Transesophageal Echocardiography

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1 Transesophageal Echocardiography

Ian G. Burwash, MD , Kwan-Leung Chan, MD

The role of transesophageal echocardiography (TEE) in the diagnosis and management of patients with suspected and overt cardiac disease has evolved with time as a result of refinements in technology and the addition of three-dimensional (3D) TEE.^1,² The portable nature of the technique allows the examination to be performed in a diverse array of clinical settings that include the outpatient ambulatory clinic, intensive care unit, catheterization laboratory, and operating room. Currently, TEE accounts for approximately 5% to 10% of all echocardiography studies performed.

Performance of Transesophageal Echocardiography

Transesophageal echocardiography is a semi-invasive procedure that should be performed only by a properly trained physician who understands the indications and potential complications of the procedure. Both technical and cognitive skills are required for the competent performance and interpretation of TEE studies (Box 1-1), and guidelines on training have been published.² The physician should be assisted by an experienced sonographer whose tasks are to ensure that optimal images are obtained by adjusting the controls of the echocardiographic system and to ensure safety by monitoring the responses of the patient during the procedure. Although family members or friends are usually not allowed in the room when the procedure is being performed, there are situations in which their presence can be helpful. The presence of a parent can have a calming effect when one is dealing with an apprehensive teenager. A friend or relative who speaks the same language can relieve anxiety when dealing with an anxious patient who is not fluent in English.

Box 1-1

Cognitive And Technical Skills Required For The Performance Of Transesophageal Echocardiography

Cognitive Skills

Knowledge of appropriate indications, contraindications, and risks of TEE

Understanding of differential diagnostic considerations in each clinical case

Knowledge of physical principles of echocardiographic image formation and blood flow velocity measurement

Familiarity with the operation of the ultrasonographic instrument, including the function of all controls affecting the quality of the data displayed

Knowledge of normal cardiovascular anatomy, as visualized tomographically

Knowledge of alterations in cardiovascular anatomy resulting from acquired and congenital heart diseases

Knowledge of normal cardiovascular hemodynamics and fluid dynamics

Knowledge of alterations in cardiovascular hemodynamics and blood flow resulting from acquired and congenital heart diseases

Understanding of component techniques for general echocardiography and TEE, including when to use these methods to investigate specific clinical questions

Ability to distinguish adequate from inadequate echocardiographic data and to distinguish an adequate from an inadequate TEE examination

Knowledge of other cardiovascular diagnostic methods for correlation with TEE findings

Ability to communicate examination results to patient, other health care professionals, and medical record

Technical Skills

Proficiency in performing a complete standard echocardiographic examination, using all echocardiographic modalities relevant to the case

Proficiency in safely passing the TEE transducer into the esophagus and stomach and in adjusting probe position to obtain the necessary tomographic images and Doppler data

Proficiency in correctly operating the ultrasonographic instrument, including all controls affecting the quality of the data displayed

Proficiency in recognizing abnormalities of cardiac structure and function as detected from the transesophageal and transgastric windows, in distinguishing normal from abnormal findings, and in recognizing artifacts

Proficiency in performing qualitative and quantitative analysis of the echocardiographic data

From Pearlman AS, Gardin JM, Martin RP, et al: Guidelines for physician training in transesophageal echocardiography: recommendations of the American Society of Echocardiography Committee for Physician Training in Echocardiography. J Am Soc Echocardiogr 5:187-194, 1992.

Transesophageal echocardiography should be performed in a spacious room that can comfortably accommodate a stretcher. The room should be equipped with an oxygen outlet and suction facilities. A pulse oximeter should be available, to be used mainly in cyanotic patients and patients with severe lung disease. The TEE probe should be carefully examined before each use. In addition to visual inspection, it is important to palpate the probe, particularly the flexion portion, to ensure that there is no unusual wear and tear of the probe.³ Stretching of the steering cables may result in increased flexibility and mobility of the probe tip with buckling of the probe tip within the esophagus.⁴ This phenomenon is associated with a poor TEE image and resistance to probe withdrawal. The probe should be advanced into the stomach and straightened by retroflexion of the extreme antiflexed probe tip. We have also detected perforation of the TEE probe sheath by a ruptured steering cable and recommend inspection of the casing for any protruding wires before probe insertion.³ The flexion controls need to be tested on a regular basis. Anterior flexion should exceed 90°, and right and left flexion should approach 90°.

Preparation Of Patient

Patients should be contacted at least 12 hours before the procedure and instructed to fast for at least 4 hours before the procedure. They are informed that they should be accompanied, because they will not be able to drive or return to work for several hours owing to the lingering effect of sedation. On the day of the study, the procedure is explained in detail, and informed consent is obtained. Patients are told to expect mild abdominal discomfort and gagging following the insertion of the probe and are reassured that these responses are transient. A 20-gauge intravenous cannula is then inserted for administration of medications and contrast agents, if necessary. Lidocaine hydrochloride spray is routinely used for topical anesthesia, which should cover the posterior pharynx and tongue. We usually use diazepam 2 to 10 mg intravenously for sedation.⁵ Midazolam at 0.05 mg/kg, with a total dose between 1 and 5 mg, can also be used.

Sedation is used in about 85% of our patients and should be more sparingly used in elderly patients, because they tend to be more stoic and the effect of sedation tends to be more prolonged. On the other hand, sedation is essential in young, anxious patients and when the study is expected to be protracted. We aim for light sedation so that at the end of the procedure the patients are awake and can leave with an escort. Heavy sedation is needed in situations in which blunting the hemodynamic responses to the procedure is desirable, as with a patient undergoing TEE for suspected aortic dissection.⁶

It has not been our practice to use anticholinergic agents such as glycopyrrolate to decrease salivation. In rare circumstances in which there is excessive salivation, it is usually adequate to simply instruct the patient to let the saliva dribble onto a towel placed under the chin, or remove the saliva by intermittent suction. Bacteremia is not a significant risk in TEE, and we do not use antibiotic prophylaxis to prevent endocarditis even in patients with prosthetic valves.^7,⁸

Esophageal Intubation

We perform the TEE study with the patient in the left decubitus position. The physician, sonographer, and echocardiographic system are all positioned on the left-hand side of the patient.⁵ Artificial teeth or dentures are routinely removed. The flexion controls should be unlocked to allow for maximum flexibility of the probe when it is being inserted. The patient’s head should be in a flexed position. The tip of the probe is kept relatively straight and gently advanced to the back of the throat. It should be maintained in a central position, because deviation to either side increases the likelihood that it may become lodged in the piriform fossa. (See Fig. 2-2) The operator can facilitate this process by inserting one or two fingers into the patient’s oropharynx to direct the path of the probe. Gentle pressure is exerted, and the patient is instructed to swallow. The swallowing mechanism helps guide the probe into the esophagus. In older patients, cervical spondylosis with prominent protrusion into the posterior pharynx can create difficulty with passage of the probe.⁵ Manually depressing the back of the tongue provides more room, allowing the TEE probe to assume a less acute angle and facilitating intubation of the esophagus. If significant resistance is encountered when the probe is advanced, it is prudent to withdraw the probe and then initiate a new attempt. In experienced hands, the rate of failure of esophageal intubation should be less than 2%.^5,⁹

A bite guard should always be used, except in edentulous patients. Our practice is to put it between the patient’s teeth before the TEE probe is passed into the oropharynx and esophagus because patients with a sensitive pharynx may close their mouths involuntarily during esophageal intubation. The patient is instructed to keep the guard between the teeth throughout the procedure, and regular checks are made to ensure that it is in the proper position to prevent damage to the probe or injury to the patient.

Even when the probe is inserted without difficulties, it is not uncommon for the patient to develop nausea with or without mild retrosternal or abdominal discomfort. We find it useful to pause for 10 to 15 seconds to allow these symptoms to subside before proceeding with echocardiographic imaging. Our practice is to start with images acquired from the esophagus before advancing the probe into the stomach for the gastric views. The gastroesophageal sphincter is usually reached when the probe is advanced 40 cm from the teeth. Gentle pressure is all that is required to advance the probe through the gastroesophageal sphincter. The patient may again experience nausea and mild discomfort, and it may be advisable to pause momentarily for these symptoms to subside. Imaging of the proximal descending thoracic aorta and aortic arch is generally reserved for the end of the study, because the probe needs to be positioned in the upper esophagus, and the patient is generally more aware of the probe at this position and tends to have more discomfort and gagging.

