Wyman W. Lai1 and Jacqueline Wheatley2 1 CHOC Children’s Heart Institute, Orange, CA; University of California, Irvine School of Medicine, Irvine, CA, USA 2 The Hospital for Sick Children, Toronto, ON; Mohawk College, Hamilton, ON, Canada The basic elements of a standard transthoracic echocardiography (TTE) examination are 2D images supplemented by Doppler and color Doppler information in multiple orthogonal imaging planes [1]. The use of M‐mode echocardiography is reserved primarily for the assessment of ventricular performance [2], although some current pediatric recommendations call for 2D assessment of left ventricular size and function [3]. Any laboratory performing a pediatric echocardiogram should have a written examination protocol that outlines the views to be obtained, the imaging modalities to be deployed for each view, and the preferred methods for recording and display. Whenever possible, the initial pediatric echocardiogram should be a complete study. A list of the structures to be examined with each view is helpful, and the required versus optional measurements should be clearly defined. A complete transthoracic pediatric echocardiogram should include a quantitative assessment of left ventricular size and systolic function (see later) [4]. Pediatric TTE is organized by acoustic “windows” from which the heart is examined. Many pediatric echocardiography laboratories begin the examination with subxiphoid, or subcostal, imaging instead of left parasternal views. This allows for the determination and display of visceral situs (site and/or location) at the beginning of an examination. Regardless of where the examination starts, the segmental approach is used to describe all of the major cardiovascular structures in sequence [5–7]. Complete sweeps of the heart should be made during the examination to rule out abnormalities at its base or apex or on one of its surfaces. The study information should be recorded as a combination of complete sweeps and multiple selected single‐plane images [8–10]. Most ultrasound systems are configured so that a notch, or some other marking, on the side of a transducer corresponds to the side of a symbol displayed at the top of the image sector, usually to the right side of the screen (from the viewer’s perspective). Therefore, when the transducer is positioned with the notch to the patient’s left (at the 3 o’clock position), the left side of the patient will be displayed on the right of the screen. When the transducer is counterclockwise rotated so that the notch is directed superiorly (at 12 o’clock), the superior structures are displayed on the right of the screen. In the course of a routine sweep, the transducer notch position is held in a fixed position, and the transducer is angled to obtain a series of images in the desired imaging plane. Because of the wide range of complex pathology that may be seen on a pediatric echocardiogram, images should be shown in their correct spatial, or “anatomically correct,” position on the display screen. Therefore, the anterior and superior structures are displayed at the top of the screen, and the rightward structures are generally placed on the left side of the image display (with the exception being the parasternal long‐axis view where the cardiac apex is displayed by convention on the left of the screen). The diagnostic accuracy of an examination depends greatly on the image quality. Technical adjustments should be made throughout the examination by the operator to improve signal‐to‐noise ratio and image resolution. The appropriate probe and optimal transducer frequency are selected to image the structures in question, and adjustments of the electronic (acoustic) focus depth are made throughout the study as necessary. Centering of structures of interest, using an appropriate degree of magnification, and optimizing of windows for imaging and Doppler interrogation are critical for image quality. The optimal window should allow the ultrasound beam to be directed perpendicularly to structures of interest for 2D imaging. The ultrasound beam should be parallel to flow for Doppler interrogation and color flow mapping. The appropriate color box size should be used in order to maintain an adequate frame rate (the smaller the color box, the higher the frame rate), and selecting the proper color velocity range for the region of interest is crucial for accurate assessment. Patient position, comfort, and level of anxiety are important considerations during the examination. In the usual performance of an echocardiogram, the goals from each view should be: (i) imaging of cardiovascular structures; (ii) color and/or spectral Doppler interrogation of each valve and other major cardiovascular structures; and (iii) a complete evaluation of any suspicious chamber, vessel, or flow jet identified during the course of the examination. Tables 4.1–4.5 list the structures that should be visualized from the standard examination views. During the progress of pediatric TTE, the sonographer or