An echocardiographic examination can and should be much more than a simple definition of cardiac anatomy. A thorough evaluation not only defines cardiovascular anatomy but also describes myocardial performance, valvar function, and overall hemodynamics. Therefore, our approach to the echocardiographic examination must allow complete and efficient definition of all of these factors, while also taking into account patient comfort, age, and clinical situation. In this chapter, we will review some of the practical issues surrounding the performance of congenital and pediatric echocardiography. These issues involve everything from patient cooperation to complex hemodynamic analyses and digital image archiving. In this chapter, we hope to provide readers with a solid foundation on which to build their understanding of echocardiography and its use. We will review a general approach to the examination, image acquisition, archiving, and report generation. A standardized method of image orientation and an outline of the segmental analysis of cardiovascular anatomy will also be presented.
GENERAL EXAMINATION GUIDELINES
The examination process should begin even before the examiner meets the patient. The first step is to understand the events that led to a referral for the study. This can be accomplished by reviewing the patient’s history and/or interviewing the patient and/or family before acquiring any images. Particular attention should be paid to prior cardiovascular events, symptoms, and/or treatments (if any). Review of the written operative notes is crucial for the patient with a history of surgical intervention. Precise knowledge of the details of the preceding “repairs” allows the echocardiographer to perform a more thorough and efficient study. It is also prudent to confirm the details of what is learned from written records by discussing the history with the patient and/or accompanying family members before beginning the examination. When no information is available, inspection of the patient’s color, respiratory status, and chest can be helpful. A cyanotic or distressed infant is more likely to have complex malformations than is the school-age child presenting for evaluation of a murmur. If sternotomy or lateral thoracotomy scars are present, they confirm previous surgical interventions, even though they do not define the specific procedure. In the remainder of this chapter, we will focus primarily on the approach to a comprehensive echocardiographic study. However, there are times when a more goal-directed approach is prudent or even required. These limited examinations are appropriate when the primary anomaly has been well defined and/or the patient is presenting for a “recheck” of a residual abnormality, such as a pericardial effusion. The advent of digital imaging, archiving, and reporting systems has simplified the process necessary to obtain historical information and compare current findings with the patient’s prior status. There are many commercially available systems that provide all of these features. During an echocardiographic examination, it is important to have access to not only the electronic medical record but also any previous imaging studies. Ideally, the electronic reporting and archiving tool used will not only display current and past images but also allow for creation of the clinical echocardiographic report within the same program. Any previous reports should be reviewed before beginning an examination. The quantitative measurements obtained should be compared to historical baselines before the conclusion of the study. The ability to quickly perform side-by-side comparison of current images with previous examinations has been a major advance associated with digital echocardiography, allowing for easier and more accurate assessment of changes in cardiac findings over time.
The second phase of the examination also occurs before scanning begins. This is when the examiner assesses the patient’s clinical status. This information should be documented in the patient’s clinical report and should include definition of the patient’s heart rate and rhythm, blood pressure, and state of consciousness during the examination. This information is required because hemodynamic data obtained from a sedated patient need to be interpreted differently from those obtained from the agitated or awake “but calm” patient. When the state of consciousness is anything other than awake and calm, this should be documented within the formal report. Additional pieces of information that should be included in the report relate to the patient’s body size. Height, weight, body mass index, and body surface area should all be documented on the report and linked to the measurements obtained. These biometric values become especially important when determining whether specific chamber sizes or wall thicknesses are normal or abnormal relative to the general population.
When measuring blood pressure, it is important to use cuffs of appropriate size. The width of the inflatable bladder should cover most of the upper arm between the elbow and shoulder. Smaller cuffs will result in artificially elevated readings. It is advisable to use the right arm for these determinations, because the right arm will be upstream from a coarctation in the majority of patients. Occasionally, the patient’s state changes between the initial measurement and the time that important Doppler measurements are made. In these cases, a repeat blood pressure measurement should be obtained. For example, if the patient is initially agitated or anxious but becomes more relaxed during the examination, repeating the blood pressure measurement will give a more accurate picture of the patient’s hemodynamic state at the time of the Doppler measurements.
Finally, the scan can begin. The ultrasound system and examination room in a pediatric/congenital cardiac ultrasound laboratory must have features that would not normally be found in a laboratory solely devoted to the care of adults with acquired cardiac disorders. The echocardiographic system must have a wide range of transducers to allow for the variation in body habitus and image quality associated with congenital heart disease. In a single day, the system may be used to study neonates, fetuses, and adults with histories of multiple complex surgical repairs (and the challenging acoustic windows that accompany that history). Three or four phased-array transducers, with frequencies ranging from 3 to 12 MHz, represent a minimal complement for a congenital echocardiographic system. A 2-MHz nonimaging continuous-wave Doppler transducer is often needed to clearly define weak Doppler signals. Linear and curvilinear probes, in addition to phased-array transducers, are helpful for vascular and fetal studies, respectively.
The waiting and examination rooms should be nonthreatening, comfortable, and spacious (Fig. 2.1). Several family members often accompany patients with congenital heart defects to their appointments. It is best to include the family in the examination, avoiding issues of separation anxiety in both the children and their parents. The examination room and table should be kept at a comfortable temperature, remembering that the patient will be partially undressed for the study. Providing entertainment/distractions, both in the waiting room and during the examination, is extremely helpful in achieving a complete examination of complex cardiac malformations. Television monitors or digital video players can be strategically positioned so that the patient can be watching a movie of his or her choice while the echocardiographic data are being obtained. We have found that patient cooperation and comfort are enhanced by having the person who is to perform the initial examination meet the patient/family in the waiting area, assist them with choosing music or a video to play during the test, and then escort them to the examination room.
In the very young patient (about 2 months to 2 years of age) or for more invasive procedures (such as transesophageal echocardiography), even these measures may not be enough to relieve the patient’s anxiety. In these situations, it is appropriate to consider the use of conscious sedation or even monitored anesthesia care. Complete guidelines for use of conscious sedation have been provided by the American Academy of Pediatrics. The method of sedation should be chosen such that both patient safety and the quality of the examination are maximized. Common sense suggests and the Academy guidelines require that, regardless of the agent(s) used, a practitioner who is not involved in the procedure be present and responsible for monitoring the patient’s well-being and vital signs while sedated. Pulse oximetry, in addition to heart rate, rhythm, and blood pressure, is also a mandatory component of monitoring when using sedative agents. Additional information regarding equipment and training necessary for conscious sedation can be found in the American Academy of Pediatrics guideline document (see Suggested Reading).
Figure 2.1. A congenital echocardiographic laboratory can accommodate the needs of a wide variety of patients. Top: A waiting area with space for families and activities for all ages. Bottom: One way of arranging an echocardiographic examination room to meet both the medical needs of the patient and the needs of the patient’s family members. Examination rooms in the congenital suite must be somewhat larger than those found in a standard adult laboratory. Comfortable seating for accompanying family members, a child-friendly environment, and videos for distraction during the examination make an otherwise intimidating process less threatening. The ultimate purpose, of course, is to improve the information obtained during the echocardiographic examination.
Transesophageal echocardiography in pediatric patients will often require deep sedation or general anesthesia. Some teenage patients may be mature enough to allow a transesophageal examination using standard conscious sedation. The choice of sedation protocol must be tailored to the patient, the reason for the examination, and the availability of appropriate personnel and anesthesia equipment. A complete discussion of the training required for and the practical aspects of performing transesophageal echocardiography can be found later in this book and in The Echo Manual.2
Echocardiographic examinations have become indispensable in several hospital settings. Intraoperative echocardiography is now an integral part of surgical care. Intensive care unit patients often benefit from hemodynamic evaluations provided by a detailed echocardiogram. However, these environments are not the quiet controlled spaces that we are accustomed to in the echocardiographic laboratory. Once the examiner is at the bedside or in the operating room, he or she must be certain to not interfere with the other cares being provided. Hand and probe hygiene must be meticulous, and use of sterile, ultrasound transparent, barriers should be considered in the postsurgical suite, when scans near surgical wounds are required. One advantage of the bedside examination is that the continuous hemodynamic monitoring available often makes hemodynamic conclusions even more accurate. Certainly, measured central venous or arterial pressures are superior to an assumed atrial pressure or a cuff-determined blood pressure. In most cases, the challenges associated with inpatient, bedside examinations are easily overcome with patience and communication with the bedside staff.
Image acquisition should be gated and synchronized with the electrocardiogram. When cardiac rhythms are irregular or when performing fetal examinations, digital clips of specified times can be used. The length of the digital clip should be determined by the patient’s heart rate and the information being recorded. For standard images, we prefer a clip that includes three cardiac cycles. Although a three-cycle clip requires more storage space than a single beat, the longer clip usually results in more satisfactory playback and less “stitch artifact” as the recording loops from the final to the initial frame. When acquiring sweeps (to display spatial relationships of one structure to another), a longer acquisition is more effective (6 to 10 beats, or 5). These longer clips are especially helpful when searching for intricately subtle defects or demonstrating the relationships of the supracardiac great vessels.
In general, the examination of children and patients with congenital heart disease follows a relatively set pattern. All patients must have a determination of blood pressure at least once during the examination. In uncooperative patients, this may occur after the images are acquired to avoid further aggravating the child. A continuous, single-lead electrocardiogram is recorded and displayed simultaneously with the ultrasound image. The electrocardiogram is a mandatory part of the complete examination; without it, accurate timing of the cardiac events visualized is not possible.