Inadvertent passage of the probe into the trachea can occur, particularly in deeply sedated patients. The development of stridor and incessant cough should alert the operator of this possibility. Furthermore, it would be difficult to advance the probe beyond 30 cm from the teeth, and the image quality is usually poor.⁵

In patients on mechanical ventilation, esophageal intubation is more difficult. We usually introduce the probe with the patient lying supine, because the airway is protected and aspiration is unlikely. The probe is positioned behind the endotracheal tube and gently advanced. It is helpful to have the patient’s mandible pulled forward when the probe is being advanced. If there is undue resistance at about 25 to 30 cm from the teeth, slight deflation of the endotracheal tube cuff can be considered to ease passage of the probe. We do not usually remove the gastric tube, which can be used as a guide to help in proper positioning and passage of the TEE probe. In a minority of intubated patients, successful esophageal intubation may be achieved only with direct laryngoscopy.

Image Format

There is no general agreement on how the imaging planes should be displayed. Our preference is to orient the images such that the right-sided structures are on the left side of the screen and the left-sided on the right. The apex of the imaging plane with the electronic artifact is at the top of the screen. Thus, in longitudinal views, superior structures are to the right of the screen and the inferior to the left.¹⁰

Standard Imaging Planes

The TEE probe should be capable of multiplane imaging and preferably also real-time 3D imaging. The imaging plane is steered electronically from 0° to 180° by means of a pressure-sensitive switch, providing views that are unobtainable using monoplane and biplane probes. The following discussion focuses only on standard imaging views routinely performed at the University of Ottawa Heart Institute using multiplane TEE (Table 1-1). These views are considered “standard” because they have important clinical relevance and can be obtained in most patients with specific imaging planes. Further advances in image quality and image analysis of 3D TEE will likely facilitate the rapid acquisition of these imaging planes.

TABLE 1-1 Standard Imaging Planes with Multiplane Transesophageal Echocardiography*

Four basic maneuvers are used to obtain specific tomographic views with TEE.¹¹ The first relates to the positioning of the probe by advancement or withdrawal of the probe. Although this is a simple maneuver, it is the most crucial, and the imaging views can be conveniently categorized according to the location of the TEE probe within the esophagus or stomach into four groups: basal, four-chamber, transgastric, and aortic views (Fig. 1-1). The second maneuver involves rotation of the probe from side to side. This is particularly useful when using longitudinal imaging planes, which provide a better demonstration of the continuity between vertically aligned structures such as the superior vena cava and the arch vessels (Fig. 1-2).^10,¹¹ Steering the imaging plane using the pressure-sensitive switch is the third maneuver to obtain different tomographic views (Fig. 1-3). The accompanying images in Figures 1-1, 1-2, and 1-3 represent the typical images obtained with one of the basic maneuvers and provide the starting points for further adjustment of the imaging plane to obtain optimal long- or short-axis views of specific structures. This may be achieved using the fourth maneuver, which involves manipulation of the anterior-posterior and right-left flexion control knobs. The availability of a steerable imaging plane has drastically reduced the need to use the flexion knobs, but there are situations in which these knobs play a crucial role in obtaining proper tomographic views.¹¹ These maneuvers provide an almost infinite number of imaging planes. Table 1-1 summarizes the standard imaging planes and the cardiac structures evaluated in these four groups of views.

Figure 1-1 Diagram showing the transesophageal echocardiography transducer locations for the four standard imaging views: basal (A), four-chamber (B), transgastric (C), and aortic (D). Ao, Aorta; DA, descending aorta; PA, pulmonary artery.

Figure 1-2 Diagram showing the transesophageal echocardiography longitudinal imaging planes obtained by rotation of probe: atrial septum (A), RV outflow tract (B), and two-chamber view (C).

Figure 1-3 Diagram showing the transesophageal echocardiography rotational imaging planes (0°-180°): aortic valve (A, 40°), superior vena cava (B, 100°), and LV outflow tract (C, 140°). RAA, Right atrial appendage.

Basal Views

The basal group of views is obtained with the TEE probe located in the midesophagus. The base of the heart, particularly the aortic valve, is well seen. The relationship of the two great arteries can be very well defined and followed cephalad to at least the level of the pulmonary bifurcation. Beyond this level, the interposing trachea makes imaging impossible. Three tomographic planes are found to be particularly useful and are routinely performed at our laboratory.

Aortic Valve

A short-axis view of the aortic valve can be obtained with the probe at about 30 to 35 cm from the teeth. The left coronary cusp often appears to have nodular thickening if the aortic valve is cut obliquely, which is often the case at 0°.¹⁰ Steering the imaging plane to 30° to 60° should eliminate this artifact by providing an optimal short-axis view of the aortic valve (see Fig. 1-3, A).¹¹ A slight pull-back of the transducer should allow visualization of both the left and right coronary arteries (Fig. 1-4). The left coronary artery can be followed to its bifurcation into the left anterior descending and circumflex arteries. The right coronary artery is more difficult to display, and only the proximal 2 to 3 cm is usually seen. Other structures well seen in this view are the left atrial appendage and left pulmonary veins. The partition between these structures can be quite bulbous and should not be confused with an abnormal intracardiac mass (Fig. 1-5).¹² Rotating the probe to the right should reveal the right pulmonary veins.

Figure 1-4 The right (short arrow) and left (long arrow) coronary arteries can be imaged. The latter can frequently be followed to the bifurcation such that the proximal portions of the left anterior descending and the circumflex arteries can also be imaged. Ao, Aorta.

Figure 1-5 The bulbous partition (arrow) between the left upper pulmonary vein and the left atrial appendage (LAA) is demonstrated. LSPV, Left superior pulmonary vein.

We like the horizontal plane in imaging the four pulmonary veins. The left and right pulmonary veins are imaged separately. When one pulmonary vein is identified, a slight translational movement of the probe should bring out the other, because the orifices of the superior and inferior pulmonary veins are in close proximity. The inferior pulmonary veins run horizontal to the imaging plane, whereas the superior veins are more anterior and at an obtuse angle, making them more suitable for Doppler assessment. It is feasible to image the superior and inferior pulmonary veins, left or right, in the same view using the vertical plane and imaging can be facilitated with the use of color flow imaging (Figs. 1-6 and 1-7). The right and left atrial appendages wrap around the great arteries anteriorly. The left atrial appendage is more prominent and can consist of multiple lobes (Fig. 1-8).¹³

Figure 1-6 The two right pulmonary veins are demonstrated using the longitudinal plane, and their identification can be facilitated by color flow imaging. The superior vein provides better Doppler spectral signal due to its parallel alignment with the ultrasound. RIPV, Right inferior pulmonary vein; RSPV, right superior pulmonary vein; SVC, superior vena cava.

Figure 1-7 The two left pulmonary veins are demonstrated using the longitudinal imaging plane. As with the right-sided counterparts, the superior vein is preferred for Doppler interrogation. LIPV, Left inferior pulmonary vein; LSPV, left superior pulmonary vein.

Figure 1-8 The left atrial appendage (LAA) can have multiple lobes that can be readily assessed using X-plane imaging with the 3D transesophageal probe. Two lobes (arrows) are demonstrated at −15° (and not at 70°).

A comprehensive interrogation using multiple imaging planes should be performed to exclude left atrial appendage thrombus in the appropriate clinical setting. The right atrial appendage is smaller and triangular in shape (see Fig. 1-3, B). The endocardial surfaces of both appendages are corrugated and should not be confused with small thrombi.¹² A long-axis view of the aorta can be achieved with the imaging plane at about 120° (Fig. 1-9). A more rightward imaging plane, such as 150°, may be needed if the ascending aorta is dilated and tortuous. This view allows the visualization of a longer length of the ascending aorta and thus significantly reduces the blind spot caused by the interposing trachea.

Figure 1-9 Slight withdrawal of the probe relative to the probe position used to acquire the image shown in Figure 1-3, C, shows the right pulmonary artery (RPA) in short axis and more of the ascending aorta.