echocardiographer must keep in mind the indications for the study and the need to address potential issues that may affect treatment. A complete examination may require that custom, or “in between,” planes be used to investigate or display an abnormality. Table 4.1 Structures viewed from subxiphoid (subcostal) sweep/views Table 4.2 Structures viewed from apical sweep/views Extracardiac structures are also visualized during a standard TTE examination. Mediastinal abnormalities such as masses or cysts, if present, should be noted [11,12]. The presence or absence of the thymus may be seen in young children. Careful attention to symmetry and amplitude of diaphragm motion and screening for pleural effusions from subxiphoid and flank windows is particularly important in postoperative cardiac patients. Table 4.3 Structures viewed from left parasternal sweep/views Table 4.4 Structures viewed from suprasternal notch sweep/views Table 4.5 Structures viewed from right parasternal views The five standard views of a pediatric TTE, as defined by the American Society of Echocardiography, are all employed as part of a routine examination including subxiphoid (subcostal), apical, parasternal (left parasternal), suprasternal notch, and right parasternal (Tables 4.1–4.5) [13]. These imaging planes provide unique information regarding cardiovascular malformations that are often seen in childhood. A complete examination requires that the cardiovascular structures be imaged from multiple orthogonal planes. This practice minimizes artifacts due to false “dropout” of structures imaged parallel to the beam of interrogation, “shadowing” from reflective structures proximal to the area of interest, or “mirroring” from the reflection of ultrasound on tissue layers. The imaging planes are identified by transducer location (subxiphoid, apical, left parasternal, suprasternal notch, and right parasternal) and by the plane of examination relative to the heart (four chamber, two chamber, long axis, and short axis) (Figure 4.1). In addition, imaging planes may be described as anatomic planes (sagittal, transverse/axial, or coronal). The views and structures presented in the following sections are described as seen in a patient with normal or near‐normal cardiovascular anatomy. This imaging plane provides a great deal of information, particularly in young children who tend to have good acoustic windows. The child is placed in the supine position. For larger children, placing a pillow under their bent knees may help to relax the abdominal muscles. Subxiphoid imaging [14–16] begins with the determination of abdominal visceral situs in the transverse plane. The transducer is positioned with the notch at the 3 o’clock position as viewed from inferiorly with anterior structures displayed at the top of the screen. In addition to visualization of the liver and stomach, the spleen should be sought in patients with suspected abnormal abdominal visceral situs (e.g., heterotaxy syndrome). The location of the hepatic segment of the inferior vena cava and descending aorta in relation to the midline and one another are determined from this view (Figure 4.2, Video 4.1). The patency, size, and collapsibility of the inferior vena cava should be documented in its long axis (the transducer is rotated counterclockwise so that the notch is at the 12 o’clock position), and the abdominal descending aorta should also be demonstrated (Figure 4.3, Videos 4.2 and 4.3). If a dilated azygos vein is seen posterior to the descending aorta, interruption of the inferior vena cava should be suspected. Inadvertent compression of the inferior vena cava, mimicking interruption, may be avoided by reducing the amount of abdominal pressure used to obtain the image. Figure 4.1 Line drawing of transducer locations for standard imaging windows. Figure 4.2 Axial view in color compare mode demonstrating 2D and color Doppler images of a child with normal abdominal visceral situs. Ao, aorta; IVC, inferior vena cava. With the notch again at 3 o’clock, the plane of imaging is angled from the abdomen to the thorax to obtain the “situs sweep” (Videos 4.4 and 4.5). The connections of the hepatic veins to the inferior vena cava are visualized, followed by the connection of the inferior vena cava to the right atrium. The position of the heart in the left thorax may also be determined in this sweep. The descending aorta at the level of the diaphragm should be identified, and any additional vascular structures crossing the diaphragm should be fully investigated by 2D imaging and color flow mapping. It is useful to visualize both hemidiaphragms at the same time in the subxiphoid long‐axis (transverse) view to document normal diaphragmatic motion with respiration. The image is then inverted so that the superior structures are displayed at the top of the screen. The subxiphoid long‐axis (coronal, frontal) sweep begins in the transverse plane and utilizes the liver as an acoustic window to the heart (Figure 4.4, Video 4.6). The connections of the