At each transducer position, the examination should initially focus on a clear demonstration of the two-dimensional anatomy. Images should be recorded in the classic planes (see image orientation section later in this chapter). However, the examination is not complete unless the scans include all of the areas visible from each transducer position, even those that do not conform to standard imaging planes. For example, when scanning in a sagittal plane, one must sweep the beam as far to the right and left as the acoustic window will allow. Once the examiner is familiar with the structures seen from that transducer position, more focused anatomic scans of abnormal areas, color and spectral Doppler recordings, and three- dimensional acquisitions can be performed. At the conclusion of the echocardiographer’s examination, the images should be reviewed, ideally by both the echocardiographer and the reviewing physician, to ensure completeness. If immediate physician review is not possible, the images should still be reviewed by the examiner to ensure that the recording accurately displays all of the information that was acquired. When this initial review reveals missing or poorly displayed information, additional images can be obtained while the patient is still in the laboratory.
The order in which images are recorded should be standardized, but the precise sequence is determined by local preferences and patient behavior. When dealing with a cooperative patient, we prefer to begin with the subcostal position. In neonates and young infants, this window will often provide visualization of nearly the entire cardiovascular system. More anterior and superior structures can be difficult to assess from the subcostal window in older patients. In these cases, images from the subcostal position will focus primarily on the inferior and superior venae cavae, the atrial septum, and the ventricular chambers themselves. An effort to visualize the pulmonary venous connections should also be made from this position. This will be more successful in younger patients, but a surprising number of mature patients can be extensively evaluated from this transducer position.
Once all of the information available from the subcostal window has been obtained, our attention usually shifts to the anterior chest wall. Initial scans are oriented in the sagittal (long-axis) plane. The initial focus is on the left ventricular inflow and outflow tracts, noting the size and position of each chamber and the valves and their relationships to one another. The plane of sound is then oriented toward the right ventricular inflow tract, demonstrating the inferior vena cava–right atrial junction, right atrium and its appendage, and the tricuspid valve. The right ventricular inflow view often allows an advantageous alignment with tricuspid regurgitant flow.
Parasternal sagittal scanning is followed by horizontal sweeps (short-axis scans) in the same area. Doppler evaluation of the right ventricular outflow tract and pulmonary arteries is often optimal from these positions. Images obtained from this window have been used to define many of our normal quantitative values related to atrial and annular dimensions, as well as left ventricular cavity diameters and wall thickness. Coronary arterial anomalies are best detected using horizontal plane scans near the base of the heart. Definition of the ventricular septum and exclusion of ventricular septal defects (VSDs) require focused color flow Doppler examinations in this area. These can be recorded as sweeps, or as a sequence of adjacent clips, flowing from the cardiac base to its apex or vice versa. The relationships of the great arteries (particularly the pulmonary vessels and the aorta) are best displayed in high parasternal short-axis image sweeps.
The right parasternal border should also be interrogated in a similar fashion. If the patient lies on his or her right side, images from this window are often improved. The superior and inferior venae cavae, right atrium, atrial septum, and pulmonary veins can be visualized in many patients from this transducer position. Image quality at the right parasternal border is more variable between patients than the other standard transducer positions. However, when the right heart is enlarged, this area often provides images of surprisingly high quality.
Our attention then shifts to the cardiac apex. Coronal images (four-chamber views) are usually obtained first. Size, position, and relationships of the atria, atrioventricular (AV) valves, and ventricles are documented. Volumetric assessments, whether derived from two- or three-dimensional scans, of ventricles are performed. Many spectral Doppler recordings are made from the apical window because beam alignment is optimal for the right and left ventricular inflow tracts, the pulmonary veins, and the left ventricular outflow tract. Sagittal plane images (apical long-axis and two-chamber views) are the next to receive attention. These scans provide anatomic and Doppler data related to the left ventricular inflow and outflow tracts.
Finally, the transducer is positioned at or near the suprasternal notch. This position is often saved until the end of the examination, because most children are somewhat threatened by the slight pressure on their necks required to image here. Taking a moment to prepare the child, by describing what is about to happen, is time well spent in most cases. Images from the suprasternal notch usually begin with a sagittal orientation. However, combinations of sagittal and coronal plane scans are required to clearly define the right–left relationships of the great vessels. The aortic arch, its arterial branching pattern, and sidedness should be determined. Superior systemic veins, pulmonary arteries, left atrium, and pulmonary venous structures can also be seen, even in most adults, from these positions. Doppler interrogation of the descending aorta is often optimal from this position. However, two-dimensional determinations of descending aortic diameters should not be performed from the suprasternal notch. From the notch, the plane of sound is parallel with the aortic walls. We prefer high-left parasternal images (the ductal/coarctation view; Fig. 2.2) for determination of upper descending aortic size.
Figure 2.2. The ductal/coarctation view. These two echocardiographic images were obtained from an oblique high-left parasternal transducer position. The plane of sound was moved toward the patient’s left shoulder and was rotated clockwise from the parasternal long-axis view to visualize these structures. Left: The distal main pulmonary artery (PA), ductus (arrow), and upper descending aorta (Ao). Right: Same area but in a patient with coarctation of the aorta (arrow). This view is not only an excellent position for interrogation of ductal flows but also the best plane for evaluating the size of the upper descending aorta. The luminal narrowing associated with coarctation is clearly defined because the plane of sound is perpendicular to the vessel walls in this position (right). This view should also be used to define the size of the upper descending aorta in patients with connective tissue disorders, such as Marfan syndrome. A, anterior; LA, left atrium; RA, right atrium; S, superior.
Although these standard acoustic windows are used in all patients, there are many other possible transducer positions that provide views of the cardiovascular system.
Oblique or hybrid transducer positions can often be found if one searches for them. These windows can be particularly helpful in postoperative patients, whose acoustic characteristics are often altered by their surgical procedures.
The examination sequence just described applies to comprehensive transthoracic echocardiography. A transesophageal examination should also follow an organized pattern. In the operating room with an anesthetized patient, it is often helpful to begin the examination from the transgastric transducer position. Coronal plane images allow definition of right- and left-sided structures and provide spatial orientation for the rest of the examination. The transducer can then be slowly withdrawn to the distal, mid-, and proximal esophageal positions to complete the examination. Two- and three-dimensional scans, color Doppler interrogation, and spectral Doppler flow maps should be obtained at all levels. When a patient is not anesthetized but is sedated and responsive, the examination must be modified. After esophageal intubation, it is often advisable to begin the examination at the distal esophagus. While imaging in this position, the cardiologist can also assess the level and adequacy of sedation before advancing the probe into the stomach.
The echocardiographic examination of the fetus has many unique characteristics. One is that an organized sequence of imaging is often impossible. Due to fetal motion, the examiner should obtain the most advantageous images available at the time. All of the same information should be obtained during fetal examinations. However, the order in which the tasks are accomplished cannot be standardized.
THE ECHOCARDIOGRAPHIC REPORT
The echocardiographic report requires careful construction. The reports must convey all of the pertinent information to the referring physician in an efficient, yet understandable manner. It is usually preferable to organize a report into sections. These sections would include (a) patient demographics, biometrics, and vital signs, (b) a section summarizing the most important positive and pertinent negative diagnoses/findings, (c) a section describing all of the normal or noncontributory findings documented by the examination, (d) a section detailing the quantitative measurements made during the imaging and Doppler components of the examination, and (e) a section that directly compares current with historical quantitative data pertinent to the patient’s primary diagnosis. We refer to this last section as the “serial summary.” Not all measurements are included in this area. For example, a serial summary related to aortic valvar stenosis would include a table summarizing historical values for and trends in aortic annulus diameter, left ventricular size, wall thickness, Doppler velocities and gradients, cardiac index, and valve areas.
As mentioned earlier, the report should be directly linked to the digital echocardiographic images, so that the surgeon and/or referring physician can simultaneously review both the report and the images that generated it.
IMAGE ORIENTATION AND NOMENCLATURE IN CONGENITAL HEART DISEASE
A standardized method of assessment is necessary if one is to obtain a complete understanding of even the most straightforward congenital cardiac malformations. In the setting of very complicated cardiovascular anomalies, it becomes essential. The first step in this evaluation is to consistently present echocardiographic images of the anomaly in a straightforward and reproducible way. The American Society of Echocardiography’s Pediatric Council has defined a method for “preferred” image orientation in studies involving congenital heart disease.1
We will base the remainder of this chapter on these tomographic imaging conventions. These guidelines result in echocardiographic images that are displayed in an anatomic format. Sagittal plane images are displayed with superior structures to the viewer’s right and anterior structures at the top of the video screen (Fig. 2.3). Thus, we view these images as if we were looking through the heart from the left side toward the right of a supine patient (Fig. 2.4). Horizontal plane images are displayed with anterior structures at the top of the video screen and left-sided structures to the viewer’s right (Fig. 2.5). These views simulate examining the heart of the supine patient from below, looking toward the head (see Fig. 2.4). Coronal plane images, such as the apical four-chamber view (Fig. 2.6), and the suprasternal view of the pulmonary venous confluence (“crab view,” Fig. 2.7) are displayed with superior structures at the top of the video screen and left-sided structures to the viewer’s right. These views simulate looking through the front of the heart toward the patient’s back (see Fig. 2.4). The common theme among all of these orientations is that the anatomy is displayed in a classic anatomic format, as if the patient were in front of and facing the examiner in either an upright or a supine position.
