To maximize the diagnostic yield from transesophageal echocardiography (TEE), it is important to have an understanding of standard imaging views and important anatomic–echocardiographic relationships. Echocardiography is most commonly a two-dimensional (2-D) representation of three-dimensional (3-D) structures, and it is difficult (and frequently misleading) to make functional assessments without adequate views in multiple planes. Furthermore, unanticipated pathology may easily be missed. Therefore, if time and resources permit, a comprehensive TEE examination should be performed on every patient. This should be done in a systematic way to ensure that all major structures are identified and evaluated appropriately. Performing a complete examination also increases experience, which is essential for distinguishing normal variants from pathologic states. If time is limited, the primary area of interest should be examined in as much detail as possible and a limited review of the remaining structures should be undertaken.
The following descriptions owe much to the significant contribution by the American Society of Echocardiography (ASE) and the Society of Cardiovascular Anesthesiologists (SCA), which appointed a task force to develop guidelines for performing a comprehensive, intraoperative, multiplane TEE examination. With a few explicitly identified exceptions, the standard views and nomenclature recommended in the ASE/SCA guidelines are used throughout this book.
The orientation of the heart and its relationship to the TEE transducer varies from patient to patient, and the cardiac structures may be distorted by pathology. Therefore, probe–transducer positions and angles are given as general guides only.
Specific structures, such as the mitral valve (MV) or segmental left ventricular (LV) wall motion, are described in detail in the relevant chapters, as is the use of more advanced techniques, such as 3-D echocardiography.
Throughout this chapter, the term probe refers to the modified gastroscope and the term transducer refers to the active scanning elements housed in the tip of the probe.
Probe preparation, probe placement, and image quality
A modern adult TEE probe is a modified gastroscope suitable for use in patients weighing more than 55 lbs (25 kg). The probe should be chemically sterilized and free from defects (see Appendix 2 ).
Inserting the probe into an intubated, anesthetized patient is usually straightforward. If teeth are present, a dental guard should be used to protect teeth and the probe. The flexion control lock should be disengaged before insertion and removal of the probe. Liberal lubrication of the tip and gentle anterior thrust of the mandible usually allow blind placement of the probe. While a mild degree of resistance is usually experienced as the probe passes the upper esophageal sphincter, excessive force must not be used. Occasionally, modest anteflexion of the tip assists passage within the mouth and slight retroflexion may facilitate entry into the esophagus. A laryngoscope may be useful if difficulty is encountered.
Image quality with TEE is generally good, but it is rare for every individual view to be of high quality in a particular patient. Contact of the transducer with the diaphragmatic surface of the stomach is necessary for adequate transgastric imaging, but this may be impossible in a patient with a diaphragmatic hernia. If image quality is poor, it may help to remove the probe, cover it well in gel, suction air from the stomach, and reinsert the probe. A nasogastric feeding tube may prevent adequate contact between the transducer and the esophageal wall, so the feeding tube should be removed before starting the examination. As surgical diathermy reduces image quality, particularly for Doppler assessments, it is preferable to complete the pre–cardiopulmonary bypass (CPB) study as soon as possible after induction of anesthesia.
Because of the orientation of the esophagus and trachea to the cardiac structures, some regions of interest are difficult or impossible to image with TEE. In particular, the distal ascending aorta and proximal aortic arch may not be seen, and complete transgastric visualization of the LV apex is unreliable. It may be impossible to adequately align a continuos wave (CW) Doppler signal through the aortic valve (AV).
Movements of the probe
The probe can be manipulated in a number of ways to facilitate image acquisition ( Figure 3-1 ). The movements described here are made with reference to an echocardiographer standing at a patient’s head looking toward the feet.
The shaft of the probe may be advanced into or withdrawn from the esophagus and turned to the right (clockwise) or to the left (anticlockwise). The tip of the probe may be anteflexed (anteriorly) or retroflexed (posteriorly) by rotating the large control wheel on the handle of the probe. Rotating the small control wheel flexes the tip of the probe to the left or to the right, although with the advent of multiplane TEE transducers this manipulation is rarely necessary.