Atrial Septum

We prefer to image the atrial septum using the longitudinal plane at 90° to 120°. The fossa ovalis, which is the thinnest part of the atrial septum, and the continuity of the superior vena cava with the RA are very well demonstrated in this view (see Fig. 1-3, B). This view is particularly valuable in demonstrating the sinus venosus atrial septal defect, which is usually located just inferior to the entrance of the superior vena cava.^14,¹⁵ The foramen ovale, if present, is located at the superior aspect of the fossa ovalis and is readily seen in this view. It is important to advance the probe to the level of the inferior vena cava so as not to neglect the inferior aspect of the atrial septum.¹⁶ Careful sweep of the atrial septum with left-right rotation is needed to visualize the entire atrial septum. Continuous rotation from right to left will sequentially demonstrate the left ventricular (LV) outflow tract and the right ventricular (RV) outflow tract (see Fig. 1-2, B).

Pulmonary Bifurcation

The pulmonary bifurcation view is achieved by withdrawal of the probe with the imaging plane at 0°. The pulmonic valve and main pulmonary artery are best seen slightly superior to the aortic valve (Fig. 1-10). The pulmonic valve is thinner than the aortic valve and is usually difficult to image in true cross section. Further slight withdrawal allows imaging of the pulmonary bifurcation. The entire length of the right pulmonary artery, but only the very proximal portion of the left pulmonary artery, can be seen. The right pulmonary artery can usually be followed to its first bifurcation by rotation of the probe rightward, but this maneuver is better performed with the longitudinal plane at 90°. Gradual rotation from left to right provides good visualization in cross section of the entire right pulmonary artery and its first bifurcation. This is an important view in the detection of proximal pulmonary emboli.^17,¹⁸

Figure 1-10 The bifurcation of the main pulmonary artery (MPA) into the right (RPA) and left (LPA) pulmonary arteries is shown using the transverse plane. Ao, Aorta.

Four-Chamber Views

Four-chamber views are obtained with the transducer within the middle to lower esophagus (see Fig. 1-1, B). It is difficult to image the left ventricle in its true long axis. Excessive anterior flexion should be avoided to prevent foreshortening of the ventricles. Indeed, to optimize visualization of the left ventricle, it is advisable to withdraw the probe slightly and at the same time attempt gentle retroflexion while maintaining adequate contact between the imaging surface and the esophagus. In the setting of a dilated and unfolded aorta, rotating the imaging plane to about 20° to 30° may be necessary to obtain the four-chamber view without the aorta obscuring the tricuspid valve and part of the RV.

Left Ventricle

The inferior septum and anterolateral wall are usually seen in the four-chamber view (see Fig. 1-1, B). The LV apex is difficult to visualize, particularly in patients with a dilated LV. In addition to retroflexion, rightward flexion can often be helpful to minimize foreshortening of the LV. Far-field imaging can be improved by decreasing the transmission frequency or by using harmonic imaging. A continuous sweep from 0° to 180° should be performed to examine the different left ventricular segments so as to have a comprehensive assessment of left ventricular global and regional function (see Fig. 1-2, C).

Mitral Valve

The mitral valve is well seen using the four-chamber view, but the depth of the imaging plane should be reduced to enhance the resolution of the image (see Figs. 1-1, B, and 1-2, C). To identify the individual scallops of the anterior and posterior mitral leaflets, a careful sweep from 0° to 180° should be made. The technique of visualizing specific scallops of the mitral leaflets has been published,¹⁹ but patient-to-patient variation should be kept in mind. The presence of a good long-axis view of the aortic valve and proximal ascending aorta, usually at 120°, is a good indication that the middle scallops of both the anterior and the posterior mitral leaflets are imaged and provides the internal reference for the analysis of the other imaging planes. Both papillary muscles can be imaged, but usually not in the same plane. The subvalvular chords are seldom completely imaged because they are frequently obscured by the mitral leaflets. The morphologic information obtained from this view should be corroborated by the short-axis view of the mitral valve obtained from the transgastric view, which also allows a better assessment of the subvalvular structures, including the papillary muscles and chords. Four-chamber views are ideal for the assessment of mitral regurgitation in relation to the number of regurgitant jets, the direction of the jets, and the severity of regurgitation.^20,²¹

Left Ventricular Outflow Tract

We like to image the left ventricular outflow tract at 120° to 160°, because the outflow tract has a horizontal alignment in this plane that may allow optimal imaging even in the setting of a prosthetic aortic valve (see Fig. 1-3, C). The opening and closing of the aortic valve as well as the presence or absence of aortic regurgitation can be well visualized. The proximal ascending aorta is present in this view. A slight withdrawal of the probe will allow more of the ascending aorta to be visualized (see Fig. 1-9). A slight rotation to the left will show the RV outflow tract with the thin pulmonic valve. The motion of the pulmonic valve and the presence or absence of pulmonic regurgitation can be adequately assessed using this view.

Transgastric Views

There is slight resistance during the passage of the TEE probe through the gastroesophageal junction, and the appearance of the liver is a clear indication that the probe is in the stomach. Anterior flexion, often with leftward rotation and flexion, is required to achieve good contact between the imaging surface and the gastric wall. Extreme anterior flexion with further advancement of the probe can sometimes produce images similar to the five-chamber view obtained from the subxiphoid surface approach.

Left Ventricle

Multiple cross sections of the LV can usually be obtained using the transgastric approach (see Fig. 1-1, C, and Fig. 1-11). These are the views commonly used in the intraoperative assessment of LV function.¹⁹ Optimization of the short-axis views of the left ventricle can be achieved with leftward rotation accompanied by leftward flexion. To visualize the LV apex, gentle advancement of the probe is required together with slight retroflexion. In our experience, the short-axis view of the LV apex can be obtained in about 60% of cases. Another way to visualize the LV apex is to use the longitudinal plane at about 90° (see Fig. 1-11). Careful lateral rotation can be used to obtain comprehensive regional assessment of the LV. Leftward rotation of this imaging plane can yield a good alignment with the LV outflow tract and aortic valve to allow accurate measurement of the transaortic pressure gradients in the setting of aortic stenosis (Fig. 1-12).²² The RV can be seen with rightward rotation of the probe. Both short- and long-axis views of the tricuspid valve are achievable, although the tricuspid valve and its papillary muscles are better assessed with the long-axis plane.

Figure 1-11 The short- and long-axis views of the LV are demonstrated using X-plane imaging from the transgastric window.

Figure 1-12 Transgastric window is used to assess the severity of aortic stenosis using CW Doppler echocardiography.

Mitral Valve

The mitral valve can be best assessed using the horizontal imaging plane with the transducer brought up to near the gastroesophageal junction (Fig. 1-13). Anterior flexion and leftward flexion are usually required to optimize this view. Adjusting the imaging plane to about 20° will help to bring out the lateral commissure. This view provides unambiguous assessment of the individual scallops of both the anterior and posterior mitral leaflets and thus should be attempted in all patients with myxomatous mitral valve degeneration. In our experience, this view is achievable in about 70% of patients. Both papillary muscles and chords can be demonstrated, and the continuity between these structures and the mitral leaflets is best seen in the long-axis plane.

Figure 1-13 Transgastric view of the mitral valve (arrowheads) in the short axis showing the circular orifice of the mitral valve in early diastole.

Coronary Sinus

The coronary sinus comes into view when the probe is withdrawn to near the gastroesophageal junction and the flexion knobs are in relatively neutral positions (Fig. 1-14). This view can also be achieved by retroflexion with the probe in the lower esophagus. The coronary sinus is seen as a vascular structure located posterior to the LV at the atrioventricular groove draining into the RA. The tricuspid valve can be visualized to the right and anterior. A dilated coronary sinus should raise the possibility of the presence of a persistent left superior vena cava, which is the most common cause. Leftward rotation while following the coronary sinus may sometimes demonstrate this anomalous vein.²³ In the esophageal views, the left superior vena cava is usually sandwiched between the left atrial (LA) appendage and left superior pulmonary vein.²⁴

Figure 1-14 The coronary sinus (CS) is demonstrated with the probe at the gastroesophageal junction.

Aortic Views

The thoracic aorta is well assessed by TEE because of its close proximity to the esophagus.

Descending Thoracic Aorta

The best way to assess the descending thoracic aorta is to use the horizontal imaging plane with the transducer rotated leftward and posterior, followed by slow withdrawal from the level of the diaphragm to the aortic arch (see Fig. 1-1, D).¹² Because of the relationship between the esophagus and aorta, slight rotational adjustment is required to visualize the entire circumference of the aortic wall as the probe is slowly withdrawn.²⁴ If the aorta is dilated or tortuous, proper short-axis views of the descending aorta will require adjustment of the imaging plane by 0° to 90°.

