Two-Dimensional Examination

Joseph P. Miller

ECHOCARDIOGRAPHY IS A CORNERSTONE OF medical imaging and clinical decision making. Echocardiographic technology continues to rapidly improve. Real-time biplane imaging is a reality in most systems and live 3D image acquisition is more common. These newer technologies are playing a real role in intraoperative clinical decision making. However, 2D imaging remains the fastest, most reproducible means of rapidly making clinical echocardiographic-based decisions and impacting clinical care in the operating room. In 2013, the most recent guidelines for performing a comprehensive transesophageal echocardiographic examination (TEE) outlined 28 echo views that will provide a complete picture of cardiac and major intrathoracic vascular structures (1). This article builds on the original paper from 1999 and increases the focus from simple image descriptions (2). Although the current comprehensive guidelines offer a thorough description of terminology, 2D, biplane, and 3D imaging techniques, it can be difficult to follow for the novice echocardiographer.

The purpose of the fourth edition of this chapter is to demystify echocardiographic image orientation and provide the stepwise approach to image acquisition. This chapter will focus on basic terminology, 2D image orientation, and techniques to rapidly obtain clinically useful echocardiographic images.

PROBE MANIPULATION

The probe manipulation terminology has changed little from the 1999 guidelines. The position and orientation of the TEE probe can be altered by several types of manipulation (Fig. 2.1A). By gripping the probe shaft near its entrance in the mouth, the probe can be advanced or withdrawn. The degree of insertion can be easily determined by the depth markings imprinted on the shaft. For cardiac imaging, the probe position ranges from the upper esophagus (UE) to the stomach. In the UE, the structure closest to the TEE probe is one of the great vessels. In the midesophagus (ME), the structure closest to the TEE probe is the left atrium, and in the transgastric (TG) position, the structure closest to the TEE probe is the left or right ventricle. In the deep gastric (DG) position, the closest structure is the left ventricle (Fig. 2.1B). Therefore, depending on the depth of insertion, the structure at the apex of the imaging sector will be one of the great vessels, the left atrium, the left or right ventricle. This concept is especially important when new to echocardiographic imaging.

The orientation of the ultrasound beam can be further adjusted by manually turning the probe shaft to the left, counterclockwise, or right, clockwise. (1999 guidelines left and right; 2013 guidelines counterclockwise and clockwise.) The probe can be anteflexed or retroflexed by using the large knob on the probe handle. The small knob on the probe handle will flex the probe leftward or rightward. These maneuvers allow precise user control over the direction of the ultrasound beam to visualize the structure of interest.

MULTIPLANE IMAGING ANGLE

Understanding the orientation of the imaging plane is crucial for both acquisition of the desired images and correct interpretation of the displayed cardiac anatomy. Although TEE is limited to the confines of the esophagus and stomach, the ability to alter the position and orientation of the ultrasound beam allows a broad view of the cardiac anatomy.

The first clinically useful TEE probes were capable of producing a single or monoplane cross-section of the heart. This imaging plane is generated perpendicular to the shaft of the probe and corresponds to the typical transverse views obtained with transthoracic echocardiography. The biplane probes of the next generation were able to produce two perpendicular views: the standard transverse cross-section and a longitudinal cross-section. Currently, most of the probes in use in adult TEE are multiplane probes. Through an electronic switch on the probe handle, the operator selectively rotates the orientation of the imaging plane from 0° (transverse plane) through 180° in 1° increments. The rotation of the imaging
plane is depicted in

Video 2.1. This capability offers many advantages with respect to image acquisition but can also generate tremendous confusion for novice echocardiographers.

FIGURE 2.1 A: Terminology used to describe manipulation of the probe and transducer during image acquisition. B: Four standard transesophageal probe positions for cardiac imaging. (From Hahn RT, Abraham T, Adams MS, et al. Guidelines for performing a comprehensive transesophageal echocardiographic examination: Recommendations from the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists. J Am Soc Echocardiogr 2013;26:921-964, with permission.)

Experts rely on two key points to determine image orientation quickly. First, independent of the imaging plane, the ultrasound beam always originates from the esophagus or stomach and projects perpendicular to the probe. Consequently, on the monitor, the apex of the sector displays structures that are closest to the TEE probe. As a general rule of thumb, structures seen near the apex of the image sector (i.e., closest to the TEE probe) will be posterior structures, and those close to the arc of the sector (i.e., more distant from the TEE probe) will be anterior structures.