The figures and text that follow will familiarize the reader with this approach. We believe that it is best to use this system of image orientation regardless of the method used to create the image. In other words, the same anatomic features should be displayed in the same orientation whether the images are a part of a transthoracic, transesophageal, or intracardiac ultrasound examination (see Figs. 2.3, 2.5, and 2.6). Occasionally, complete consistency is not possible. This is due to the fact that most two-dimensional image displays can only be “flipped” top to bottom and/or left to right. The best examples of situations requiring more than one orientation are the sagittal views. Parasternal sagittal images follow the convention and display superior structures to the examiner’s right and anterior anatomy at the top of the video screen. Subcostal, right parasternal, and suprasternal sagittal images cannot be shown as if the patient were supine. Therefore, we opt to display the image as if the patient were standing, similar to the coronal image convention, with superior structures at the top and anterior to the viewer’s left. For many images, like the four-chamber (see Fig. 2.6) and the aortic arch (Fig. 2.8), this creates no inconsistency, because these images are not available in the parasternal window. However, the subcostal, suprasternal notch, right parasternal, and esophageal transducer positions all provide images of the venae cavae, atria, and atrial septum, the “bicaval” views (Fig. 2.9). These are parasagittal images and, according to the convention, they should be displayed with superior structures to the examiner’s right and anterior anatomy at the top of the video screen. Esophageal bicaval views conform to this convention (see bottom, Fig. 2.9). However, the angle of the interrogating plane of sound from the right parasternal, subcostal, and suprasternal positions is such that the image becomes tilted (see top, Fig. 2.9). The subcostal images are often displayed with superior structures “closest” to the top of the screen (see top left, Fig. 2.9). Mid-right parasternal images are shown with the anterior surface toward the top of the screen. The display of high-right parasternal (see top right, Fig. 2.9) and suprasternal images requires a hybrid approach, with the apex of the sector representing a transition point from anterior to superior orientations.
Figure 2.3. Standard image orientations used when scanning in sagittal planes. The left ventricular long-axis images (top left and bottom) are shown as if the patient were supine. Images obtained from the cardiac apex (middle left), suprasternal notch (middle right), or high parasternal (top right) positions are oriented as if the patient were standing. These choices are made based on the fact that the two-dimensional image cannot be rotated. Therefore, the orientation that most closely approximates one of the standardized views described in Figure 2.4is used. The paired images (right parasternal/suprasternal and left parasternal/transesophageal) demonstrate the fact that practitioners strive to display anatomy in a consistent manner, even when the image is obtained from a different acoustic window. This consistency helps avoid confusion when dealing with complex spatial relationships and anomalies of cardiac position and simplifies the use of echocardiographic data by nonechocardiographic medical providers.
Figure 2.4. Convention used to orient echocardiographic images. This is the same convention applied in all forms of tomographic imaging. The examiner in the diagram is observing the patient/echocardiographic images as if the patient were either lying in a supine position (positions 1 and 3) or standing in front of the examiner (position 2). Position 1 corresponds to images taken in sagittal planes. The examiner is looking at the patient/image from the patient’s left side. Because the patient is supine, anterior structures will be “up,” and superior structures will be to the observer’s right. Position 2 corresponds to coronal images. Here, the images are displayed as if the patient were standing upright, facing the examiner. Therefore, superior structures will now be “up,” and left-sided structures will be seen to the observer’s right. Position 3 represents horizontal plane scanning. Again, the images are displayed as if the patient were supine, but now the examiner is looking at the heart from below, as if standing at the foot of the bed. This results in an image orientation with anterior structures at the top of the video screen, while left-sided structures are again shown to the examiner’s right.
Figure 2.5. Short-axis images of the right and left ventricles and the central diagram illustrate a consistent approach to image orientation in the horizontal plane. The three echocardiographic images shown here were obtained in very different ways. The transducer was placed on the anterior chest wall near the left border of the sternum to obtain the first image (top right). In contrast, the transducer was placed on the upper abdomen, below the xiphoid, to obtain the subcostal image (bottom left). The transesophageal echocardiographic probe was advanced into the stomach and the plane of sound was angled back across the diaphragm to produce the transgastric image (bottom right). Despite the variety of maneuvers and transducer positions, the images produced can easily be seen to demonstrate the same anatomic structures. LV, left ventricle; RV, right ventricle; TEE, transesophageal echocardiogram.
Figure 2.6. “Four-chamber” images and the central diagram illustrate a consistent approach to image orientation in the coronal plane. The three echocardiographic images shown here were obtained in very different ways. The transducer was placed at the cardiac apex, near the left anterior axillary line, to obtain the first image (bottom right). In contrast, the transducer was placed on the upper abdomen, below the xiphoid, to obtain the subcostal image (bottom left). The transesophageal echocardiographic probe was placed in the distal esophagus and the plane of sound entered the heart from behind to produce the last image (top left). Despite the variety of maneuvers and transducer positions, the images produced can easily be seen to demonstrate the same anatomic structures. TEE, transesophageal echocardiogram.
Figure 2.7. Coronal plane image obtained with the transducer at the suprasternal notch. It is oriented as if the patient were standing upright and facing the examiner. Therefore, superior structures are seen at the top of the screen and left-sided structures are to the observer’s right. To produce this image, the plane of sound has been angled posterior to the pulmonary arterial confluence, allowing visualization of the four pulmonary veins entering the left atrium. Each pulmonary venous orifice is marked by a numeral. The right upper pulmonary vein is marked by 1; right lower, 2; left lower, 3; and left upper, 4.The asterisk (*) is placed at the origin of the left atrial appendage. This image is often referred to as the “crab view” because the four pulmonary veins simulate the legs extending from the body of a crab (the left atrium). The aorta and main pulmonary artery are visualized in cross section superior to the atrial and venous structures. Ao, aorta; L, left; LA, left atrium; PA, pulmonary artery; S, superior.
Figure 2.8. Sagittal plane image obtained with the transducer at the suprasternal notch. The plane of sound cannot be directed in a completely superior–inferior direction from this position. However, because the plane of interrogation is closer to the body’s superior–inferior axis than it is to an anterior–posterior plane, the image is oriented as if the patient were standing “nearly” upright with the examiner to the patient’s left. Although the image is slightly tilted, superior structures are seen toward the top of the screen and anterior structures are toward the observer’s right. In reality, the apex of the sector represents the transition point between superior structures (top right) and anterior structures (top left). To produce this image, the plane of sound has been angled to the left, allowing visualization of the aortic arch and its brachiocephalic arterial branches. AAo, ascending aorta; DAo, descending aorta; LA, left atrium; P, posterior; RPA, right pulmonary artery; S, superior.
There are two primary advantages to using the image orientations just described. First, use of the apex-down orientations maintains a relatively consistent approach to the display of anatomy imaged in the sagittal, horizontal, and coronal planes, regardless of where the transducer is positioned (see Figs. 2.3, 2.5, and 2.6). Therefore, it becomes easier to determine and to understand the appropriate image orientations for nonstandard views. For example, coronal images taken from the cardiac apex in patients with dextrocardia (still a coronal apical four-chamber view) should be displayed with the apex-down and left-sided structures to the right. Such consistency of presentation is vital to understanding the complex anatomy found in some patients with congenital heart disease.
Figure 2.9. “Bicaval” views. These three images demonstrate similar anatomy. All are sagittal plane images focused on the atrial septum and the junctions of the superior and inferior venae cavae with the right atrium. Top left: The image was obtained from the subcostal transducer position. The plane of sound enters the body along a path at a slight angle to the true inferior–superior axis. Top right: Similarly, the plane of sound that created this high-right parasternal image traveled through the thorax at an angle to both the true superior–inferior and anterior–posterior planes. The subcostal image achieves a nearly vertical orientation and therefore is displayed as if the patient were upright. The more oblique nature of the right parasternal image requires the use of a hybrid of the two acceptable orientations for sagittal images. The apex of the sector represents the transition point between superior structures (top right) and anterior structures (top left). The asterisk (*) in the two top panels is positioned at the junction of the inferior vena cava and right atrium. The esophageal bicaval view (bottom) represents the ideal orientation for a sagittal image. The interrogating plane of sound crosses the chest in a nearly direct posterior–anterior route. It has been angled slightly to the right to produce this image. Anterior structures are at the top of the viewing screen and superior structures are seen to the observer’s right. Note: The thicker superior limbus of the atrial septum (seen clearly in the top left and bottom) will always be associated with the morphologically right atrium. The thinner, more inferior–posterior, component of the atrial septum (valve of the fossa ovalis) is a reliable marker for the position of the morphologically left atrium. Bottom: Position of the right atrial appendage (#). A, anterior; LA, left atrium; P, posterior; RA, right atrium; RPA, right pulmonary artery; S, superior; SVC, superior vena cava.
Second, nonechocardiographers (surgeons, nonimaging cardiologists) have difficulty understanding anatomy when it is displayed in a nonanatomic format. The widely used “apex-up” format simulates the anatomy of a patient who is standing on his or her head and facing away from the examiner. Therefore, apex-down imaging not only displays echocardiographic data in a more anatomic format, but also allows echocardiographers to communicate more effectively with their colleagues.