Rotation of the transducer refers to movement of the sector scan from 0 to 180 degrees:
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At 0 degrees, the sector scan lies in the transverse image plane and runs perpendicular to the shaft of the probe.
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At 90 degrees, the sector scan lies in the longitudinal or vertical plane and runs parallel to the shaft of the probe.
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At 180 degrees, the view is a mirror image of the view at 0 degrees.
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At 45 degrees, the plane of the sector scan runs between the left shoulder and the right leg.
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At 135 degrees, the plane of the sector scan runs between the right shoulder and the left leg.
Movement of the sector scan in the direction of 0 to 180 degrees is called rotating forward; movement of the sector scan in the direction of 180 to 0 degrees is called rotating backward.
Esophageal trauma may result from TEE, so probe movements should be kept to the minimum necessary. Insertion or withdrawal of the probe should not be performed when the control wheels are locked (see Figure 3-1 ).
The standard sector display
The apex of the sector scan is shown at the top of the screen and locates the posterior cardiac structures (i.e., those closest to the transducer). In the transverse image plane (0-degree rotation), the left of the image is toward the patient’s right, and the right of the image is toward the patient’s left. In the vertical image plane (90-degree rotation), the left side of the image is inferior and points toward the patient’s feet and the right side of the image is anterior and points toward the patient’s head ( Figure 3-2 ).
Centering the image
Once a structure of interest has been centered within one image plane, it remains in the center of successive image planes as the transducer is rotated between 0 and 180 degrees. This greatly facilitates the 3-D assessment of any particular structure.
To center a structure in the transverse image plane (0-degree rotation), the shaft of the probe should be turned to the left or to the right so that the structure of interest is aligned in the middle of the display. If the transducer is in the vertical image plane (90-degree rotation), advancing or withdrawing the probe will achieve the same result.
The doppler mode display
A Doppler signal can be used to measure the velocity of moving blood or tissue in relation to the position of the ultrasound transducer (see Chapter 3), for example, for assessing pressure gradients across stenotic lesions, ventricular diastolic function, or the severity of valvular regurgitation.
When using CW, pulse wave (PW), or tissue Doppler (i.e., spectral Doppler) imaging modes, a line appears on the standard sector 2-D display, which can be steered to overlie the area to be measured. In PW or tissue Doppler mode, a sample volume appears, which can be moved up and down the line to interrogate a specific depth of interest. Although display formats vary across platforms, the basic layout for spectral Doppler is similar (see Figures 2-2 , 2-3 , and 2-5 ). A small 2-D sector is displayed at the top of the screen to indicate the direction of the Doppler beam (and the location of the sample volume in PW and tissue Doppler modes). The lower part of the display shows a plot of velocity against time, with velocity (usually in centimeters or meters per second) on the y-axis and time on the x-axis. By convention, flow away from the transducer is recorded below the baseline and toward the transducer above the baseline. Both the time and the velocity scales can be altered, although adjustments of the velocity scale are more common. It is also possible to adjust the Doppler gain and the baseline position of the plot. Gain should be adjusted until background “noise” in the display is minimal or absent, although occasionally with weak signals (or a low signal-to-noise ratio) it may be necessary to increase the gain for the signal to be seen, even at the expense of a less clear display. The baseline should be adjusted to ensure that the full velocity envelope is displayed on the screen (compare Figures 2-3 and 2-5 ). The position of the transducer, the sector scan, the Doppler beam, or a combination of these needs frequent adjustment to optimize the waveform. Audio may also be used in helping to locate the strongest signal. Once the best waveform has been obtained, the display should be frozen for further analysis.
With color flow Doppler, an adjustable color window (map) is superimposed on a 2-D sector display. Both the size and the position of the color map can be adjusted (see Figure 3-2 ). Narrowing the color window enables a higher frame rate, while decreasing its depth increases both frame rate and pulse repetition frequency, thereby also increasing the Nyquist limit (see Chapter 2 ), which allows a higher velocity to be recorded without aliasing. Color gain should be adjusted to avoid color speckling of background objects in the sector window. Color scale and baseline can also be adjusted to minimize aliasing.