Aortic Arch

The longitudinal imaging plane at 90° is preferred in imaging the aortic arch because it allows visualization of the entire circumference of the aorta (Fig. 1-15).²⁴ Anterior rotation of the longitudinal plane should visualize the entire aortic arch, but the proximal aortic arch may not be visualized when the aortic arch is unfolded. The transducer will need to be withdrawn slightly to image the arch vessels, which course superiorly. In one third of patients, all three arch vessels can be imaged, but in the other two thirds of patients, only the two distal arch vessels can be imaged. It is rare not to be able to image at least one arch vessel. As a rule, the brachiocephalic artery, which is anterior and more rightward, is the most difficult to image because of the interposing trachea. The transverse plane in a more superior location may sometimes show the three arch vessels in their short axis. Advancing the probe by 1 to 2 cm so that the imaging plane is just inferior to the aortic arch can frequently image the proximal left pulmonary artery. It is sometimes possible to follow it to the first bifurcation. This view should be sought in patients suspected of having pulmonary embolism.

Figure 1-15 The aortic arch is imaged using the longitudinal plane, showing the origin of the left subclavian artery (LSA). PA, Pulmonary artery.

Three-Dimensional Imaging

Advances in transducer technology have enabled the incorporation of real-time 3D-imaging capacity into the commercially available TEE probe, such that 3D imaging can be readily performed during a conventional two-dimensional (2D) TEE study providing unique anatomic perspectives in a number of clinical situations.²⁵^–³² (See Chapter 4.) The current clinical indications of 3D TEE are summarized in Table 1-2, and the indications are likely to increase with time. In our opinion, 3D TEE imaging should be routinely performed in patients with mitral valve disease and congenital heart disease (Fig. 1-16).

TABLE 1-2 Common Indications for Using Real-time Three-Dimensional Transesophageal Echocardiography

Cardiac Structure	Information from 3D TEE	Clinical Situations
Mitral valve	En-face view of mitral valve	Assessment of the location of prolapsing or flail mitral leaflet scallops for potential mitral valve repair; intraoperative assessment of mitral valve clip repair.
Prosthetic valve	Number, size, and location of perivalvular regurgitant jets	Preoperative and intraoperative assessment for device closure of perivalvular regurgitation
Atrial septum	Number, size, and location of atrial septal defect	Preoperative and intraoperative assessment for device closure of atrial septal defect
Intracardiac baffle or conduit	Better anatomic perspective of intracardiac abnormalities	Assessment of naïve and postoperative complex congenital heart disease

Figure 1-16 The individual scallops of the anterior (A1, lateral scallop; A2, middle scallop; A3, medial scallop) and posterior mitral leaflets (P1, lateral scallop; P2, middle scallop; P3, medial scallop) in diastole (left panel) and systole (right panel) are shown using the 3D zoom mode. AML, Anterior mitral leaflet.

The currently available 3D TEE probe can perform 3D imaging in several modes: 3D full volume, 3D zoom, 3D live, 3D color-flow imaging, and X-plane imaging. We find 3D zoom and X-plane imaging to be the most useful. To acquire 3D full volume, the full pyramidal volume is obtained by stitching together four subvolumes gated to the R-wave of the electrocardiogram. To minimize the stitch artifact between the subvolumes, it is best to acquire the images during a breath hold (Fig. 1-17). In this mode, frame rates are relatively low. Although analysis of the volumetric data set can be performed online, it is frequently performed offline so as not to prolong the study. In the full-volume mode, the semiautomatic multiple parallel slice display can be a quick and useful format in the assessment of LV topography, such as in patients with regional wall motion abnormalities or ventricular aneurysms.

Figure 1-17 Transesophageal 3D view of the bioprosthetic mitral valve in the full volume mode shows the stitch artifact (arrows) between the subvolumes.

In the real-time live 3D mode, the 3D data set is displayed in real time. It is important to minimize the sector angle so as to increase the frame rate, which is considerably reduced compared to 2D imaging. We find the 3D zoom mode to be the most versatile. In the 3D zoom mode, the area of interest is identified and encompassed by the zoom box, generally in two orthogonal planes. The height and width of the zoom box are adjusted to include the entire area of interest and at the same time streamlined as much as possible in order to enhance the frame rate. Indeed, the 3D zoom mode is our preferred display format when using the 3D live mode. The availability of the X-plane is a very welcome addition to TEE imaging. It allows the simultaneous display of an additional plane during standard 2D imaging. The orientation of the additional plane is usually orthogonal but can be easily adjusted to any specific orientation. The availability of the X-plane provides a quick and comprehensive assessment of complex structures. One example is the LA appendage, which frequently has multiple lobes (see Fig. 1-8). The use of the X-plane allows rapid assessment of the multiple lobes. Similarly, when multiple mitral regurgitant jets are present, X-plane imaging can readily identify the number and orientations of the regurgitant jets.

Real-time 3D color flow imaging can also be performed to provide a 3D assessment of the color flow jet, but the volume of interest is small, and the frame rate is quite limited in this mode.^33,³⁴ In vitro and early clinical studies have suggested that 3D color flow imaging gives a more accurate assessment of the shape and size of the vena contracta and flow convergence, both of which are important measures of mitral regurgitation severity. Its clinical usefulness, however, remains unclear.

In order to obtain a high-quality 3D image, the 2D image needs to be optimized in terms of gain and compression settings. A slightly higher gain setting generally provides better 3D images. In both the 3D zoom and 3D live modes, the zoom box should be streamlined to focus on the area of interest to maximize the frame rate. Because the best 3D imaging is obtained with the structure close to the transducer and orthogonal to the ultrasound beam, the TEE transducer should be manipulated to achieve these two objectives. For instance, the transgastric window is superior to the transesophageal window in 3D imaging of the LV papillary muscles. The mitral valve is well suited for 3D TEE imaging precisely for these reasons (see Fig. 1-16). On the other hand, it is much more difficult to obtain a good 3D image of the aortic valve because the valve plane is frequently parallel to the ultrasound beam.

Doppler Examination

Transesophageal echocardiography can be used to assess the flow patterns across the four cardiac valves, but it does not provide additional information to transthoracic echocardiography (TTE). Furthermore, good ultrasound beam alignment with the transvalvular flow may not be feasible because of the anatomic confines of the esophagus. However, accurate Doppler assessment of aortic stenosis can often be obtained from the transgastric window (see Fig. 1-12).²² On the other hand, intracardiac flows such as pulmonary vein flow and LA appendage flow are better and more consistently obtained by TEE and provide important insight into intracardiac hemodynamics.

Left Atrial Appendage Flow

The LA appendage can be imaged from the midesophagus aortic valve short-axis view (30° to 60°) or the midesophagus two-chamber view (80° to 100°). LA appendage flow should be recorded by positioning the color flow sector over the LA appendage and placing the pulsed-Doppler sample volume at the site of maximal flow velocity. This usually occurs in the proximal or middle third of the LA appendage. Velocity recordings from the distal third of the LA appendage frequently have wall motion artifacts and are usually unsatisfactory. Wall filters should be set low, because low-velocity flow may be present.