A last word about image orientation: The consistent approach described for the orientation of transthoracic images should also be applied to images obtained using other echo technology (transesophageal or intravascular). A simple way to achieve this while performing transesophageal echocardiography is to display all images (except the four-chamber view) with the “point” of the sector at the bottom of the video screen. This requires inverting the electronic image. Images that are recorded in this way will automatically display posterior structures (those close to the esophagus) at the bottom of the screen and place anterior structures at the top. The only exception to this rule is the esophageal four-chamber view. Here, one would want to leave the apex at the bottom of the image to maintain a consistent anatomic orientation. This would require the examiner to invert the image, placing the sector’s apex (and the atria) at the top of the screen.
NOMENCLATURE OF CONGENITAL HEART DISEASE
One of the areas of recent controversy in congenital cardiology concerns the language used to describe the anatomy of the heart and great vessels. Some cardiac morphologists and physicians, led by Professor Robert Anderson, have adopted language that uses English terms instead of the more classic Latin nomenclature. Unfortunately, this can create a great deal of confusion for those attempting to understand congenital heart disease. What follows is an attempt to define the terms used to describe congenital heart disease using the standard, Latin terms and the more recently proposed, but already widely adopted, Anglicized language.
Situs or Sidedness
This concept applies to structures/organ systems that are not bilaterally symmetric. It describes the position of the organs in the system and usually has three possible arrangements: normal or solitus, inverted or inversus (mirror image of normal), and ambiguous (something else).
Visceral Situs or Sidedness
■Solitus, or normal: Liver and cecum to the right, stomach and spleen to the left.
■Inversus, or inverted: Liver and cecum to the left, stomach and spleen to the right.
■Ambiguous: Any other patterns—frequently the liver is bilateral and there is intestinal malrotation; gastric position is variable (the spleen, when present, is always posterior to the stomach).
Atrial Situs or Sidedness
Also referred to as cardiac situs or sidedness. It is determined by the position of the morphologic right and left atria.
■Solitus, or normal: Morphologic left atrium is posterior and to the left of right atrium.
■Inversus, or inverted: Morphologic left atrium is posterior and to the right of right atrium.
■Ambiguous: Confident assignment of morphologic left and right atria cannot be made, usually in common atrium.
Cardiac Position (top, Fig. 2.10): This represents the gross position of “most” of the heart relative to the midline.
■Levoposition: Most of the cardiac mass is to the left of midline.
■Dextroposition: Most of the cardiac mass is the right of midline.
■Mesoposition: The heart is evenly distributed around the midline.
Cardiac Orientation (Fig. 2.10, lower panel): This represents the orientation of the base-to-apex axis of the heart, not its position within the mediastinum (although the two usually go together).
■Levocardia: Base-to-apex axis is “pointed” from upper right to lower left.
■Dextrocardia: Base-to-apex axis is “pointed” from upper left to lower right.
■Mesocardia: Base-to-apex axis is “pointed” nearly directly from superior to inferior and usually is in the midline.
The distinction between orientation and position is usually not important because they tend to go together. In other words, levopositioned hearts usually also have a leftward base-to-apex axis (levocardia). However, when other pathology (diaphragmatic hernia or unilateral lung hypoplasia) causes a shift in cardiac position, the difference between position and orientation can become significant. For example, most infants with left-sided diaphragmatic hernias have levocardia with dextroposition because the hernia has “pushed” a normal heart into the right chest.
Assessment of cardiac location is most efficiently performed using coronal plane imaging (four-chamber view) from the subcostal window. Figure 2.11 provides an example of the maneuver used to determine cardiac position and axis in a normal patient. The scan begins with a midline horizontal plane image of the upper abdomen (see left, Fig. 2.11). The plane of sound is maintained in the midline and angled superiorly (across the diaphragm) to a coronal view of the heart, usually in a four-chamber orientation (see middle, Fig. 2.11). Once the axis and position of the heart have been determined, the image is reformatted into a standard anatomic orientation (see right, Fig. 2.11). Figure 2.12 illustrates the same sweep from a patient with osteogenic sarcoma, in whom the tumor has shifted the heart into the right hemithorax. Despite the abnormal position, it is clear that the base-to-apex axis is still slightly oriented to the left, resulting in a case of dextroposition with levocardia.
TERMS USED TO DESCRIBE CARDIOVASCULAR SEGMENTS AND CONNECTIONS
Segment: Section of the cardiovascular system (i.e., great veins or the ventricles).
Connections: Junction between two cardiovascular segments.
Overriding: Function of a valve annulus and a VSD. The term describes an annulus that crosses the plane of a VSD and is therefore “over” more than one ventricle. Any of the cardiac valves can potentially be described as overriding.
Figure 2.10. Difference between the concepts of cardiac position and cardiac orientation. Cardiac position is determined only by the overall location of the heart relative to the anatomic midline (top). It has no relationship to the internal organization of the cardiac structures. If the majority of the heart is to the left, then the heart is in levoposition. Conversely, if most of the heart is to the right of the midline, then we refer to the patient as having dextroposition. When the heart is located centrally in the chest, the patient is said to have meso- or midline position. Determination of cardiac orientation requires knowledge of the internal arrangement of the heart. Orientation refers to the right–left direction of the so-called base-to-apex axis. The apex of the heart is the ventricular apex, and the base is at the great arterial origin(s). The normal base-to-apex axis is directed inferiorly and to the left (bottom right). This orientation is referred to as levocardia. When the heart is vertically oriented and in the midline, the apex is directly inferior to the base. This situation is illustrated by the central diagram in the bottom panel and is referred to as mesocardia. The diagram on the bottom right illustrates the concept of dextrocardia. In this situation, the cardiac apex is inferior and to the right relative to the base. Clinically, most patients will have concordant cardiac positions and orientations. In other words, hearts with levoposition will also display a leftward base-to-apex axis (levocardia). However, extracardiac processes can shift the cardiac position, resulting in discrepancies between position and orientation.
Straddling: Function of the chordae tendineae of an AV valve and a VSD. The term describes chordae that cross a VSD and have their myocardial attachments within the opposite ventricle. This can create difficulties for the surgeon trying to close a VSD. An AV valve can both straddle and override, but a semilunar valve cannot straddle because it does not have chordae.
Concordant: This refers to a normal connection between segments. For example, when the right atrium connects to the right ventricle, the connection is described as concordant.
Discordant: This refers to the opposite of the normal connection. For example, when the left ventricle connects to the pulmonary artery, the connection is discordant.
Univentricular: A special form of AV connection in which all atria are committed to only one functional ventricle.
Figure 2.11. Normal cardiac orientation and axis. This series of images were obtained from the same patient and demonstrate the determination of cardiac position and axis. Left: This image is a subcostal horizontal plane view of the upper abdomen. The apex of the sector is positioned in the midline. The liver and inferior vena cava (IVC) are seen on the patient’s right. The aorta (Ao) and stomach (St) are to the patient’s left. Middle: This image was obtained by angling the interrogating plane of sound superiorly into the chest. The apex of the sector was maintained in the midline (yellow dotted line). Most of the cardiac structures are to the left of the patient’s midline, including the cardiac (ventricular) apex. This confirms the presence of both levoposition and levocardia. The apex-up image (middle) is used only to confirm cardiac position and axis. Once this determination is complete, we can reorient the image into the more anatomic format (right). The two echocardiographic images (bottom) illustrate the different appearances of levocardia (right) and dextrocardia (left) when associated with congenital heart disease. Both images were obtained from the subcostal transducer position and demonstrate four-chamber coronal views. Left: This image was taken during examination of the patient with atrioventricular discordance, ventricular septal defect, and pulmonary stenosis. The majority of the heart is to the right of the midline. Chamber enlargement has rotated this heart into a nearly horizontal orientation. The apex (asterisk) is clearly to the right of the base, consistent with dextrocardia. Right: This image was taken from an examination of a patient with tricuspid valve atresia. In this case, both cardiac orientation and position are normal (leftward). The cardiac apex (asterisk) is to the left and inferior to the cardiac base, consistent with levocardia. A, anterior; L, left; LA, left atrium; LV, left ventricle; mLV, morphologically left ventricle; mRA, morphologically right atrium; mRV, morphologically right ventricle; RA, right atrium; RV, right ventricle; S, superior.
Transposition: The prefix trans- means “across,” in this case “across the septum.” Therefore, transposition refers to the semilunar valves only and occurs when the great arteries (and therefore the semilunar valves) are on the opposite side of the ventricular septum relative to normal (aorta on the morphologically right ventricular side of the septum and pulmonary artery on the morphologically left ventricular side).
Malposition: This term also refers to the semilunar valves and great arteries. It is applied to any position/connection of the great arteries to the ventricles that is not normal and not transposition. For example, the great arteries are always malpositioned in a double-outlet right ventricle, and the term “transposition” should never be applied to a double-outlet right ventricle because the great arteries are on the same side of the septum (not “across” it).
Superior vena cava = superior caval vein
Inferior vena cava = inferior caval vein
Foramen ovale = fossa ovalis = oval fossa
Endocardial cushion defect = AV canal defect = AV septal defect
Truncus arteriosus = persistent truncal artery
Ductus arteriosus = ductal artery
Figure 2.12. Levocardia with dextroposition. These subcostal images were obtained during an examination of the patient with thoracic osteogenic sarcoma. The tumor is visualized above the diaphragm in both images. Left: Normal spatial arrangement of the organs in the upper abdomen. The stomach is not as apparent as usual due to the presence of the tumor near the left diaphragm. The abdominal aorta (Ao) has been shifted slightly to the right but is still generally recognizable as a left-sided structure. As the plane of sound is swept superiorly to reveal the heart (right), it is obvious that the majority of the cardiac chambers lie to the right of the midline (yellow dotted line). This represents a situation in which there is dextroposition due to an extracardiac mass occupying most of the left hemithorax. The cardiac base-to-apex axis remains slightly leftward, despite the positional shift that has occurred. A, anterior; IVC, inferior vena cava; L, left.