Standard views and systematic examination
Before starting an examination, the recording media should be cued if digital acquisition is not being used, the patient details entered, and the machine controls adjusted for optimal resolution (these may need further adjustment during the examination). In particular, adjust the following:
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2-D gain so that the chambers are black while the tissues remain white–gray.
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Color gain to a level just below that which produces background noise and speckling.
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Sector depth to optimize the view of the structures being assessed. This is usually between 6 and 16 cm; the aorta is usually best seen at 6 cm.
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Focus to just beyond the structure of interest.
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TGC and LGC (if available).
The terms short axis and long axis are used throughout the following sections. Generally, short axis refers to an image plane perpendicular to the structure of interest, and long axis refers to an image plane parallel to the length of the structure of interest. With respect to the left ventricle, the term long axis has a specific meaning: it applies to any image plane in which both the aortic valve (AV) and the mitral valve (MV) can be seen simultaneously. Because of the orientation of the heart, many structures are seen in short axis in (or close to) the transverse (0-degree) image plane and in long axis in (or close to) the longitudinal (90-degree) image plane. However, this is not always the case—notably, for the aortic arch.
Images are collected at four depths: upper esophageal (20-30 cm), midesophageal (30-40 cm), transgastric (40-45 cm), and deep transgastric (45-50 cm). The great majority of images are obtained at the midesophageal and transgastric levels.
The midesophageal views fall into two convenient groups: the midesophageal aortic views and the midesophageal ventricular views. The aortic views are slightly higher than the ventricular views, and the midesophageal five-chamber view provides a useful link between these two levels. The ASE/SCA recommends 20 standard images for a systematic TEE examination; these are described later. Various other views are in common usage, notably the five-chamber view and the views of the coronary sinus, pulmonary and hepatic veins, and pleural spaces.
The views used in assessing each of the major cardiac structures are summarized in Table 3-1 . Normal dimensions and velocities are given in Appendix 3 .
| View | Key Structures and Assessments |
|---|---|
| Aortic Valve | |
| ME AV SAX | En face view of all three leaflets, CF Doppler for aortic regurgitation |
| ME AV LAX | Noncoronary (or possibly left) and right cusps, root measurements, CF Doppler for aortic regurgitation |
| Deep TG LAX | CW and PW Doppler through AV and LVOT |
| TG LAX | CW and PW Doppler through AV and LVOT |
| Left Ventricle | |
| ME four-chamber | Inferoseptal and anterolateral walls (basal, middle, apical levels) |
| ME two-chamber | Inferior and anterior walls (basal, middle, apical levels) |
| ME LAX | Inferolateral (posterior) and anteroseptal walls (basal, middle levels) |
| TG basal SAX | All segments at basal level |
| TG mid-SAX | All segments at midlevel, fractional area change, volume status |
| TG two-chamber | Inferior and anterior wall (basal and middle levels) |
| Mitral Valve | |
| ME four-chamber | A2/P2 segments, LA dimension, CF Doppler for mitral regurgitation |
| ME commissural | P3/A2/P1 segments, CF Doppler for mitral regurgitation |
| ME two-chamber | P3/A3, A2, A1 segments, CF Doppler for mitral regurgitation |
| ME LAX | P2/A2 segments, annular size, leaflet length, CF Doppler for mitral regurgitation |
| TG basal SAX | En face view of all leaflet segments with CF Doppler |
| TG two-chamber | MV subvalvular apparatus |
| Right Ventricle and Atrium, Tricuspid and Pulmonary Valves | |
| ME four-chamber | Lateral free wall, septal and posterior tricuspid leaflets, CW Doppler for tricuspid regurgitation |
| ME coronary sinus | Coronary sinus |
| ME RV inflow–outflow | Inferior free wall, RVOT, posterior and anterior tricuspid leaflets, CF Doppler of PV, CW Doppler for maximum tricuspid regurgitant velocity |