Second, left, and right orientation depends on the degree of rotation of the scan head. A simple way to orient yourself is to place your right hand at your chest with your palm facing downward, your extended thumb pointing leftward and anterior, and your fingers rightward and anterior. This is the orientation of the imaging scan at 0° and the scan lines begin at your fingers sweeping right-to-left toward your thumb. Consequently, your fingers point toward right heart structures that will be displayed on the left side on the monitor as you look at the screen (Fig. 2.2). Note that this right-to-left display orientation is similar to that of a chest x-ray.

Increases in the imaging plane angle proceed in a clockwise manner. For example, when the imaging plane is rotated to 90°, the imaging orientation is mirrored by rotating your hand clockwise 90° (fingers pointing downward) (Fig. 2.3).

The combination of probe manipulation and altering the imaging plane angle provides a powerful tool for cardiac imaging (Fig. 2.4). For example, slight withdrawal of the probe and rotation of the imaging plane to 40° provides a short-axis view of the aortic valve (Fig. 2.5). In contrast, advancement of the probe into the stomach combined with anteflexion and rotation of the imaging plane to 0° provides a short-axis view of the left ventricle (Fig. 2.6).

Once you have a solid understanding of probe manipulation and basic imaging angle orientation, the next step in understanding image orientation is to visualize how your imaging sector cuts through the base of the

heart. This is especially important for atrioventricular valve leaflet identification. (Fig. 2.7) With this new understanding you are ready to begin your TEE examination.

FIGURE 2.2 A: Orientation of your hand, as described in text, for an imaging plane of 0°. The red and green lines correspond with the lines described in Figure 2.2B. B: The top figure is a schematic representation of a transesophageal echocardiography (TEE) probe obtaining a midesophageal (ME) four-chamber view. The TEE probe lies in the esophagus posterior to the left atrium. The imaging plane is projected like a wedge anteriorly through the heart. The image is created by multiple scan lines traveling back and forth from the patient’s left (green edge of imaging sector) to the patient’s right (red edge). The resulting image is displayed on the monitor with the green edge of the sector displayed on the right side of the monitor and the red edge on the left. In the bottom image, the schematic is made transparent and the anatomy of the heart is displayed in the orientation seen in a ME four-chamber view.

FIGURE 2.3 A: Orientation of your hand, as described in text, for an imaging plane of 90°. The red and green lines correspond with the lines described in Figure 2.3B. B: The top figure is a schematic representation of a transesophageal echocardiography (TEE) probe obtaining a midesophageal (ME) two-chamber view. The probe is in the same position as described in Figure 2.2. However, in this case the imaging sector is rotated so that the green sector edge has moved clockwise and is now cephalad, and the red sector edge is now caudad. As previously described, the green edge is displayed on the right side of the monitor’s screen and the red edge on the left. In the bottom image, the schematic is made transparent and the anatomy of the heart is displayed in the orientation seen in a ME two-chamber view.

FIGURE 2.4 Through simple manipulations, the transesophageal echocardiography (TEE) probe offers a multifaceted picture of cardiac anatomy. Progressive advancement of the probe in the midesophagus provides a cross-sectional view of the aortic valve (A) followed by a long-axis view of the cardiac chambers (B) Further advancement and anteflexion of the probe head (C) allows visualization of the left ventricle in the short-axis. Rotation of the imaging plane expands the imaging capacity of TEE. In this example, the left ventricle and its outflow tract are brought into view by rotating the imaging plane to 120°. LA, left atrium; RA, right atrium; N, noncoronary cusp; L, left coronary cusp; R, right coronary cusp; RV, right ventricle; LV, left ventricle; Ao, aorta.