SEQUENTIAL SEGMENTAL ANALYSIS OF CARDIOVASCULAR ANATOMY AND CONGENITAL CARDIAC MALFORMATIONS
One of the more intimidating aspects of congenital heart disease is the large number and broad spectrum of anomalies that can be found in a single patient. As a result, congenital cardiologists have developed a standardized approach to the description of cardiovascular anatomy and pathology. This process has been called the “sequential segmental approach” to congenital heart disease. Simply described, this approach divides the patient’s cardiovascular system into a sequence of individual segments and the connections between those segments (Fig. 2.13). One then describes the position, anatomy, and function of all the structures within each segment, as well as the connections between the segments. Using this approach, one can be confident that a complete assessment has been obtained even in the most unusual cases. In the setting of very complicated anomalies, this type of rigorous and organized approach becomes essential. This is not to say that every echocardiographic examination follows the sequence of the segmental approach. Image acquisition still follows the pattern described earlier in this chapter. Segmental analysis is not a physical action but rather a thought process that provides the congenital echocardiographer with a checklist or framework for categorizing any cardiovascular malformation.
Figure 2.13. Sequential segmental analysis of cardiovascular anatomy.
DETERMINATION OF CARDIAC LOCATION AND SITUS (SIDEDNESS)
Before specifically describing the structures that are found within the cardiovascular segments, the general positions of the major thoracic and abdominal organ systems must be defined. In congenital cardiology, one must specifically describe the position and orientation of the heart within the chest and the positions of the two major organ groups that affect the location of cardiovascular structures. These organ groups are (a) the abdominal viscera and (b) the atria. Each of these organ groups has an asymmetric arrangement of their structures and therefore can be described as having situs (or sidedness). In other words, the right half of the organ group is not the same as the left. The nomenclature describing these asymmetric organ groups, cardiac position, and orientation was described in the preceding section.
The echocardiographic assessment of abdominal (or visceral) situs focuses on the positions of the liver, stomach, spleen and abdominal great vessels, aorta, and inferior vena cava. Horizontal plane images of the upper abdomen are most useful for most of this assessment, although the spleen is more easily seen from the flank (lateral and posterior to the stomach). Examples of three common abdominal patterns are shown in Figure 2.14. When the liver and inferior vena cava are to the right and the stomach, spleen, and abdominal aorta are to the left, the patient has abdominal situs solitus. Abdominal situs inversus is just the opposite, with the stomach, spleen, and aorta to the right and the liver and inferior vena cava to the left. There are several recognized forms of abdominal situs ambiguous. The most common ambiguous pattern is seen in the asplenia syndrome. There is a large midline liver. The inferior vena cava and aorta are located on the same side of the spine (can be right or left). Stomach position is variable and the spleen is absent. In this setting, some of the hepatic veins may connect directly to the atrium instead of entering the inferior vena cava. These independently connecting veins are important to identify because they need to be incorporated into the systemic venous pathway of a modified Fontan procedure.
Atrial situs, sometimes referred to as cardiac situs, refers to the arrangement of the atria. In atrial situs solitus, the morphologically right atrium is located anterior and to the right of the morphologically left atrium. Atrial situs inversus results in the morphologically right atrium being to the left of (but still slightly anterior to) the morphologically left atrium. True atrial situs ambiguous is rare. When present, it is usually associated with a large common atrium in which there are no clear differences between the right and left portions of the atrium. This is most often seen in patients with asplenia, and the two halves of the common atrium both tend to resemble a morphologically right atrium.
To distinguish a morphologically right from a morphologically left atrium, a variety of anatomic landmarks can be used. The most reliable is the anatomy of the atrial septum (Fig. 2.15). The thicker limbus of the foramen ovale is always located on the same side of the septum as the morphologically right atrium. Conversely, the thin valve of the foramen ovale is always on the same side as the morphologically left atrium. This information can be most clearly visualized in subcostal, right parasternal, or esophageal images of the atrial septum (Fig. 2.16).
Figure 2.14. Different spatial arrangements of the upper abdominal viscera. Left: Normal anatomy. The central image was taken during examination of the patient with the polysplenia syndrome and shows an arrangement of the abdominal organs that is the mirror image of normal. The liver, abdominal aorta (Ao), and azygos vein (Az) are all found to the patient’s left. The stomach (St) and the hepatic venous confluence (HV) are on the patient’s right. This arrangement is consistent with abdominal situs inversus, or mirror image sidedness. The azygos vein is quite prominent in this case, because there was interruption of the inferior vena cava. Right: This image was obtained during the examination of a newborn with asplenia syndrome, subdiaphragmatic total anomalous pulmonary venous connection, and bilateral inferior venae cavae. The spatial arrangement of the abdominal organs in this case is “ambiguous.” The liver is found in both upper quadrants; the stomach was found to be right-sided. When scans of the upper abdomen reveal unusual spatial relationships of the liver, stomach, and abdominal great vessels (middle and right), the examiner is alerted to the fact that the patient’s cardiovascular anatomy is also likely to be complex. A, anterior; APVn, anomalous pulmonary vein; IVC, inferior vena cava; L, left; V, vertebral body.
Figure 2.15. Anatomic specimens display features that distinguish the morphologically right from the morphologically left atrium. Left: The four-chamber view shows the normal arrangement of the atrial septum. Note that the thicker, muscular limbus (yellow arrows) is positioned to the right. The presence of this limbus is the most reliable echocardiographic marker associated with the morphologically right atrium. Just to the left of the thick limbus is the thin fossa ovalis membrane (black arrow). This thin segment of the atrial septum was the “flap valve” of the fetal foramen ovale and is always associated with the morphologically left atrium. When the atrial septum is absent, other anatomic features must be relied on to distinguish the morphologically right atrium from the morphologically left atrium. The specimens to the right of the white line are the free walls and appendages of a normal, morphologically right atrium (specimen in the center of the figure) and a normal, morphologically left (specimen on the far right) atrium. The right atrium is far more muscular than the left. There are a series of pectinate muscles radiating outward from a thick muscular ridge, called the Christa terminalis (black arrowhead). These muscular ridges are absent from the morphologically left atrium because it is derived primarily from the common pulmonary vein. Note the smooth walls present in the body of the left atrium. These features are often difficult to assess echocardiographically especially when the chambers are enlarged. If the atrial septum does not provide adequate information to assign atrial morphology, the next most reliable echocardiographic marker for the position of the morphologically right atrium is the entrance of the coronary sinus and/or the suprahepatic inferior vena cava (IVC). This segment of the IVC will always relate to either to the right atrium or the coronary sinus. Historically, cardiologists had focused on the shape of the atrial appendages (asterisks) to distinguish atrial morphology. The morphologically right atrium generally has a broad-based, pyramidal appendage. In contrast, the left atrial appendage is narrower and often has multiple small side lobes (as in this figure). The left atrial appendage has also been described as “finger-like,” because of its narrow base. Unfortunately, the shape of the appendages can change, especially with chamber dilation. As a result, appendage shape is less reliable than the other features listed here.
Unfortunately, in patients with large atrial septal defects, this landmark is absent. In others with suboptimal image quality, one may not be able to resolve the septum well enough to make this distinction. In these situations, we rely on the connection of the coronary sinus, suprahepatic portion of the inferior vena cava, the size and shape of the atrial appendages, and/or the pattern of the atrial wall (muscular or not) to determine which atrium is which. The coronary sinus, when present, will always connect to the morphologically right atrium. The suprahepatic portion of the inferior vena cava (upstream from the entrance of the hepatic veins) will also almost invariably connect to the morphologically right atrium. The only times that these findings become difficult to interpret are when the inferior vena cava connects to one side of an atrium and an independently connecting hepatic vein connects to the other, or the inferior vena cava connects to an unroofed coronary sinus. The connection of the superior vena cava is not a reliable indication of atrial morphology.
The atrial appendages have also been used to identify atrial situs. The appendage of a morphologically right atrium tends to be broad, somewhat pyramidal in shape. In contrast, the morphologically left atrial appendage is usually smaller and more “finger-like” (see Fig. 2.15). When using these criteria, one must remember that atrial dilation and/or hypoplasia can distort the size and shape of either appendage. The last and least reliable feature involves the atrial walls. The morphologically right atrium has coarse, muscular appearing walls due to its pectinate muscles and the crista terminalis. The morphologically left atrium, because it is derived primarily from the common pulmonary vein, has a smoother appearance to its walls. Although these differences are quite clear to the pathologist, echocardiographically, they are rather subjective and understandably less reliable than the other features used to determine atrial situs.
Figure 2.16. Normal anatomy of the atrial septum in a patient with normal cardiac situs (sidedness). Left: Subcostal, bicaval view. The superior, thicker limbus of the atrial septum is seen on the right (asterisk). Even without knowledge of other anatomic features, this confidently classifies the right-sided atrial chamber as a morphologically right atrium in this case. Right: Also a bicaval view but obtained from the distal esophageal transducer position during transesophageal echocardiography. The asterisk (*) again marks the position of the thick superior limbus. The thinner “flap valve” of the atrial septum is found posterior to the limbus. This relationship identifies the anterior chamber as the morphologically right atrium and the posterior chamber as the left atrium. LA, left atrium; RA, right atrium; RPA, right pulmonary artery; SVC, superior vena cava.