| TG RV inflow view | TV subvalvular apparatus |
| Ascending Aorta and Pulmonary Artery | |
| ME ascending aortic SAX | Proximal ascending aorta, velocity–time integral through main pulmonary artery |
| ME ascending aortic LAX | Proximal ascending aorta |
| ME RV inflow–outflow | PV |
| Interatrial Septum and Vena Cavae | |
| ME four-chamber | Fossa ovalis, patent foramen ovale, CF Doppler across atrial septum |
| ME bicaval | Fossa ovalis, patent foramen ovale, eustachian valve, CF Doppler across atrial septum |
| Descending Thoracic Aorta | |
| Descending aortic SAX | Left pleural effusion |
| Descending aortic LAX | PW Doppler flow in descending aorta |
| Upper esophageal aortic arch LAX | Distal arch |
| Upper esophageal aortic arch SAX | Distal arch, origin of left subclavian artery |
Midesophageal aortic views
The midesophageal aortic views are useful for assessing the AV and the proximal ascending aorta. Two additional views are also obtained at this level: the midesophageal right ventricular (RV) inflow–outflow view, which is used for assessing the right ventricle and tricuspid valve (TV), and the midesophageal bicaval view, which is used for assessing the atrial septum and vena cavae.
Midesophageal five-chamber view (0 degrees)
The five-chamber view ( Figure 3-3 ) is easy to obtain and serves as a convenient starting point. With the sector scan at 0 degrees, the probe is advanced into the esophagus 35 to 40 cm until the AV is seen in oblique cross section. The five chambers are the right atrium, right ventricle, left atrium, left ventricle, and left ventricular outflow tract (LVOT).
Midesophageal aortic valve short-axis view (40 degrees)
To obtain a true short-axis view of the AV ( Figure 3-4 ), the probe is withdrawn slightly from the five-chamber view with the AV centered and the transducer is rotated (to 40 degrees) until the characteristic three leaflets of the AV are seen in short axis (the “Mercedes-Benz sign”). The noncoronary cusp lies adjacent to the atrial septum (on the left of the display), the right coronary cusp is the most anterior (lowermost on the display—recall that, during cardiac surgery, intra-aortic air usually enters the right coronary artery), and the left coronary cusp is seen on the right of the display.
The probe may be withdrawn slightly to visualize the origins of the coronary arteries.
Midesophageal aortic valve long-axis view (130 degrees)
From the short-axis view of the AV, the transducer is rotated (through 90 degrees) to approximately 130 degrees to obtain a long-axis view of the AV ( Figure 3-5 ). The probe is turned right and left until leaflet excursion is clear and the aortic root is seen clearly in long axis. The right coronary cusp is the most anterior of the three cusps and is therefore seen lowermost on the display, adjacent to the right ventricular outflow tract (RVOT). The cusp seen adjacent to the anterior mitral leaflet is either the noncoronary (usually) or the left coronary cusp (the association between the anterior mitral leaflet and the AV is useful when trying to identify which mitral leaflet is seen in a particular view).
An echo-free structure caused by fluid in the transverse pericardial sinus is sometimes seen between the posterior wall of the ascending aorta and the left atrium. If fluid has collected behind the heart, the oblique pericardial sinus may be seen between the posterior wall of the left atrium and the esophagus (from any midesophageal view). In this view, pericardial effusions are often identifiable between the RV free wall and the pericardium.
Midesophageal ascending aortic short-axis view (40 degrees)
From the five-chamber view, the transducer is rotated to 40 degrees and the probe is withdrawn until the short-axis view of the ascending aorta is seen ( Figure 3-6 ). This view shows the proximal ascending aorta, main pulmonary artery, right pulmonary artery, and the superior vena cava (SVC). As the probe is progressively withdrawn, the main pulmonary artery, which is initially seen as a circle, becomes oval as it curves posteriorly (toward the transducer) before branching into the left and right pulmonary arteries. At this level, the aorta is separated from the transducer by the right pulmonary artery, not the left atrium.