The pattern of LA appendage flow is dependent on cardiac rhythm.^35,³⁶ In atrial fibrillation, a regular atrial contraction wave is absent. (See Chapter 42.) In atrial flutter, the velocity waves are more regular and tend to be of greater velocity because of the slower atrial rate. The normal LA appendage velocities are as follows: contraction, 60 ± 14 cm/s; filling, 52 ± 13 cm/s; and early diastolic filling, 20 ± 11 cm/s.^35,³⁷

The potential clinical utility of measuring LA appendage velocities relates to their association with LA spontaneous echo contrast and LA thrombus.^35,^36,^38,³⁹ Patients with atrial fibrillation and a LA appendage emptying velocity less than 20 cm/s are more likely to have LA thrombus and have a 2.6-fold greater risk of ischemic stroke compared to patients with a velocity greater than 20 cm/s.^38,³⁹ Lower LA appendage velocities have also been observed in stroke patients in normal sinus rhythm.⁴⁰ LA appendage velocities may predict successful cardioversion of atrial fibrillation⁴¹ and the maintenance of sinus rhythm at 1 year.^35,^36,⁴²

Pulmonary Vein Flow

Pulmonary venous flow patterns provide unique and ancillary information for evaluating LV diastolic function, measuring LV filling pressure, assessing mitral regurgitation severity, differentiating constrictive pericarditis from restrictive cardiomyopathies, and identifying pulmonary vein stenosis after radiofrequency ablation of atrial fibrillation.⁴³^–⁴⁵ TTE can obtain pulmonary vein flow in up to 90% of patients; however, TEE allows a more consistent and reliable acquisition of high-quality laminar Doppler signals.^43,⁴⁶

The pulmonary veins are imaged from the midesophagus, and flow is evaluated by placing the pulsed-Doppler sample volume 1.0 to 2.0 cm into the pulmonary veins. The ultrasound beam can be aligned parallel to flow in the left and right superior pulmonary veins; however, this alignment is often not achievable with the inferior pulmonary veins.

Indications for Transesophageal Echocardiography

In general, TTE should be the initial diagnostic investigation, because it is noninvasive and imparts no risk to the patient. However, patient factors (i.e., obesity, emphysema, chest deformities, or subcutaneous emphysema) and the clinical setting (i.e., surgical bandages, mechanical ventilation, or traction) frequently limit ultrasound penetration or proper patient positioning, resulting in a nondiagnostic TTE. TEE can provide excellent cardiac visualization in these situations and should be considered to obtain the necessary diagnostic information.

TEE can also visualize cardiac structures not usually seen by TTE (i.e., the superior vena cava, pulmonary veins, and descending thoracic aorta) and can provide improved anatomic and spatial resolution to both diagnose cardiac pathology and guide patient management. Common clinical indications for TEE are listed in Box 1-2.

Native Valve Disease

The close proximity of the mitral valve to the posteriorly positioned TEE transducer allows excellent visualization of the mitral annulus, leaflets, chordal structures, and papillary muscles. (See Chapters 18 and 19.) Ruptured chordae tendinae can be visualized, and prolapsing or flail scallops can be localized, to predict the potential for successful mitral valve repair.^20,⁴⁷^–⁴⁹ Abnormalities of the papillary muscles, such as a partial or complete rupture, are better visualized by TEE than TTE.⁵⁰ 3D TEE provides superior delineation of the mitral valve anatomy and can more precisely characterize and localize mitral valve pathology compared to 2D TEE.^26,^30,^31,⁵¹

The severity of mitral valve regurgitation can be quantified by TEE using the same methods employed for TTE ⁵²; however, color Doppler regurgitant jet areas tend to be larger on TEE than on TTE.⁵³ 3D color Doppler imaging provides additional information on the mechanism and severity of mitral regurgitation that may not be apparent from 2D TEE.^33,^51,^54,⁵⁵ Pulmonary vein flow can be assessed in nearly all patients and provides a valuable measure of mitral regurgitation severity.^43,⁵⁶ The vena contracta width and regurgitant orifice area, derived by the proximal flow convergence method, can be measured using TEE and can provide prognostic information in patients with asymptomatic mitral regurgitation.⁵⁷^–⁵⁹ The accuracy of these latter measures to quantify mitral regurgitation severity can be improved using 3D TEE.^33,⁵⁵

In mitral stenosis, TEE can assess valve mobility and leaflet thickening, but subvalvular disease and calcification may be underestimated in the esophageal views due to a shadowing effect from the thickened and calcified mitral valve leaflets and annulus.⁶⁰ (See Chapter 21.) Effective orifice area can be derived by the pressure half-time method, proximal flow convergence method, or orifice planimetry.^61,⁶² Accurate orifice planimetry requires a tomographic cut of the distal, most narrowed portion of the mitral orifice. Optimal alignment of the image is frequently not possible using 2D TEE, but may be achievable by 3D TEE.³¹ The suitability of a patient for percutaneous balloon mitral valvuloplasty usually incorporates a TEE evaluation of the LA chamber and appendage to identify thrombus, an assessment of the mitral valve morphology score, and an evaluation of mitral regurgitation severity. Mitral valve morphology on TEE is predictive of the prognosis of patients following percutaneous balloon mitral valvuloplasty; however, TTE is preferred to evaluate valve morphology because of the limitations of TEE in evaluating calcification and subvalvular thickening.^60,⁶³ TEE can be used during transcatheter mitral commissurotomy to guide the transseptal puncture and balloon placement and to identify potential procedural complications (i.e., severe mitral regurgitation, cardiac tamponade, or significant atrial septal defect).⁶⁴ (See Chapter 5.) 3D TEE may provide incremental information during the procedure by confirming the coaxial trajectory of the balloon through the stenotic mitral valve and by better evaluating commissural opening postdilation.^65,⁶⁶

Subaortic membranes frequently require TEE for definitive diagnosis.⁶⁷ Anatomic valve area of a stenotic aortic valve can be measured using multiplane TEE by planimetry of the maximum systolic orifice area in the esophageal short-axis (30° to 60°) view.^22,⁶⁸ Proper transducer position should be confirmed by rotating to the longitudinal plane and verifying that the leaflet tips are being imaged. However, dynamic movements of the aortic valve can cause misalignment of the imaging plane with the narrowest cross-sectional area and result in an inaccurate measurement of the anatomic valve area. 3D TEE can avoid this potential pitfall.⁶⁹ Unfortunately, valve calcification can affect the accuracy of TEE-measured orifice areas using either 2D or 3D techniques.⁷⁰

TEE is rarely necessary to evaluate aortic regurgitation severity. The standard methods used during TTE to quantify aortic regurgitation severity can be used during TEE.^52,⁷¹ Color jet areas on TEE tend to be larger than those obtained during TTE.⁵³ Vena contracta width on TEE correlates well with the regurgitant fraction and regurgitant volume.⁷² Aortic regurgitation severity can also be quantified using the proximal flow convergence method.⁷³ Holo-diastolic flow reversal in the descending aorta can be detected by TEE using pulsed Doppler.⁷⁴

The tricuspid and pulmonic valves can be visualized on TEE; however, TTE generally provides better visualization because of the anterior position of these valves. 3D TEE appears to be of limited value in evaluating these valves. In one study, 3D TEE provided optimal visualization of the tricuspid valve in only 11% of patients.⁷⁵ However, TEE may provide clinically relevant information about the tricuspid and pulmonic valves in patients with poor TTE images.

Prosthetic Valves

TEE is more sensitive for detecting abnormalities of bioprosthetic and mechanical prostheses when compared to TTE.⁷⁶ (See Chapter 25.) Leaflet thickening and calcification, flail leaflets, vegetations, thrombi, filamentous strands, and motion of the occluding device are better appreciated on TEE.⁷⁶^–⁸³ TEE can distinguish pannus from thrombus formation and guide the use of thrombolytic therapy.⁸⁴^–⁸⁷ TEE is especially valuable in assessing a mitral prosthesis, because the transducer’s posterior position provides excellent visualization of vegetations and thrombi that usually locate on the LA aspect of the prosthesis.^76,⁷⁸ However, the ventricular aspect of a mitral prosthesis may not be adequately seen on TEE, and TTE should be performed to complete the assessment.⁸⁸ 3D TEE can provide excellent visualization of a mitral prosthesis ring, leaflets, or strut (mechanical or bioprosthesis).²⁷ The aortic prosthesis ring can also be well seen on 3D TEE; however, visualization of the leaflets can be suboptimal.²⁷

TEE should be performed if significant prosthetic mitral regurgitation is suspected clinically, but not seen on TTE. TEE can distinguish normal variant from pathological prosthetic valve regurgitation and determine whether the regurgitation is paravalvular or transvalvular in origin, potentially modifying the surgical procedure.⁷⁷^–⁸⁰ ⁸⁹ 3D TEE may provide better delineation of the site and extent of paravalvular regurgitation or mitral prosthesis dehiscence compared to 2D TEE.²⁷ The incremental benefit of TEE in assessing prosthetic aortic regurgitation severity is less clear, because the regurgitant jet is usually well seen on TTE, and TEE visualization may be compromised by partial shadowing of the regurgitation jet by either the aortic or mitral prosthesis when imaged in the esophageal views.⁸⁰