PROBE INSERTION

The TEE probe is passed into the esophagus in the same manner in which an orogastric tube is placed. The easiest way to insert the probe is to perform a jaw lift by grabbing the mandible with the left hand and inserting the probe with the right. Be aware that the fine print with most systems states that a bite block should be placed before passing the probe. This is required to protect the shaft of the probe from the teeth or gums. Performing a jaw lift with the bite block in place will facilitate probe placement. If there is difficulty with probe passage, remove the bite block from the mouth, perform the jaw lift, insert the probe and then slide the bite block down the probe into the proper position. The probe is inserted with constant gentle pressure in addition to a slight turning back and forth and from left-to-right to find the esophageal opening. If resistance is encountered, the cause most often is excessive extension of the head and neck. Advancement of the probe is stopped after the head of the probe has passed the larynx and cricopharyngeus muscle, where a distinct loss of resistance is felt. A laryngoscope is rarely needed when the described procedure is followed. When using a laryngoscope, insert the scope and try to visualize the posterior laryngeal apparatus and view the TEE probe going directly behind the posterior cricoarytenoid muscle into the trachea. The imaging head will then lie in the UE.

FIGURE 2.5 The top figure is a schematic representation of a transesophageal echocardiography (TEE) probe obtaining a midesophageal (ME) aortic valve short-axis view. The probe is in the esophagus is but slightly above the position in Figures 2.2 and 2.3. When the leaflets of the aortic valve are seen, the imaging plane is rotated from 0° to approximately 40° when the aortic valve is seen in a true cross-section. The image on the monitor is generated from scan lines going back and forth from the green edge (right side of monitor) to the red edge (left side of monitor). In the bottom image the schematic is made transparent and the anatomy of the heart is displayed in the orientation seen in a ME aortic valve short-axis view.

FIGURE 2.6 The top figure is a schematic representation of a transesophageal echocardiography (TEE) probe obtaining a transgastric (TG) midpapillary short-axis view. The probe is advanced in to the stomach and anteflexed until solid contact is made with the gastric wall. The imaging plane is projected from the probe at 0°. The image on the monitor is generated from scan lines going back and forth from the green edge (right side of monitor) to the red edge (left side of monitor). In the bottom image, the schematic is made transparent and the anatomy of the heart is displayed in the orientation seen in a TG midpapillary short-axis view.

FIGURE 2.7 A: 0° imaging plane. Anteflexed position provides ME five-chamber view with portion of anterior left ventricular outflow tract in imaging plane. Retroflexed position produces ME four-chamber view. B: 60° imaging plane. When performed at the level of the aortic valve, the right ventricular inflow-outflow view is seen but when imaged at the level of the mitral valve, the ME mitral commissural view is seen. C: 135° imaging plane. When performed at the level of the mitral valve, ME long-axis view is clearly seen cutting through the aortic valve and the A2 and P2 scallops of the mitral valve.

GOALS OF THE EXAMINATION

TEE examinations, whether comprehensive or abbreviated, should display all pertinent structures in the heart. Each cardiac chamber and valve should be visualized in at least two orthogonal planes. All segments of the myocardium should also be visualized. This approach helps ensure the diagnosis of any significant abnormalities and minimizes the incorrect identification of artifacts.

Echocardiographers differ in their approach to a diagnostic TEE examination. Many prefer to start with those views that examine known pathology. Others believe the examination should first systematically examine for unknown pathology before the area of concern is evaluated. A common approach starts with TG views of the left ventricle because of the frequent abnormalities detected with these views. Each of these approaches has its advantages and disadvantages, and there is no one correct way. However, the goal of any approach must be a complete examination of all structures of the heart. The 2013 Comprehensive Guidelines define a progression for the examination defining a sequence to obtain all 28 defined views. This guideline does not specifically comment on where or when to utilize the additional techniques of color flow or spectral Doppler. It doesn’t say when tissue Doppler imaging should be employed. The guideline is set up to describe a protocol of how to obtain all images in a recommended order. Other sources such as the University of Toronto have published a similar algorithm of how to obtain the views (3).

To be clear, there is no consensus on which echocardiographic views should be captured and the order of capture. The majority of practicing echocardiographers, both cardiologists and anesthesiologists do not capture all images in every patient. The look of the examination is different in the hands of every clinical provider. That being said, each view in the comprehensive examination holds a key clinical indication and has defined required structures that will increase the diagnostic yield of the view.