SEGMENTS AND CONNECTIONS
Once the cardiac location, orientation, and situs have been determined, the echocardiographer then examines each of the cardiovascular segments and the connections between them. Because the determination of location and situs was made using the subcostal transducer position, the remainder of the examination usually begins in that position and progresses from there to the parasternal, apical, and suprasternal views in a sequential fashion. Obviously, multiple segments and connections can, and should, be interrogated from each window. Furthermore, information obtained from one plane of imaging may prompt a return to a previous window to clarify or reexamine a finding. Therefore, while our thought processes follow the segmental approach toward a final diagnosis, the scans providing the information may not. Nevertheless, for the purposes of this discussion, we will assume that both our thoughts and our scans will follow a segmental path toward the final diagnosis.
The examination of each segment must describe the anatomy, function, and physiology (i.e., shunts, stenoses, etc.) present within it. In addition, and sometimes most important, the connections between segments must be described. Connections can be concordant (normal) or discordant (opposite of normal). In some situations, other designations are needed for connections that are not normal but are also not the opposite of normal (i.e., double-outlet right ventricle or univentricular AV connection).
The Venous Segment
Both systemic and pulmonary venous anomalies play important roles in the presentation and treatment of congenital heart disease. The systemic veins that we are most concerned with are the inferior and superior venae cavae, the coronary sinus, and the hepatic veins. The inferior vena cava and hepatic veins are imaged from the subcostal position. Horizontal plane scans that progress gradually from the infrahepatic region of the upper abdomen toward the diaphragm provide the best delineation of these structures. Normally, veins draining both the right and left lobes of the liver can be easily identified and followed to their connections to the inferior vena cava. The inferior vena cava will then be seen to enter the morphologically right atrium, just posterior to the Eustachian valve. In cases where one or more hepatic veins connect to the morphologically right atrium independently, the anomalous vein will travel in a more superiorly directed course than normal and will enter the morphologically right atrium through a separate orifice. These independently connecting veins will usually, but not always, enter the morphologically right atrium near the orifice of the true inferior vena cava. Patients with interruption of inferior vena cava (frequently associated with the polysplenia syndrome) will have a large azygos vein, seen along the spine in the abdomen. This vessel can be either right- or left-sided and will enter the superior vena cava within the thorax, allowing inferior venous return to reach the heart. In this situation, there will still be a vein (or veins) entering the floor of the morphologically right atrium. This vessel is the “suprahepatic inferior vena cava” that was mentioned in the discussion of atrial situs. This vessel can be distinguished from a normal inferior vena cava by its generally smaller size and by the fact that it does not extend inferior to the liver. It should be noted that in defining the anatomy of these veins, one has simultaneously described their venoatrial connections.
Venous drainage from the upper body usually is directed to a single, right-sided superior vena cava and from there to the right atrium. A right-sided superior vena cava can be visualized in several planes from the subcostal window (see Fig. 2.16), high parasternal views, or the suprasternal notch. It is not generally seen from the apex. One of the most common variations in systemic venous anatomy is the persistence of a left-sided superior vena cava, resulting in the presence of bilateral great veins from the upper body. When present, a left superior vena cava will usually connect to the coronary sinus at the posterior/lateral border of the left atrium (Fig. 2.17). Therefore, a clue to the presence of a left superior vena cava is dilation of the coronary sinus (due to the increased flow passing through it). Direct visualization of the left superior vena cava can be obtained in a long-axis plane—where it is seen coursing superiorly from the coronary sinus into the upper left mediastinum. In parasternal short-axis images, the left superior vena cava appears as a circular vessel just anterior to the left pulmonary artery, near the pulmonary artery bifurcation (see Fig. 2.17). When abnormalities of situs exist, superior vena caval connections are frequently abnormal. Bilateral superior venae cavae may be present and both may connect directly to the superior aspect of the atria due to absence of the coronary sinus. In other patients, there may be only one superior vena cava present. Unfortunately, it is difficult to predict which superior vena cava will persist in these patients.
Similar to the systemic veins, the pulmonary veins can be seen in a number of views. The most useful images tend to be from the subcostal, apical, and suprasternal coronal planes (see Fig. 2.7). Color flow Doppler is often helpful in defining the position of the pulmonary veins and distinguishing them from the atrial appendage. Most patients have four pulmonary veins, two from each lung. However, variations from this pattern can still be normal. The left veins frequently join before entering the atrium, resulting in only three venous entries at the atrial level. Alternatively, the most common variant of right pulmonary veins is for there to be three separate veins connecting to the atrium.
There are two general categories of anomalous pulmonary venous connection: total and partial. Total anomalous connection of the pulmonary veins is further subdivided into supracardiac, cardiac, and infradiaphragmatic types. The anatomy and echocardiographic features of both partial and total anomalous connections have been extensively described elsewhere.
The Atrial Segment
We have already discussed the features that distinguish a morphologically right atrium from a morphologically left atrium. In addition to the size and position of each atrium, the status of the atrial septum requires definition when describing the atrial segment. The assessment of atrial septal defects is discussed in Chapter 6.
The Atrioventricular Connection
There are a large number of terms used to describe the spectrum of AV connections that exist in patients with congenital cardiac malformations. This creates at least some degree of unnecessary confusion. If one uses a simple description of the connection, most of the confusion can be avoided (Figs. 2.18 and 2.19). The first point should be to define whether there is a biventricular or univentricular connection. In biventricular hearts, the connection will usually be composed of two AV valves. These valves will then connect the atria to the ventricles in either a concordant (or normal) or discordant (opposite of normal) manner (see Fig. 2.18). A concordant AV connection exists when the morphologically right atrium connects to the morphologically right ventricle through a tricuspid valve and the morphologically left atrium connects to the morphologically left ventricle through a mitral valve. AV discordance implies that the morphologically right atrium connects to the morphologically left ventricle. When it does, the valve associated with this connection will always be a morphologically mitral valve. The morphologically left atrium will then connect to the morphologically right ventricle through a morphologically tricuspid valve.
Figure 2.17. Common echocardiographic presentation of a left-sided superior vena cava. Top: Parasternal long-axis image, Blue arrow points to an enlarged coronary sinus. This is often the first indication of a persistent left superior vena cava (LSVC). Bottom: High parasternal images that directly visualize the LSVC. Bottom left: Sagittal plane view parallel to the long axis of the LSVC (yellow arrow). Bottom right: Horizontal plane view of the LSVC (yellow arrow) at the level of the pulmonary arterial confluence (PA). Both images reveal that the LSVC is positioned anterior to the left pulmonary artery (LPA). The sagittal plane image (bottom left) also shows that this vessel passes posterior to the left atrial appendage (asterisk) and anterior to the left pulmonary veins before merging with the coronary sinus. Ao, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; PVeins, pulmonary veins.
Figure 2.18. Three potential atrioventricular connections seen with biventricular circulations. The connection is normal and described as concordant (left) when the morphologically right atrium connects to the morphologically right ventricle, and vice versa. The two other connections in this illustration are abnormal. Middle: Discordant atrioventricular connections, with the morphologically right atrium associated with the morphologically left ventricle. Conversely, the morphologically left atrium is connected to the morphologically right ventricle in this case. The septal insertions of the two atrioventricular files provide an excellent echocardiographic marker of this connection. This will be illustrated further in the subsequent figures. Far right: Ambiguous connection that is difficult to assign. There is a common nature atrioventricular valve with no attachments to the septum, the atrial septum is absent, and the atria appear anatomically similar. In these situations, one must rely on the connection of the coronary sinus and suprahepatic inferior vena cava to determine the position of the morphologically right atrium. Occasionally, even this criterion is difficult to apply (bilateral hepatic veins or inferior cavae). In these complex hearts, it is better to simply describe the anatomy of the heart and function of the valves and chambers and refer to the connection as ambiguous. AV, atrioventricular; LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.
Figure 2.19. Three of the potential atrioventricular (AV) connections associated with univentricular circulations. These connections are described based on the number and type of atrioventricular valve(s) that are related to the dominant ventricle. Left: Two separate atria, each with its own atrioventricular valve, that connect to a single ventricular cavity. This connection is described as a double inlet, univentricular AV connection. Middle: This diagram shows a situation in which there is atresia of one atrioventricular valve. This connection exists in both tricuspid and mitral atresia. When the anatomy does not fall simply into one of these two categories, the connection is described as a single inlet, univentricular AV connection. The diagram is an example of a single inlet with right atrioventricular valve atresia (a.k.a. tricuspid atresia). Right: This univenticular connection involves a common atrioventricular valve serving as a single outlet/inlet from/into both atria and a single functional ventricular chamber. This occurs in a variety of situations including the heterotaxy syndromes.