All bioprostheses and mechanical prostheses are inherently stenotic, the severity dependent on the prosthesis type and size and the presence of associated pathology such as leaflet calcification, pannus formation, or valve thrombosis. In general, TTE is sufficient to assess the hemodynamic severity of a stenotic aortic or mitral prosthesis, but only TEE has sufficient resolution to distinguish these pathologic conditions.^84,⁸⁵ In patients with an inadequate TTE, TEE can be used to quantify the stenosis severity, as described for native valve stenoses.^22,^62,^68,⁹⁰

Infective Endocarditis

Identification of a vegetation in the clinical setting of suspected endocarditis confirms the diagnosis.⁹¹ Studies comparing TTE and TEE for detecting a vegetation in native valve endocarditis report a sensitivity of 28% to 70% for TTE, substantially lower than the 86% to 100% sensitivity reported for TEE.⁹²^–⁹⁷ (See Chapter 22.) Smaller vegetations are better detected by TEE because of the improved spatial resolution of this technique.⁹³ However, TTE and TEE have a similar specificity that exceeds 90% when strict criteria for diagnosing a vegetation are used.^92,^93,^95,⁹⁷ Pulmonic valve vegetations are better detected by TEE than TTE, despite the anterior position of the pulmonic valve.⁹⁸ In contrast, TEE has not been reported to have a better sensitivity for detecting tricuspid valve vegetations compared to TTE.⁹⁹ However, we would recommend a TEE if there is a clinical suspicion of tricuspid valve endocarditis but the TTE is negative.

Prosthetic valve endocarditis is more difficult to diagnose by either TTE or TEE. The sensitivity of TTE for detecting vegetations ranges from 0% to 43% and increases to 33% to 86% using TEE.^76,^94,^100,¹⁰¹ Clearly, TEE can identify a vegetation in a significant number of patients with a negative TTE and should be performed in patients with suspected prosthetic valve endocarditis if the TTE does not identify a vegetation.¹⁰²

Although TEE provides a greater sensitivity than TTE for detecting vegetations in native and prosthetic-valve endocarditis, TEE has the greatest impact on diagnosis in patients with suspected endocarditis and an intermediate clinical probability of endocarditis.^102,¹⁰³ The absence of a vegetation on TEE in this setting makes the diagnosis of endocarditis unlikely (less than 10%), and alternative diagnoses should be considered.^101,¹⁰⁴ However, a negative TEE does not supplant a clinical and microbiological diagnosis, because false-negative studies have been reported. Patients with a negative TEE study may benefit from a follow-up TEE in 7 to 10 days if there is a high index of suspicion of endocarditis, a prosthetic valve, or persistent bacteremia.¹⁰¹^–¹⁰⁴ TEE is likely not warranted in patients with a low clinical probability of endocarditis, because the diagnostic yield is small.¹⁰³

Complications of infective endocarditis, including abscess formation, leaflet diverticula, leaflet perforation, fistula tracts, mycotic aneurysms, and pseudoaneurysm formation, are significantly better detected by TEE than TTE.^94,¹⁰⁵^–¹⁰⁸ TTE has a low sensitivity (less than 30%) for detecting an abscess,¹⁰⁵ so a patient with a suspected abscess on clinical grounds or persistent bacteremia should undergo TEE despite a negative TTE. TEE can be falsely negative in up to half of patients with an abscess.¹⁰⁸ This often occurs when the abscess cavity is localized on the posterior aspect of a calcified mitral annulus or when a prosthesis is present.¹⁰⁸

The potential utility of TEE in uncomplicated confirmed endocarditis remains to be defined. Large (greater than 10 to 15 mm) or severely mobile vegetations on TEE are associated with systemic embolization, and vegetation size is an independent predictor of survival.^96,^109,¹¹⁰ Furthermore, complications are more likely to occur in patients in whom a vegetation fails to decrease in size with therapy.¹¹¹ Although we routinely perform a TTE in follow-up of patients with uncomplicated confirmed endocarditis to reevaluate vegetation size and valve function, we do not routinely perform a follow-up TEE.

Suspected Cardioembolic Event

Cardiogenic embolism accounts for approximately 15% to 30% of ischemic strokes and should be considered as a potential cause of cerebral ischemia, especially in those patients without significant cerebrovascular disease.¹¹² (See Chapter 41.) Potential cardioembolic sources encompass conditions that have a propensity for thrombus formation, intracardiac or intraaortic masses, and potential passageways for paradoxical emboli. Cardiac abnormalities having a strong association with cardioembolic events include atrial fibrillation, LA or LV thrombi, vegetations, intracardiac tumor, mitral stenosis, mechanical valves, recent myocardial infarction, dilated cardiomyopathy, ischemic LV dysfunction (ejection fraction less than 28%), and intraaortic debris.^113,¹¹⁴ Minor risk sources with weaker associations include atrial septal aneurysms, patent foramen ovale, spontaneous echo contrast, mitral annular calcification, mitral valve prolapse, and calcified aortic stenosis.¹¹³^–¹¹⁵ Although many of these conditions can be diagnosed clinically, echocardiography is frequently necessary to diagnose anatomic abnormalities.¹¹⁶ In general, TEE is superior to TTE at identifying major and minor risk sources.

LA thrombus is usually located in the LA appendage, a region poorly visualized on TTE. TTE has a sensitivity for detecting LA thrombi of only 0% to 53%, whereas TEE has a sensitivity of 93% to 100% and a specificity exceeding 95%.^117,¹¹⁸ Care must be taken not to mistake the pectinate muscles for LA appendage thrombus. LA spontaneous echo contrast is rarely appreciated on TTE but is well seen on TEE. LV thrombi can usually be detected by TTE (sensitivity and specificity approaching or exceeding 90%), and contrast echocardiography can improve the diagnostic accuracy.¹¹⁹ In general, TEE adds no incremental sensitivity unless the TTE is inconclusive, because the apex is located in the far-field position and apical foreshortening is common.^120,¹²¹ TEE may better detect small myxomas or papillary fibroelastomas.^122,¹²³ Similarly, TEE is superior to TTE for detecting an atrial septal aneurysm and patent foramen ovale, although the addition of harmonic imaging to TTE has improved the sensitivity of TTE for detecting a patent foramen ovale.¹²⁴^–¹²⁶ The cardioembolic risk of a patent foramen ovale is related to the defect size, which can be better appreciated by TEE.^127,¹²⁸ Aortic arch atheroma can be detected by TTE; however, TEE is required to adequately assess the extent, degree of lumen protrusion, and morphological features (i.e., mobility, ulceration, calcification) that characterize the potential embolic risk.^38,¹²⁹^–¹³¹

The indication for performing a TEE in a patient with a suspected cardioembolic event is controversial.^113,^132,¹³³ Although TEE has a better sensitivity than TTE for detecting potential cardioembolic sources,^134,¹³⁵ the yield for identifying a major risk source is limited. An analysis of pooled data suggested an overall detection rate for intracardiac masses of only 4% for TTE and 11% for TEE.¹¹³ The yield was greater in patients with cardiac disease (TTE, 13%; TEE, 19%), but small in patients without cardiac disease (TTE, 0.7%; TEE, 1.6%). Of importance, the identification of minor risk source by TEE may not significantly alter patient management. Therefore, TEE should only be performed if the results have a reasonable chance of altering patient management or therapy. In this regard, TEE likely has the greatest potential impact on management when the TTE fails to identify a cardioembolic source in a patient with (1) unexplained cerebral ischemia before 55 years of age, (2) recurrent events or events in multiple cerebrovascular territories, (3) occlusion of a large peripheral or visceral artery, or (4) suspected endocarditis.