The comprehensive examination sequence described here is based on progressive esophageal advancement of the probe to evaluate cardiac anatomy and function followed by progressive withdrawal for the
evaluation of the aorta. This approach minimizes manipulation of the TEE probe, thereby shortening the examination time. This author has not found the depth of probe insertion to be a reliable tool for identifying intracardiac anatomy. The preferred approach is to report the location of cardiac anatomy/pathology relative to known intracardiac structures and standard cross-sectional views. The progressive advancement/removal of the probe provides a systematic anatomic orientation (avoiding disorientation as to the displayed imaging plane) and allows for easy description of anatomy relative to other cardiac structures. Pathology in the aorta can be referred to the depth of probe insertion but this has more value in the long-term outpatient evaluation of lesions. The value in the intraoperative examination lies mainly in confirming lack of change after cardiopulmonary bypass (e.g., retained presence of mobile atheroma vs. embolization).

THE COMPREHENSIVE EXAMINATION

Midesophageal Ascending Aortic Short-Axis View

From the initial position following passage into the esophagus, the probe is advanced slightly until the proximal aorta is seen. The probe angle is then rotated until a true short-axis is seen, usually between 0° and 45°. The main pulmonary artery is seen bifurcating and the right pulmonary artery will lie posterior and perpendicular to the proximal aorta (Fig. 2.8).

This view is useful for identifying pulmonary artery catheter placement as well as for visualizing thromboembolism in the pulmonary artery.

FIGURE 2.8 Midesophageal ascending aortic short-axis view.

Midesophageal Right Pulmonary Vein View

The probe is then turned to the right to display the ME right pulmonary vein view. Small changes in depth and angle may be needed to optimize this view. The right upper pulmonary view is seen entering the left atrium from the approximate 7 o’clock position in the far field and the lower pulmonary vein is seen near field traveling left to right into the atrium. The orientation of the upper view allows for pulsed-wave spectral Doppler interrogation but the lower view is perpendicular and can rarely be interrogated with spectral Doppler. The superior vena cava is often seen in the short-axis to the right of the upper pulmonary vein (Fig. 2.9).

FIGURE 2.9 Midesophageal right pulmonary vein view. Ao, aorta; LA, left atrium; SVC, superior vena cava; RUPV, right upper pulmonary vein.

FIGURE 2.10 Midesophageal ascending aortic long-axis view.

Midesophageal Ascending Aortic Long-Axis View

The probe is then turned back to the left and the ME ascending aortic short-axis view is reacquired. From here, the probe angle is rotated to visualize the proximal aorta in the long-axis. The right pulmonary artery is seen in cross-section at the apex of the imaging sector. This view may identify the proximal extent of a dissection, may allow for visualization of saphenous vein grafts, and can also be used to interrogate the proximal suture line of an ascending aortic tube graft (Fig. 2.10).

Midesophageal Aortic Valve Short-Axis View

The imaging plane is then rotated back to 45° and then advanced to obtain the ME aortic valve short-axis view. For novice examiners or when anatomy is confusing, the ME aortic valve short-axis, can be used as a reference point to start the examination. The recognizability of the aortic leaflets makes this image easy to identify. Evaluation should include the size of the aortic valve, in comparison with the atrial chambers, the mobility of the aortic leaflets and the presence of leaflet calcification.

The primary diagnostic goals of this view are to define the general morphology of the aortic valve (e.g., bicuspid vs. tricuspid) and to determine if aortic stenosis is present. The classic “Mercedes-Benz” view of the aortic valve is seen with the noncoronary cusp in the near field of the valve on the left, the left coronary cusp on the right, and the right coronary cusp in the far field of the valve. The relative sizes of the aorta and the atria should be noted. Slight withdrawal of the probe will reveal the origins of the left and
right coronary arteries at approximately 2 and 6 o’clock respectively. If the left main coronary bifurcation is seen, the circumflex coronary artery will travel upward toward the sector apex and the left anterior descending coronary artery will travel downward toward the far field of the image. The intra-atrial septum is observed originating near the noncoronary cusp of the aortic valve and should be inspected for openings consistent with an atrial septal defect. In addition, look for continuous deviation of the septum away from an atrium with elevated pressures (Fig. 2.11). This view, along with the ME bicaval view, is used extensively in structural heart procedures involving atrial septal puncture (4).

FIGURE 2.11 Midesophageal aortic valve short-axis view. LA, left atrium; RA, right atrium; TV, tricuspid valve; RV, right ventricle; PV, pulmonic valve; N, noncoronary aortic valve cusp; L, left coronary aortic valve cusp; R, right coronary aortic valve cusp.