The type of connection present in a biventricular heart is most easily defined using a four-chamber view. The internal cardiac crux (the area at which the septal leaflets of both AV valves insert) is asymmetric. At the annulus, the septal leaflet of the morphologic tricuspid valve will always insert at a point that is slightly apical to the insertion of the septal component of the mitral valve (Figs. 2.18 and 2.20). Because the AV valves are invariably associated with their appropriate ventricle (mitral with the left ventricle and tricuspid with the right ventricle), the internal crux can be used not only as a marker for AV connection but also for defining ventricular morphology. Occasionally, the AV connection in a biventricular heart will involve a common valve, as in the complete form of AV septal defect. In these cases, one can think of the connection as ambiguous because the internal crux cannot be used. Alternatively, one can rely on the positioning of the atria relative to the ventricular inflow to define the connection. An atrium with an “outflow” orifice positioned more than 50% over one ventricular inflow tract is, by convention, said to be committed or connected to that ventricle (Fig. 2.21). The appropriateness of the connection is then determined by the morphology of the two chambers in question (see sections on atrial and ventricular segments).
Univentricular connections are more variable. However, they can still be described in a straightforward way. When there is only a single functional ventricle, there can be a double-inlet, single-inlet, or common-inlet connection. The dominant ventricular morphology is usually described in conjunction with the classification of the AV connection. For example, the most common forms of univentricular AV connections are found in patients with hypoplastic left heart syndrome and tricuspid atresia (Figs. 2.22 and 2.23). These connections can be thought of as “single-inlet univentricular connections with atresia of one atrioventricular valve.” Although this seems to be a cumbersome designation for tricuspid atresia, the true utility of this approach becomes apparent in more complex patients. A diagnosis such as “common-inlet univentricular connection to a dominant right ventricle” clearly describes the anatomy present, even to those unfamiliar with these malformations or unaware that many patients with this type of connection have a heterotaxy syndrome.
Functional assessment of the AV connection consists primarily of defining the status of the valves in terms of hypoplasia, obstruction, and/or stenosis. Again, more complete descriptions of these evaluations are found in the appropriate chapters later in the text.
The Ventricular Segment
Obviously, it is important to initially define whether the patient has biventricular or functionally univentricular anatomy. In patients with biventricular hearts, the most reliable feature distinguishing a morphologically right ventricle from a morphologically left ventricle is the asymmetric arrangement of the internal cardiac crux (the septal insertions of the two AV valves). If this landmark is unavailable or difficult to visualize, one then relies on the inherent differences in the myocardial structure of the ventricles (see Figs. 2.22 and 2.23). A morphologically right ventricle will have coarse apical trabeculations and a moderator band (see Fig. 2.22). The morphologically left ventricular apex will have a relatively smooth endocardial surface (see Fig. 2.23). There are multiple, small papillary muscles associated with the AV valve support apparatus in a morphologically right ventricle, and some of the chordae will insert directly onto the ventricular septum. In a morphologically left ventricle, the papillary muscles will be large and discrete (see Fig. 2.23). In addition, there will usually be only two papillary muscles (univentricular hearts of left ventricular type may have four papillary muscles). The AV valve support apparatus in a morphologically left ventricle does not insert onto the ventricular septum, unless there is a common valve. In terms of relative position, the right ventricular outflow tract will always be the most anterior ventricular structure in the heart, even in patients with congenitally corrected transposition of the great arteries. Many authors have used shape to distinguish between the ventricles. A normal morphologically right ventricle is somewhat crescent shaped and the normal morphologically left ventricle is round in the short-axis plane and somewhat bullet shaped three-dimensionally. However, these shapes can be altered dramatically by pressure or volume overload (not to mention positional anomalies). Therefore, ventricular shape is probably the least reliable feature available to determine ventricular morphology.
In the functionally univentricular heart, many of these criteria are not available. In this setting, the most reliable way to determine ventricular morphology is to determine the type of “rudimentary ventricle” present. Patients with single ventricles of the right ventricular type will have a hypoplastic left ventricular remnant that is positioned posterior to the main ventricular chamber. These left ventricular remnants usually do not connect to great arteries and are generally very small (see Fig. 2.22). The findings characteristic of a morphologically right ventricle (coarse apical trabeculation and chordal insertions onto the septum) will still be present. However, they will often be difficult to detect with certainty because of coexisting chamber enlargement and myocardial hypertrophy. In a univentricular heart of left ventricular type, the rudimentary right ventricle will be found anteriorly and, unlike the rudimentary left ventricle, will frequently connect to a great artery.
Figure 2.20. Echocardiographic anatomy associated with normal and discordant atrioventricular connections and focus on the septal insertions of the two atrioventricular valves (white arrows). Left: Images from patients with normal hearts. The right atrium relates to the right ventricle, and the left atrium, to the left ventricle. Bottom left: Magnified image is centered on the insertions of the septal tricuspid leaflet (STL) and the anterior mitral leaflet (AML) at the internal cardiac crux. The STL will always attach to the ventricular septum at a point that is slightly apical to the insertion of the AML. This offset between the septal insertions can be used to reliably identify the morphology of the atrioventricular valves. Because these valves developed from the ventricular myocardium, this relationship can also be used to identify the morphology of the ventricle that is associated with the atrioventricular valve. Right: Example displays the relationships seen in a patient with congenitally corrected transposition of the great arteries. The atrioventricular connections are discordant. The right atrium is associated with a right-sided but morphologically left ventricle. The valve connecting these two chambers is a morphologically mitral valve as evidenced by the basal position of its septal insertion. Conversely, the left atrium is related to a left-sided, morphologically right ventricle. The atrioventricular valve on the left is morphologically a tricuspid valve. Its septal insertion is apically positioned relative to the valve on the opposite side of the septum (white arrow). Although this finding alone identifies that the chamber and valve morphologically have a right ventricle and tricuspid valve, this conclusion is confirmed by the presence of a moderator band at the apex of the left-sided morphologically right ventricle (asterisk). AV, atrioventricular; L, left; LA, left atrium; LV, left ventricle; mLV, morphologically left ventricle; mRV, morphologically right ventricle; RA, right atrium; RV, right ventricle; S, superior.
Figure 2.21. The 50% rule. Assignment of the atrioventricular and ventriculoarterial connection in the presence of the ventricular septal defect (VSD) and annular override. The valvar annulus may not be perfectly aligned with the ventricular chamber in patients with a septal defect. When a valve annulus overlies more than one ventricle, it is said to override the VSD. In these cases, we assign the connection of the valve and its proximal atrium or distal artery to the ventricle over which more than half (50%) of the annulus is found. The diagram illustrates this concept for two atrioventricular valves that override inlet VSDs. Left: Example shows a right atrium with a valve that is more than 50% committed to the right ventricular inlet. Therefore, despite the override, the atrioventricular connection is concordant. Right: In contrast, the valve associated with the right atrium has an annulus that is primarily committed to the left ventricular inlet. As a result of this severe override, the atrioventricular connection is now discordant (the right atrium is committed to the left ventricle). AV, atrioventricular, LV, left ventricle, RA, right atrium, RV, right ventricle.
The examination of the ventricular segment must also include assessment of the ventricular septum and ventricular function. These topics are well covered later in the text.
The Ventricular–Great Arterial Connection
Similar to the assignment of the AV connection, there are several types of ventricular–great arterial connections. Concordant connections imply that the morphologically left ventricle gives rise to the aorta and the morphologically right ventricle connects to the pulmonary artery. Discordant connections are characterized by the pulmonary artery arising from the morphologically left ventricle and the aorta originating from the morphologically right ventricle. It should be noted that there are no anatomic features of the semilunar valves themselves that can be used to make these assignments. The aortic and pulmonary valves are anatomically identical. Therefore, the “morphology” of the valve is determined by the downstream artery. So, a semilunar valve that is connected to the pulmonary arteries becomes the pulmonary valve, and the valve in continuity with the aorta, the aortic valve.
When VSDs are present, the assignment of both the AV and ventriculoarterial connections can be more difficult. In this setting, the simplest rule to follow has been called the “50% rule.” This “rule” can be applied to both connections and states that if a valve annulus overlies a ventricular cavity by 50% or more, then it is assigned to the ventricular cavity that is associated with the majority of the annulus. Figure 2.21 shows this relationship for two AV valves. This assignment is best made using the apical four-chamber view in most cases. The same process can be applied to the semilunar valves. However, the parasternal long-axis projection provides the optimal visualization of these relationships (Fig. 2.24). Ventriculoarterial connections can be more difficult to assign from the subcostal window (Fig. 2.25). Careful definition of the plane of the ventricular septum is required to use the 50% rule accurately from this transducer position. An additional useful anatomic clue for assigning the left ventricle to an arterial connection is the presence of fibrous continuity between a semilunar valve and the morphologically mitral valve. The semilunar valve that originates from the left ventricle will usually (but not always) be in direct continuity with the anterior hinge of the morphologically mitral valve.
Figure 2.22. Determining ventricular morphology in hearts with univentricular circulations (morphologically right ventricles). These echocardiographic images were taken from an infant with hypoplastic left heart syndrome. Top: Subcostal “four-chamber” view of this heart. The right ventricle (RV) is supporting the systemic circulation and has become enlarged and hypertrophied. As a result, the anatomic features normally associated with right ventricular morphology are not as easily appreciated. The severe abnormality of the mitral valve makes determination of the septal offset difficult. In these situations, we rely on the fact that a morphologically tricuspid valve and right ventricle will display atrioventricular chordal attachments to the ventricular septum, the presence of a moderator band in the right ventricular apex (not seen here), and the relationship of the dominant ventricle to the hypoplastic ventricular remnant. In this case, there were septal chordal attachments of the only sizable atrioventricular valve, and the hypoplastic ventricular remnant (*) was posterior to the dominant ventricle. This spatial relationship alone identifies the dominant ventricle as a morphologically right ventricle. Bottom:Classic arterial anatomy associated with hypoplastic left heart syndrome. Left: Main pulmonary artery (PA) continuing through the “ductal arch” (DA) to supply flow to the aortic circulation. Right: Diminutive descending aorta (white arrow) just anterior to the right pulmonary artery (RPA). L, left; LA, left atrium; RA, right atrium; RV, right ventricle; S, superior.
