance is integral for the success of percutaneous mitral valve repair.

●TEE is performed prior to percutaneous balloon valvuloplasty to identify atrial appendage thrombus and the severity of MR. The presence of a left atrial appendage thrombus and/or moderate to severe MR are contraindications to balloon valvuloplasty. (See 'Use for percutaneous balloon valvotomy' above.)

●The role of three-dimensional TEE is evolving in the evaluation of mitral valve morphology and assessing both mitral stenosis and MR.