hepatic veins to the inferior vena cava should be documented, as well as the entrance of the inferior vena cava to the right atrium. As the sweep passes the inferior/posterior surface of the heart, the coronary sinus is often well visualized along the left posterior atrioventricular groove, and the posterior descending coronary artery may be seen in the posterior interventricular groove. The long‐axis view allows for good visualization of the atrial septum and characterization of right versus left atrial and ventricular morphology. As imaging transitions into a nearly coronal plane, the ventricular outflow tracts are well displayed, as is the right atrial appendage and the proximal portion of the normal right superior vena cava to the right of the ascending aorta. The position of the left coronary artery ostium may be visualized as the sinuses of Valsalva and ascending aorta are imaged. The bifurcation of the main pulmonary artery into the branch pulmonary arteries should be documented during the sweep. Color flow mapping in the subxiphoid long axis may be advantageous for interrogation of the atrial septum and the anterior muscular septum (Video 4.7). To visualize the true long axis of the atrial septum, the transducer should be rotated in between the subxiphoid long‐ and short‐axis views (left anterior oblique plane, see later). Sweeping from this plane can further elucidate defects in the inferior atrial septum that might be underappreciated in the standard subxiphoid views. The subxiphoid short‐axis (sagittal) sweep (Figure 4.5, Videos 4.8 and 4.9) starts in a sagittal plane with the transducer notch positioned inferiorly (6 o’clock). The short‐axis “reference view” includes the atria (including the right atrial appendage), the atrial septum, and the superior and inferior venae cavae. The Eustachian valve – the venous valve of the inferior vena cava – is frequently seen in this view as an extension of the anterior wall of the inferior vena cava and should not be confused with the atrial septum [17]. The imaging sweep normally begins to the right of the patient, allowing visualization of the right upper pulmonary vein as it passes lateral and posterior to the superior vena cava and then proceeds from the base to the apex of the heart. The right pulmonary artery is seen in cross‐section posterior to the superior vena cava and above the roof of the left atrium. The arch of the azygos vein above the right pulmonary artery and into the superior vena cava may also be visualized in this sweep. Atrial septal morphology, including the apposition of the septum primum and septum secundum, is often well seen in the short‐axis plane. The tricuspid valve is imaged before the mitral valve as the transducer passes from right to left. The morphology of the atrioventricular valves, including fibrous continuity between the atrioventricular and aortic valves, can be identified as the imaging plane passes the atrioventricular canal region. The transducer position may need to be repositioned during the sweep (generally more rightward on the abdomen, taking advantage of the right‐sided liver as an acoustic window) to maintain a short‐axis imaging plane as the apex of the heart is visualized. A list of structures that should be identified on the subxiphoid views is provided in Table 4.1. Color flow mapping of the atrial and ventricular septa, particularly in smaller children, is often best visualized in the subxiphoid short‐axis sweep. It is important to lower the color flow Doppler scale due to the poor angle of interrogation for flow across portions of the ventricular septum and to capture low‐velocity shunts. Doppler interrogation of the descending aorta at the level of the diaphragm, the hepatic vein, and the superior vena cava is recommended as part of a complete examination in all patients. Figure 4.3 Long‐axis composite image of uninterrupted inferior vena cava and descending aorta. (a) IVC, inferior vena cava; HV, hepatic vein; RA, right atrium. (b) Abd. Ao, abdominal aorta; Ao. arch, aortic arch. Figure 4.4 Line drawing and serial images of subxiphoid long‐axis (coronal, frontal) sweep. (1) DAo, descending aorta; LA, left atrium; LV, left ventricle; MV, mitral valve; RA, right atrium. (2) Ao arch, aortic arch; AoV, aortic valve; LPA, left pulmonary artery; RPA, right pulmonary artery; TV, tricuspid valve. (3) Ao, aorta; LCA, left coronary artery; MPA, main pulmonary artery; RSVC, right superior vena cava. (4) LV, left ventricle; PV, pulmonary valve; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract; TV, tricuspid valve. Standard apical four‐chamber and long‐axis (“three‐chamber”) – as well as, in many laboratories, apical two‐chamber – views are obtained [18]. The child is placed in a partial left lateral decubitus position with the left arm raised to bring the apex of the heart closer to the chest wall, and the apical impulse may be palpated for transducer placement. The notch of the transducer is directed toward the left axilla, at the 2–3 o’clock