Midesophageal Right Ventricular Inflow-Outflow

After completion of the ME short-axis view of the aortic valve, the next three views are obtained at the level of the aortic valve in the longitudinal plane. The first view is the ME right ventricular inflow-outflow view.
Start at the ME aortic valve short-axis and, without moving the probe, change the rotation of the imaging angle to approximately 60° to 90°. The desired imaging plane will visualize the tricuspid valve, right ventricular outflow tract (RVOT), and proximal pulmonary artery. Note that the right atrium will be at 10 o’clock, the tricuspid valve at 9 o’clock, the right ventricular cavity at 6 o’clock, and the pulmonary valve and pulmonary artery at 3 o’clock. Two leaflets of the tricuspid valve are seen in this view. The leaflet on the left is the posterior leaflet and the leaflet to the right near the aortic valve is either the anterior or septal leaflet.

The primary diagnostic goals of this view are to measure the tricuspid and pulmonary annulus sizes and to evaluate the pulmonic valve. Two of the pulmonary valve leaflets are visualized with the left or right cusp seen on the left and the anterior cusp seen on the right. The RVOT diameter is best measured here for subsequent calculation of right-sided stroke volume. This view is often superior to the ME four-chamber view for spectral Doppler interrogation of the tricuspid valve. The short septal tricuspid leaflet often directs the regurgitant jet toward the atrial septum in a path parallel to the Doppler beam angle. In adults with uncorrected congenital heart disease or prior congenital heart surgery, evaluation of the RVOT and pulmonary valve may provide important diagnostic information. In addition color flow Doppler in this view can discriminate perimembranous from supracristal ventricular septal defects (See Chapter 5).

This view may be helpful in confirming the location of a pulmonary artery catheter if a diagnostic waveform is not identified. The echodense linear pulmonary artery catheter will be seen in the proximal pulmonary artery if the catheter is in the correct location (Fig. 2.12).

Midesophageal-Modified Bicaval Tricuspid Valve View

If a tricuspid regurgitant jet is not adequately interrogated, turn the probe to the right (clockwise) and the ME-modified bicaval tricuspid valve view is seen (Fig. 2.13). In this view spectral Doppler is usually effective for interrogation of noneccentric TR jets. The tricuspid leaflet seen on the left side of the image is either the posterior or septal leaflet and the one on the right is the anterior leaflet.

Midesophageal Aortic Valve Long-Axis View

The ME aortic valve long-axis view is obtained by further rotating the imaging angle to approximately 110° to 130°. A slight turn of the probe toward the patient’s right may be necessary to optimize this image. The view is complete when the left ventricular outflow tract, aortic valve, and proximal ascending aorta are displayed together. Additional structures to observe are the outflow tract itself, the sinus of Valsalva, and the sinotubular junction.

The primary diagnostic goal of this view is to evaluate aortic valve function and annular and sinotubular dimensions. The left ventricular outflow tract diameter is often measured in this view. The proximal ascending aorta should be inspected for calcification, enlargement, and protruding atheroma. The size of the proximal ascending aorta can be measured by identifying the largest anterior-posterior diameter seen. An important limitation of this view is that the aortic cannulation site in the distal ascending aorta cannot be visualized. After completion of a 2D examination, aortic valve function is evaluated further with color flow Doppler (Fig. 2.14).

Midesophageal Bicaval View

The ME bicaval view is then obtained by turning the probe further to the patient’s right. This image is often best with 5° to 15° less rotation than in the ME aortic valve long-axis view. The key structures in this view are the left and right atria, inferior and superior vena cavae, interatrial septum, and right atrial appendage. Minor adjustment to probe depth and multiplane angle will often bring the tricuspid valve or coronary sinus into view (Fig. 2.15).

The primary diagnostic goals of this view are to examine for atrial chamber enlargements and the presence of a patent foramen ovale or an atrial septal defect, and to detect intra-atrial air. If the integrity of the intra-atrial septum is questioned, color flow Doppler or bubble contrast should be performed.

This view may be helpful in the placement of pulmonary artery catheters in patients where entry into the right ventricle is difficult. The pulmonary artery catheter is floated to 20 cm and the balloon inflated and advanced. When the echodense inflated balloon enters the proximal superior vena cava it will be seen entering the right atrium. The catheter can be turned clockwise or counterclockwise to steer it toward the tricuspid valve at approximately 7 o’clock in the atrium rather than the inferior vena cava located at approximately 9 o’clock.

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