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Transesophageal Echocardiography

Step-By-Step Approach

Step 1: Clinical Data

1. ▪ In addition to the indication for the study and the cardiac history, clinical data establishing the safety of the transesophageal echocardiography (TEE) procedure are needed.
   
2. ▪ The risk of the TEE procedure is related to both moderate sedation and esophageal intubation.
   
3. ▪ Informed consent is obtained before the procedure.

Key Points

• □ Informed consent includes a description of the procedure with explanation of the expected benefits and potential risks.
  
• □ Complications serious enough to interrupt the procedure occur in less than 1% of cases, and the reported mortality rate is less than 1 in 10,000.
  
• □ Significant esophageal disease, excessive bleeding risk, and tenuous respiratory status are contraindications to TEE.
  
• □ The risk of hemodynamic compromise and respiratory depression are assessed using standard pre-anesthesia protocols and risk levels.
  
• □ Risk is higher in patients with impaired respiratory status or a history of sleep apnea.
  
• □ Patients typically have no oral intake for at least 6 hours before the procedure, except in emergencies.
  
• □ In anticoagulated patients, the level of anticoagulation is checked before the TEE to ensure it is in the therapeutic range.

Step 2: TEE Protocol

1. ▪ The moderate sedation standards at each institution apply to TEE procedures.
   
2. ▪ Typically, these include having a credentialed health care provider monitor level of consciousness, blood pressure, electrocardiogram, and arterial oxygen saturation.
   
3. ▪ Oral suction is used to clear secretions and maintain an open airway.
   
4. ▪ The study is optimally performed with a physician to manipulate the probe and direct the examination, a cardiac sonographer to optimize image quality and record data, and a nurse to monitor the patient.

Key Points

• □ Adequate local anesthesia of the pharynx improves patient comfort and tolerance.
  
• □ The specific choice and dose of pharmacologic agents for sedation are based on institutional protocols.
  
• □ Endocarditis prophylaxis is not routinely recommended for TEE.
  
• □ The TEE probe is inserted via a bite block using ultrasound gel for lubrication and to provide acoustic coupling between the ultrasound transducer and the wall of the esophagus.
  
• □ The TEE probe is advanced and diagnostic images are obtained in standard image planes by turning the probe and rotating the image plane (Fig. 3.1).
  
• □ All health care providers involved in the procedure use universal precautions to prevent exposure to body fluids.

Step 3: Basic Examination Principles

1. ▪ Although the TEE study is directed toward answering the clinical question, a complete systemic examination is recorded unless precluded by the clinical situation.
   
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3. ▪ Standard tomographic planes are used to evaluate cardiac chambers and valves with side-by-side, simultaneous display of orthogonal imaging planes (90° offset) when needed.
   
4. ▪ The structure or flow of interest is centered in the image plane with depth and sector width adjusted to optimize image quality.
   
5. ▪ Three-dimensional (3D) imaging using real-time zoom mode and acquisition of full volume 3D datasets is used for measurement of left ventricular (LV) volumes and ejection fraction and for visualization of mitral valve anatomy.
   
6. ▪ Additional 3D imaging is based on the clinical diagnosis and two-dimensional (2D) imaging findings.

Key Points

• □ In stable patients, a complete TEE examination is recommended with recording of all standard image planes and Doppler flows.
  
• □ In unstable patients, the examination should focus on the key diagnostic issues first, with additional recordings as tolerance and time allow.
  
• □ Each cardiac structure is evaluated in at least two orthogonal views or, ideally, using a rotational scan of the structure.
  
• □ The structure of interest is centered in the image plane with transducer frequency, depth, and zoom adjusted to optimize visualization.
  
• □ With color Doppler, frame rate is optimized by decreasing depth and sector width to focus on the flow of interest.
  
• □ Only one to two beats of each view are recorded so that the examiner can move quickly through the examination sequence. The total intubation time for a complete TEE ranges from less than 10 minutes for a relatively normal study to up to 30 minutes for complex examinations.