Atrial Septal Abnormalities

Atrial septal defects, atrial septal aneurysms, and patent foramen ovale are identified more frequently by TEE than TTE.^14,^124,¹²⁶ Sinus venosus defects and associated anomalous pulmonary venous drainage are easily detected on TEE, but frequently missed on TTE.^14,¹⁵ Therefore, a TEE should be considered in a patient with unexplained right heart dilation despite a negative TTE for intracardiac shunting. (See Chapter 44.) TEE can delineate the morphological details of an atrial septal defect and patent foramen ovale, determine the size of the defect and severity of left-to-right shunting, determine the potential for percutaneous closure, and assist with proper device placement during percutaneous closure.^32,^127,^128,^136,¹³⁷ The en-face view of the atrial septum using 3D TEE and multiplanar reconstruction provides a better appreciation of the defect (i.e., size, presence of multiple defects, septal rim length) and spatial relationships among the defect, occluding device, and surrounding cardiac structures such as the mitral valve and aortic root.^32,^75,^138,¹³⁹

Cardiac Tumors

The sensitivity of TTE and TEE for detecting atrial myxomas has been reported to be 95% and 100%, respectively.¹⁴⁰ (See Chapter 46.) Similar high sensitivities have been reported when detecting nonmyxomatous intracardiac tumors.¹⁴⁰ However, the sensitivities of TTE and TEE are dependent on tumor size and may be as low as 62% and 77%, respectively, for detecting papillary fibroelastomas smaller than 2 mm.¹²³ TEE is superior to TTE for characterizing features of an intracardiac tumor that are important for diagnosis and management, such as the involvement of multiple chambers, site of attachment, presence of multiple tumors, infiltration of adjacent structures, and presence of tumor calcification or cyst formation.^122,¹⁴⁰ TEE can be used to guide percutaneous biopsy of an intracardiac tumor.¹⁴¹ 3D TEE may provide incremental information relevant to deciding the optimal surgical approach.¹⁴²

Pericardial or paracardial tumors are better detected using TEE than TTE.¹⁴⁰ TEE appears especially valuable for detecting tumors located at the base of the heart, adjacent to the great vessels, or adjacent to the right heart.^122,¹⁴⁰ However, the size and extent of paracardial involvement is not usually well delineated using TTE or TEE. Magnetic resonance imaging and computed tomography have a wider field of view and provide a superior evaluation of extracardiac involvement.

Acute Aortic Syndromes

Aortic dissection can be detected by TEE with a high degree of accuracy and is the diagnostic investigation of choice for suspected aortic dissection in many institutions.¹⁴³ (See Chapter 36.) The presence of an intimal flap is diagnostic of aortic dissection and can be distinguished from reverberation artifacts commonly seen in the ascending aorta by using M-mode echocardiography.¹⁴⁴ A small segment of the superior ascending aorta may not be visualized by TEE because of the interposition of the air-filled trachea and bronchus. Multiplane TEE has a sensitivity of 98% to 100% and a specificity of 94% to 95%¹⁴⁵ and can be performed at the bedside of hemodynamically unstable patients. TEE can determine the extent of the dissection and involvement of arch vessels or coronary arteries, differentiate the true and false lumen, identify thrombus within the false lumen, locate the site of the intimal tear, detect signs of rupture, and evaluate for aortic valve involvement and the potential for valve repair.^143,¹⁴⁶ TEE can also guide stent graft implantation for descending thoracic aorta dissections and identify complications following surgical repair.^147,¹⁴⁸

Intramural hematoma and penetrating aortic ulcers have a similar presentation to aortic dissection.^149,¹⁵⁰ TEE has a sensitivity and specificity that exceed 90% for identifying intramural hematoma¹⁴⁵ and can be performed serially to assess for hematoma regression or progression or the development of classic dissection.¹⁵¹ The diagnostic accuracy of TEE for detecting penetrating aortic ulcers is unclear; however, one study reported a sensitivity of 83%.¹⁵² The presence, depth, and diameter of a penetrating ulcer are predictive of disease progression and prognosis.¹⁵³

Traumatic aortic rupture and blunt aortic trauma can be diagnosed by TEE with a sensitivity of 63% to 100% and a specificity of 84% to 100%.^130,¹⁵⁴ TEE can guide the acute management and triage patients for conservative therapy, immediate surgery, or postponed surgical repair.¹⁵⁵ However, TEE cannot consistently visualize the superior ascending aorta and aortic arch branch vessels, a frequent site of traumatic injury.

Atrial Fibrillation

Atrial fibrillation predisposes the LA to contractile dysfunction, chamber dilation, and thrombus formation in approximately 13% of patients with nonrheumatic atrial fibrillation of more than 2 days’ duration.¹⁵⁶ TEE is clearly superior to TTE for detecting LA thrombus and has a sensitivity ranging from 93% to 100% and a specificity greater than 95%.^117,¹¹⁸ In addition, LA appendage velocity less than 55 cm/s on TEE identifies patients at increased risk for thrombus formation.¹⁵⁷ The presence of LA thrombus, spontaneous echo contrast, LA appendage velocity below 20 cm/s, or complex aortic atheroma on TEE identifies patients with atrial fibrillation at higher risk of thromboembolism.^38,¹⁵⁸

A TEE-guided strategy can be used in patients with atrial fibrillation of more than 2 days’ duration to permit “early” cardioversion without a preceding 3 weeks of therapeutic anticoagulation.¹⁵⁹ (See Chapter 42.) This approach provides a therapeutic option for patients at increased risk of a hemorrhagic complication with anticoagulation therapy or who are not tolerating their atrial fibrillation. In the TEE-guided approach, LA thrombus is ruled out by TEE and followed by “early” cardioversion. The TEE-guided strategy had a similar incidence of embolic events, stroke, or transient ischemic attack, but fewer hemorrhagic events, compared to the conventional management strategy.¹⁵⁹ The costs of the two strategies are similar.¹⁶⁰

LA appendage velocity may predict the likelihood of maintaining sinus rhythm post cardioversion ^41,⁴²; however, we do not perform TEE studies in patients with atrial fibrillation solely for this purpose.

Congenital Heart Disease

The potential indications for TEE in patients with congenital heart disease are extensive and encompass the preoperative, interventional, intraoperative, and postoperative management of these patients.¹⁶¹^–¹⁶³ (See Chapters 43–45.) TEE better appreciates abnormalities of the atrial septum and pulmonary veins.^14,^15,^32,^75,^137,¹⁶² The atrioventricular valves and site of chordal insertion are better visualized using TEE if surgical valvuloplasty is being considered for an atrioventricular canal defect.¹⁶⁴ TEE can better appreciate a baffle stenosis or leak, or complication of a Fontan procedure such as obstruction or thrombosis.^165,¹⁶⁶ TEE can characterize outflow tract obstructions^67,¹⁶² or abnormalities of the aorta, such as aortic coarctation or a patent ductus arteriosus.^167,¹⁶⁸ 3D TEE provides incremental information beyond 2D TEE, including a better delineation of the shape of an intracardiac defect, anatomic position, extent of an atrial rim, and potential presence of multiple or fenestrated defects.^32,^139,^169,¹⁷⁰

Coronary Artery Disease

Stress echocardiography with TTE imaging is a widely used technique for evaluating patients with suspected or confirmed coronary artery disease, and the addition of a contrast agent can improve the diagnostic accuracy when endocardial definition is limited.^171,¹⁷² (See Chapters 15 and 16.) In specific clinical situations, TEE can be used to diagnose coronary artery disease by either (1) visualizing coronary stenoses in the proximal vessels, or (2) detecting stress-induced regional wall motion abnormalities.

The left main coronary artery can be visualized in more than 85% of patients using TEE. The proximal left anterior descending artery and left circumflex artery can also be visualized in most patients. The proximal right coronary artery is more difficult to visualize but may be seen in more than 50% of patients. In patients with visualized vessels, TEE has a sensitivity and specificity of greater than 90% for identifying a significant left main coronary artery stenosis.^173,¹⁷⁴ The sensitivity of TEE for detecting significant proximal disease in the left anterior descending artery, left circumflex artery, or right coronary artery is 78% to 100%, 50% to 89%, and 82% to 100%, respectively, but significantly decreases when nonvisualized segments are included in the analysis.^173,¹⁷⁴ However, TEE should not replace coronary angiography in the diagnosis of proximal coronary artery disease, but rather should be potentially used when an angiographic stenosis of the left main or left anterior descending artery is of questionable severity and intravascular ultrasound is unavailable.¹⁷⁵

Stress TEE can be performed using either transesophageal atrial pacing or pharmacologic stimulation with dobutamine or dipyridamole infusion. These techniques are accurate in detecting and risk-stratifying patients with coronary artery disease and can be performed safely in morbidly obese patients.¹⁷⁶^–¹⁷⁹ However, TEE is an invasive procedure with potential risks and should be reserved for patients with poor TTE images.

