Two-Dimensional Examination



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 By gripping the probe shaft near its entrance in the mouth, the probe can be advanced or withdrawn.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 image 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.




Apr 16, 2020 | Posted by in ANESTHESIA | Comments Off on Two-Dimensional Examination
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