Step 4: Imaging Sequence

1. ▪ The basic imaging sequence suggested in the Echo Exam Basic Transesophageal Echocardiography Exam Sequence table at the end of this chapter is organized by probe position, because this is the most efficient approach to examination in most cases.
   
2. ▪ The imaging sequence is adjusted to focus on the key issues in unstable patients.
   
3. ▪ This step-by-step approach describes the evaluation of each anatomic structure. This evaluation often is incorporated into the standard exam sequence shown in the Echo Exam table.

Key Points

• □ The probe position is constrained by the position of the esophagus so that optimal views are not always possible.
  
• □ The terms advance and withdraw refer to the vertical motion of the probe in the esophagus and stomach (Fig. 3.2).
  
• □ The term turn refers to manual rotation of the entire probe toward the patient’s right or left side.
  
• □ The terms flexion and extension refer to motion of the tip of the probe in a plane parallel to the long-axis of the probe, controlled by a large dial at the base of the probe (Figs. 3.3 and 3.4).
  
• □ The term rotation refers to the electronic movement of the image plane in a circular fashion, controlled by a button on the probe and displayed as an angle on the image (Fig. 3.5).
  
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• □ The exact degree of rotation needed for a specific view varies from patient to patient, depending on the relationship between the heart and esophagus. The values given here are a starting point; image planes are adjusted based on cardiac anatomy, not specific rotation angles.
  
• □ If a specific view or flow is difficult to obtain, continue with the examination and return to this view later in the study.
  
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• □ The specific views and flows recorded depend on the clinical indication and the findings of the study.
  
• □ Although modification of the exam sequence often is necessary, the examiner should quickly review a checklist of the recorded data before removing the probe to ensure a complete exam.

Step 5: Left Ventricle

1. ▪ The LV is evaluated in the mid-esophageal 4-chamber, 2-chamber, and long-axis views.
   
2. ▪ A 3D full-volume image dataset of the LV is obtained from a mid-TEE position for measurement of LV volumes and ejection fraction.
   
3. ▪ Additional views of the LV include the transgastric short-axis view and the transgastric apical view.

Key Points

• □ The starting point for a TEE is a 4-chamber view recorded from a mid-esophageal position (0° rotation) at maximum depth to show the entire LV. Typically the probe is extended to include as much of the apex as possible (Fig. 3.6).
  
• □ With the probe centered behind the left atrium (LA) and the LV apex in the center of the image, the image plane is rotated to about 60° to obtain a 2-chamber view and then rotated further to about 120° for a long-axis view, followed by a multi-beat full volume 3D acquisition.
  
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• □ The transducer position, angulation, and exact degree of rotation are adjusted to optimize each view.
  
• □ Regional ventricular function is evaluated as follows:
  
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  • □ Lateral wall and inferior septum in the 4-chamber view
    
  • □ Anterior and inferior walls in the 2-chamber view
    
  • □ Anterior septum and the inferior-lateral (or posterior) wall in the long-axis view
  
  
• □ Quantitative ejection fraction measurements are made using the 3D full-volume acquisition with automated border detection or the 2D biplane approach with tracing of endocardial borders at end-diastole and end-systole in 4-chamber and 2-chamber views (Fig. 3.7).
  
• □ An apical LV thrombus may be missed, because the apex is in the far field of the TEE image; transthoracic imaging is more sensitive for detection of apical thrombus.

Step 6: Left Atrium and Atrial Septum

1. ▪ The body of the LA is evaluated in the mid-esophageal 4-chamber, 2-chamber, and long-axis views.
   
2. ▪ The LA appendage is imaged in at least two orthogonal planes at 0° and 90° using the biplane mode or rotating between image planes.
   
3. ▪ 3D imaging of the LA appendage is helpful in selected cases for thrombus detection or procedural planning.
   