Additional applications of TEE include the detection of anomalous coronary arteries, coronary artery aneurysms, and coronary artery fistulas.¹⁷³

Pericardial Disease

Cardiac tamponade can be challenging to diagnose early after cardiac surgery. (See Chapter 29.) Localized compression of a cardiac chamber (usually the RA) may not be apparent on TTE because the thrombus is located posteriorly; image quality is poor because of suboptimal patient positioning, surgical bandages, and drainage tubes; and the findings of RA or RV diastolic collapse are frequently absent. TEE circumvents many of these problems and can better detect extracardiac compression.¹⁸⁰ In constrictive pericarditis, TEE with respiratory monitoring can be helpful in patients with a nondiagnostic TTE.^181,¹⁸² Pericardial thickening, pericardial metastases, intrapericardial thrombus, and pericardial cysts are better seen by TEE than TTE.^180,¹⁸³ However, computed tomography and magnetic resonance imaging are better techniques for evaluating pericardial thickness, pericardial calcification, localized pericardial abnormalities, and tissue characterization of a pericardial mass.¹⁸²

Critically Ill Patient In The Intensive Care Unit

TTE image quality in an intensive care unit is frequently inadequate, and in this setting TEE can provide rapid access to diagnostic information that alters patient management.^184,¹⁸⁵ TEE can evaluate myocardial function, valve function, volume status, hemodynamics, and intracardiac shunting, which are critical components for the diagnosis and management of patients with unexplained hypotension, pulmonary edema, or hypoxia.^17,^18,¹⁸⁴^–¹⁸⁷

Monitoring During Surgical And Interventional Procedures

A comprehensive intraoperative TEE can evaluate global and segmental LV function; detect intraoperative myocardial ischemia; monitor hemodynamics including cardiac output, LV filling pressures, and volume status; determine the potential cause of hemodynamic disturbances; and evaluate the adequacy of surgical repairs, replacements or reconstructions before leaving the operating room.¹⁸⁸ (See Chapter 2.) The American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists recently updated their guidelines on the use of perioperative TEE, recommending that intraoperative TEE be used in all open heart and thoracic aorta surgical procedures and be considered during coronary artery bypass graft surgery.¹⁶³ Intraoperative TEE was recommended during noncardiac surgery when the patient has known or suspected cardiovascular pathology that might result in hemodynamic, pulmonary, or neurologic compromise.¹⁶³

TEE is routinely used during percutaneous closure of an atrial septal defect or patent foramen ovale to exclude multiple defects, size the defect, guide positioning of the occluding device, and determine the presence of residual shunting.^137,¹⁷⁰ (See Chapter 5.) 3D TEE can provide additional information relevant to the procedure.^32,¹⁷⁰ Percutaneous closure of a ventricular septal defect is usually performed under 2D or 3D TEE guidance.^32,¹⁷⁰ During percutaneous mitral valvuloplasty, TEE can direct the transseptal puncture, assist with proper balloon placement, evaluate the result, identify any complications, and shorten procedure and fluoroscopy times.¹⁸⁹ For transcatheter aortic valve implantation, TEE can guide proper prosthesis positioning and identify periprocedural complications.¹⁹⁰ During transcatheter closure of a periprosthetic valve leak, TEE can delineate the precise location and extent of any paravalvular jets.¹⁷⁰ 3D TEE can improve spatial appreciation of the regurgitant jets (i.e., number, location, extent), better identify complications, and improve procedural efficiency.^27,³³ TEE can assist with the proper positioning of a LA appendage occluding device, which is essential to avoid complications.³² TEE has also been used to guide catheter ablation of arrhythmias, alcohol septal ablation for hypertrophic cardiomyopathy, and biopsy of the RV or an intracardiac mass.^32,¹⁴¹

Contraindications to Transesophageal Echocardiography

There are few absolute contraindications to performing a TEE (Box 1-3); however, relative contraindications are more frequently encountered in clinical practice. Thus, a critical analysis of the risk-benefit ratio is required based on available information and potential discussion with the attending physician.

An elective TEE should be postponed if the patient has not been fasting for 4 to 6 hours before the procedure because of the risk of vomiting and aspiration. However, an urgent TEE can be performed with minimal risk of vomiting and aspiration if only clear fluids were taken up to 2 hours before the procedure.¹⁹¹ TEE should not be performed in an uncooperative patient who is not heavily sedated or paralyzed to minimize the chance of injury. Patients with a tenuous cardiorespiratory status should be intubated and ventilated to avoid decompensation during the procedure. TEE should not be attempted in a patient with an esophageal obstruction (stricture or mass) because of the potential for esophageal rupture. Upper endoscopy should be considered before performing a TEE if the patient has a history of dysphagia or odynophagia. An esophageal diverticulum is a relative contraindication to TEE because the probe can potentially enter and perforate the diverticulum. Fluoroscopic balloon guidance or a fiberoptic endoscope and overtube can be used to allow a TEE examination in the presence of a Zenker diverticulum.¹⁹² TEE should not be performed in patients with an unrepaired tracheoesophageal fistula, esophagectomy, perforated viscus, or active gastrointestinal bleed. A history of esophageal varices is not an absolute contraindication to TEE; however, the small risk of major bleeding needs to be weighed against the potential for important incremental information. A severe coagulopathy is a relative contraindication to TEE; however, TEE can safely be performed in patients on anticoagulation therapy. Severe cervical arthritis or dislocation of the atlantoaxial joint, where neck flexion is severely limited, is a relative contraindication.

Complications of Transesophageal Echocardiography

TEE is a relatively safe procedure with a low risk of serious complications. In up to 1.9% of TEE studies, the esophagus cannot be successfully intubated.¹⁹³ Procedural complications occur in up to 3.5% of patients and predominantly involve the gastrointestinal, cardiovascular, or respiratory systems.¹⁹³ The vast majority of complications are minor (Box 1-4), with approximately 0.2% to 0.5% of patients suffering a major complication.^5,^9,^193,¹⁹⁴ TEE-related mortality has been estimated at less than 0.01%.¹⁹⁴ A recent review of 17 studies encompassing 42,355 patients identified four TEE procedural deaths.¹⁹³

Perforation of the esophagus and major upper gastrointestinal bleeding are serious gastrointestinal complications that occur in up to 0.01% and 0.03% of TEE studies, respectively.¹⁹⁴ Minor gastrointestinal complications include lip and pharyngeal bleeding due to mucosal trauma and excessive retching or vomiting that can require premature termination of the examination.⁹ Dental injuries occur in up to 0.03% of patients.¹⁹⁴ A minor sore throat may be present for 24 hours after the procedure. Approximately 0.1% of patients have persistent odynophagia that requires further investigation.¹⁹⁴

Cardiac complications are rare and include nonsustained and sustained supraventricular tachycardias or atrial fibrillation, nonsustained and sustained ventricular tachycardia, bradycardia, transient hypotension or hypertension, angina pectoris, congestive heart failure, and pulmonary edema.^193,¹⁹⁴

Respiratory complications include laryngospasm (less than 0.02%), accidental tracheal intubation, transient hypoxia, and blood-tinged sputum.^193,¹⁹⁴

Adverse reactions may occur from intravenous sedation or topical anesthesia. Intravenous sedation can cause respiratory depression, hypoxia, hypotension, or paradoxical reactions. Topical anesthesia with benzocaine or lidocaine can cause acute toxic methemoglobinemia, a rare but potentially lethal condition that manifests clinically in approximately 0.115% of TEE studies.¹⁹⁵ In this condition, the topical anesthesia agent oxidizes hemoglobin and prevents oxygen delivery to the tissues, potentially resulting in cyanosis, lethargy, tachycardia, dyspnea, and death.¹⁹⁵^–¹⁹⁷ Methylene blue administration is indicated if the methemoglobin levels are above 30%, or if the patient has cyanosis, central nervous system depression, or cardiopulmonary compromise.¹⁹⁵

Intraoperative TEE has a morbidity rate of 0.2% to 1.2%, similar to that reported in the nonoperative setting.¹⁹⁴ The complication rates for TEE in pediatric patients are variable.¹⁹⁴ The largest case series of predominantly intraoperative TEE reported a complication rate of 2.4% (excluding failed intubations).¹⁹⁸

Key Points

TTE and TEE are complementary modalities with distinctly different advantages and limitations for the evaluation of patients with suspected cardiac disease.