position as viewed from the apex. The four‐chamber sweep (Figure 4.6, Video 4.10) begins posteriorly to demonstrate the length of the coronary sinus [19], the entrance of the inferior vena cava into the right atrium bordered anteriorly/inferiorly by the Eustachian valve, and the thoracic descending aorta posterior to the left atrium in the nearly transverse plane. The sweep covers the anterior surface of the heart after passing through the atrioventricular valves and the left ventricular outflow tract (Table 4.2). Careful color flow mapping of the ventricular septum can help to discern any ventricular septal defects, particularly in the apical muscular septum (Video 4.11). Importantly, this view should not be used to interrogate the atrial septum as it is parallel to the ultrasound beam and false dropout can occur. Figure 4.5 Line drawing and serial images of subxiphoid short‐axis (sagittal) sweep. (1) IVC, inferior vena cava; LA, left atrium; RA, right atrium; RPA, right pulmonary artery; RUPV, right upper pulmonary vein. (2) EV, Eustachian valve; RPA, right pulmonary artery; RSVC, right superior vena cava; Sept. 1°, septum primum; Sept. 2°, septum secundum; *, region of the right atrial appendage. (3) Ao, aorta; MPA, main pulmonary artery; MV, mitral valve; PV, pulmonary valve; TV, tricuspid valve; VS, ventricular septum. (4) ALPM, anterolateral papillary muscle; PMPM, posteromedial papillary muscle. The apical four‐chamber reference view allows for spectral and color Doppler interrogation of the atrioventricular valves and the characterization of ventricular morphology (Video 4.12). With the proper adjustments, the apical displacement of the normal tricuspid annulus relative to the mitral annulus, ventricular trabeculations, and the moderator band may be well visualized. Angling anteriorly from the standard four‐chamber view, the “five‐chamber” view highlights the left ventricular outflow tract and ascending aorta (Figure 4.6(1)). Repositioning of the transducer medially toward the lower left sternal border and moving up one or two rib spaces brings the right ventricular inflow and right ventricular free wall more into alignment with the beam of interrogation (Video 4.13). Superior and anterior angulation from this position brings the right ventricular outflow tract into alignment and often offers an optimum angle for Doppler interrogation of the right ventricular outflow tract and color flow mapping of the pulmonary valve (Figure 4.7, Video 4.14). The apical long‐axis (“three‐chamber”) view is obtained by rotation of the transducer clockwise approximately 60° from the four‐chamber view (Figure 4.8, Video 4.15), with the transducer notch at 4 o’clock. Some laboratories image the “three‐chamber” view by rotating the transducer counterclockwise from the four‐chamber view to place the transducer notch at approximately 10 o’clock (Video 4.16). Imaging of the left ventricular outflow tract from the apex allows for visualization of subaortic structures oriented perpendicular to the plane of insonation [20]. The long‐axis view allows for optimal Doppler interrogation of the left ventricular outflow tract and ascending aorta as well as color flow mapping of the aortic valve. Modified views foreshortening the left ventricle may allow clearer visualization of the left ventricular outflow tract.
CHAPTER 4
The Normal Pediatric Echocardiogram
Examination principles
Inferior vena cava
Hepatic veins
Abdominal aorta
Diaphragm
Superior vena cava
Left atrium
Right atrium
Atrial septum
Coronary sinus
Pulmonary veins
Mitral valve
Tricuspid valve
Left ventricle
Right ventricle
Ventricular septum
Left ventricular papillary muscles
Left ventricular outflow tract
Aortic valve
Right ventricular outflow tract
Pulmonary valve
Ascending aorta
Coronary arteries
Main and branch pulmonary arteries
Pericardium
Inferior vena cava
Left atrium
Right atrium
Atrial septum
Coronary sinus
Selected pulmonary veins
Mitral valve
Tricuspid valve
Left ventricle
Right ventricle
Ventricular septum
Left ventricular papillary muscles
Left ventricular outflow tract
Aortic valve
Right ventricular outflow tract
Pulmonary valve
Ascending aorta
Main and branch pulmonary arteries
Inferior vena cava
Superior vena cava
Left atrium
Right atrium
Atrial septum
Coronary sinus
Pulmonary veins
Mitral valve
Tricuspid valve
Left ventricle
Right ventricle
Ventricular septum
Left ventricular papillary muscles
Left ventricular outflow tract
Aortic valve
Right ventricular outflow tract
Pulmonary valve
Ascending aorta
Coronary arteries
Main and branch pulmonary arteries
Pericardium
Superior vena cava
Left atrium
Pulmonary veins
Ascending aorta
Superior thoracic aorta
Main and branch pulmonary arteries
Aortic arch
Proximal brachiocephalic arteries
Left innominate vein
Inferior vena cava
Superior vena cava
Right atrium
Atrial septum
Right pulmonary veins
Ascending aorta
Right pulmonary artery
Standard orthogonal imaging views
Subxiphoid (subcostal) views
Apical views
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