4. ▪ The pulmonary veins are identified using 2D and color Doppler imaging most easily in the 0° image plane, although views at 90° also may be helpful.

Key Points

• □ Images of the LA are recorded at a shallow depth to focus on the structure of interest.
  
• □ The atrial septum is best examined by centering the septum in the image plane in the 4-chamber view and then slowly rotating the image plane, keeping the septum centered, from 0° to 120° (Fig. 3.8). A 3D volumetric image also can be recorded.
  
• □ The atrial appendage is imaged using a high frequency transducer, zoom mode, and a narrow sector to improve image resolution (Fig. 3.9). Simultaneous biplane imaging of the LA appendage or sequential images in a rotational scan are recommended for detection of LA appendage thrombus.
  
• □ Flow in the atrial appendage is recorded with a pulsed Doppler sample volume about 1 cm from the mouth of the appendage (Figs. 3.10 and 3.11).
  
• □ The pulmonary veins are most easily identified using color Doppler with the aliasing velocity decreased to about 20 to 30 cm/s.
  
• □ The left superior pulmonary vein (LSPV) is located adjacent to the atrial appendage and enters the atrium in an oblique anterior to posterior direction.
  
• □ The left inferior pulmonary vein, seen by advancing the probe a few centimeters, enters the atrium in a left lateral to medial direction (Fig. 3.12).
  
• □ The right pulmonary veins are imaged in the 0° plane by turning the probe toward the patient’s right side.
  
• □ The superior vein enters the atrium in an anterior–posterior direction; the inferior vein is seen by advancing the probe and enters in a right lateral to medial direction (Fig. 3.13).
  
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• □ Pulmonary vein flow is recorded with pulsed Doppler in one or more pulmonary veins, depending on the clinical indication for the study (Fig. 3.14).
  
• □ An orthogonal view at 90° also may be helpful, turning the probe rightward for the right pulmonary veins and leftward for the left pulmonary veins (see Figs. 3.12 and 3.13).

Step 7: Mitral Valve

1. ▪ The mitral valve is evaluated starting in the 4-chamber view and then rotating the image plane slowly to 120° (long-axis view), keeping the valve centered in the image.
   
2. ▪ Additional views of the mitral valve include the transgastric short-axis and 2-chamber view.
   
3. ▪ 3D imaging of the mitral valve is recommended in most patients, particularly for myxomatous mitral valve disease, other leaflet abnormalities, or annular dilation.
   
4. ▪ TEE provides optimal evaluation of mitral regurgitant severity, allowing a parallel angle between the flow direction and ultrasound beam for continuous-wave (CW) Doppler, excellent visualization of the jet origin and direction, and accurate measurement of vena contracta width and proximal isovelocity surface area (PISA) radius.

Key Points

• □ The image depth is adjusted to just fit the mitral valve on the image. Transducer frequency, harmonic imaging, and gain are adjusted to improve the image (Fig. 3.15).
  
• □ The mitral valve is first evaluated with 2D imaging alone to focus on the details of valve anatomy.
  
• □ 3D real-time zoom and full volumes imaging are recommended when the valve is abnormal (Fig. 3.16).
  
• □ A second rotational scan is performed using color Doppler to evaluate for mitral regurgitation. Regurgitation is evaluated based on measurement of the vena contracta, evaluation of pulmonary venous flow pattern, the CW Doppler signal, and quantitative parameters, as discussed in Chapter 12 (Fig. 3.17).
  
• □ Simultaneous split screen 2D and color imaging shortens the exam time, but eccentric jets might be missed due to the narrower sector width compared to full screen imaging.
  
• □ The transgastric view of the mitral valve offers improved visualization of the subvalvular apparatus, although concurrent evaluation by transthoracic imaging also may be needed.

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1. Specialized Echocardiography Applications
2. Intraoperative and Interventional Echocardiography
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4. Valvular Regurgitation

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