Figure 2.23. Determining ventricular morphology in hearts with univentricular circulations (morphologically left ventricles). The echocardiographic images in this figure were taken during examinations of patients with tricuspid valve atresia (top) and a univentricular heart with left ventricular morphology and double-inlet atrioventricular connection, the so-called double-inlet LV. Because the anatomy of the internal cardiac crux lacks the asymmetry of the biventricular heart, one must rely on other anatomic markers to determine ventricular morphology. The ventricular chamber can be seen in multiple planes. In both of these cases, the ventricles have a relatively smooth endocardial lining and large discrete papillary muscle groups (top right) that do not attach to the ventricular septum. However, the most reliable indicator that the dominant ventricle is a structurally left ventricle is the anterior position of the hypoplastic right ventricular remnant (asterisk in the bottom right image). Top left: Area of the expected, but absent, right atrioventricular connection (white arrow). A, anterior; L, left; LA, left atrium; LV, left ventricle; RA, right atrium; S, superior.
Some complex forms of congenital heart disease will have the absence of one great arterial connection (i.e., pulmonary atresia or truncus arteriosus). Others will result in both great arteries originating from the incorrect ventricle or even the same ventricle, most commonly a morphologically right ventricle (see Fig. 2.25). In these cases, the spatial relationship of the aorta must be described relative to the pulmonary artery and valve, as well as any VSDs that may be present. For example, in AV concordance with VA discordance (complete transposition of the great arteries), the aorta is usually found anterior and to the right of the pulmonary valve. This can be referred to simply as “AV concordance with VA discordance and an anterior and rightward aorta.”
The relationship of the great arteries to the VSD is most important in cases of double-outlet right ventricle, because this relationship will in large part determine the type of surgical repair. Subaortic and “double-committed” VSDs can be repaired using a relatively simple patch technique. Patients with double-outlet right ventricle and a subpulmonary VSD require more complex surgical maneuvers, involving either a Rastelli approach (intraventricular baffle, right ventricle-to-pulmonary artery conduit, and ligation of the native main pulmonary artery) or an arterial switch operation to achieve a biventricular repair. VSDs that are “remote” from both great arteries present perhaps the greatest surgical challenge and may be more appropriately treated with a Fontan protocol as if they were a univentricular heart.
Figure 2.24. Echocardiographic images demonstrate normal (concordant) left ventricular to aortic connection (left and middle). Left: There is no ventricular septal defect, and thus the connection is unambiguous. Middle: Taken from the examination of an infant with tetralogy of Fallot. The aortic annulus is centrally positioned above an outlet for ventricular septal defect (asterisk). There is roughly 50% of the aortic annulus committed to each ventricle, a common situation in patients with tetralogy. The muscular ventricular septum is almost perfectly aligned with the central coaptation point of the aortic valve leaflets. In this situation, we assign the aortic connection to the left ventricle because there is no conal muscle separating the posterior hinge point of the aortic valve from the anterior hinge of the mitral valve (fibrous continuity). Right: The long-axis image was taken during an examination of the patient with double-outlet right ventricle (DORV). Here, there is no evidence of a semilunar valve near the anterior hinge point of the mitral valve. Instead, the aorta (Ao) is positioned anterior to the ventricular septal defect and is completely separated from the left ventricle and mitral valve by infundibular/conal muscle (arrow). As a result, the aortic valve connection is assigned to the right ventricle. The pulmonary valve also arose from the right ventricle and was positioned even farther from this subaortic ventricular septal defect. LA, left atrium; LV, left ventricle; RV, right ventricle.
As with all of the preceding components of the segmental approach, the status, anatomy, and function of each connection (i.e., semilunar valve) must be specifically examined and described.
The Great Arterial Segment
Descriptions of this segment are relatively self-explanatory. Individual vessels that must be examined include the aorta, pulmonary arteries (main, right, and left), coronary arteries (usually limited to the left main, and the proximal parts of the left anterior descending, circumflex, and right coronary arteries), and ductus arteriosus. Complete assessment describes the presence/absence, size, origin, position, and any dilations or stenoses of these arteries.
Because the echocardiographic evaluation of a patient with congenital heart disease can be a challenging and complex task, it is best approached in a systematic manner. The guidelines for performing an examination, orienting the images, and the sequential segmental approach provide a framework that can support the understanding of any cardiovascular malformation. It should be reemphasized that the order of images obtained during an examination will not correspond exactly to the segments described. For example, because children frequently dislike suprasternal imaging, the superior veins are usually imaged last—even though they should be included in the “beginning” (the venous segment) of any sequential segmental description.
We gratefully acknowledge the generosity of Dr. William D. Edwards in contributing anatomic images and diagrams to better illustrate this chapter. Thank you very much.
Figure 2.25. Relationship of the aorta and pulmonary artery to the ventricular septal defect in double-outlet right ventricle (DORV). These echocardiographic images are of two different patients with DORV. Top left: Subcostal image demonstrates that the pulmonary artery is distant from the interventricular communication. It is supported by a fully developed, circumferential sleeve of infundibular muscle. Top right: Nearly direct relationship of the aorta to the outlet for ventricular septal defect (yellow arrow). The muscular portion of the upper ventricular septum is marked (yellow asterisk). Continuity between the left ventricle and the aorta can be achieved by insertion of a patch from the superior aspect of this muscular ventricular septum to the anterior aspect of the subaortic conus (yellow arrow). Bottom:Subaortic ventricular septal defect with double outlet from the right ventricle but with a greater length separating the left ventricle from the aortic annulus (white arrow, bottom right image). Bottom left: Completely intact anterior ventricular septum (red asterisk), with both great arteries completely committed to the right ventricular outflow tract, and the side-by-side orientation of the great arteries (aorta to the right). Although this patient can also have patch redirection of left ventricular outflow to the aorta, the likelihood of postoperative subaortic stenosis is greater. A or Ao, aorta; L, left; LV, left ventricle; P or PA, pulmonary artery; RA, right atrium; RV, right ventricle; S, superior.
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1. Lai WW, Geva T, Shirali GS, et al. Task Force of the Pediatric Council of the American Society of Echocardiography. Guidelines and standards for performance of a pediatric echocardiogram: a report from the Task Force of the Pediatric Council of the American Society of Echocardiography. J Am Soc Echocardiogr. 2006;19(12):1413–1430.
2. Oh JK, Seward JB, Tajik AJ. The echo manual. 3rd ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2006.
1.The conceptual approach used to create a complete description of the cardiovascular system is referred to as:
A.the sequential segmental approach.
B.the inflow/outflow approach.
C.the tomographic approach.
D.the anatomic approach.
2.When using an anatomic approach to echocardiographic image orientation, the apical four-chamber view is displayed:
A.with the apex up and the left side of the heart to the examiner’s left.
B.with the apex down and the left side of the heart to the examiner’s left.
C.with the apex up and the left side of the heart to the examiner’s right.
D.with the apex down and the left side of the heart to the examiner’s right.
3.Visceral situs inversus is characterized by which of the following anatomic arrangements of the abdominal organs:
A.Liver and cecum to the right, stomach and spleen to the left
B.Liver and cecum to the left, stomach and spleen to the right
C.Liver in the midline, stomach and spleen to the right
D.Liver in the midline, stomach to the left, and absence of the spleen
4.Cardiac orientation refers to:
A.the position (rightward or leftward) of the heart within the mediastinum.
B.the position (rightward or leftward) of the morphologically right atrium relative to the spine.
C.the orientation of the base to apex axis of the heart (rightward, leftward, or midline).
D.the orientation of the atrioventricular valve insertions into the septum.
5.Straddling occurs when:
A.the chordae of an atrioventricular valve cross a VSD and have their myocardial attachments within the opposite ventricle.
B.the anulus of an atrioventricular valve overrides the ventricular septum in the presence of a VSD.
C.the anulus of a semilunar valve overrides the ventricular septum in the presence of a VSD.
D.a common atrioventricular valve anulus is unequally divided between the two ventricular inlets.
6.Interruption of the inferior vena cava is usually associated with which syndrome?
7.The asymmetrical arrangement of the internal cardiac crux (atrioventricular valve septal attachments) is useful for determining:
A.ventricular to arterial connection.
8.A morphologically right ventricle has which of the following anatomic features:
A.Fine apical trabeculations
B.An atrioventricular valve with septal insertion closer to the cardiac base
C.A moderator band
D.A connection to the pulmonary valve and artery
9.Which of the following atrioventicular connections cannot be used to describe a biventricular heart?
D.Atrioventricular discordance with straddling
10.Which of the following is a term used to describe cardiac orientation?
1.Answer: A. The concept describes the system used to outline each cardiovascular segment (anatomically and functionally) and the connections between these segments in a stepwise progression. It allows a reproducible and complete description of even the most complex malformations. The inflow/outflow approach is a pathologic method of cardiac dissection. The tomographic and anatomic approaches are more related to image orientation than to anatomic description.
2.Answer: D. This orientation displays the image in a manner similar to how the heart would be positioned in a patient who is standing or seated in front of the examiner, allowing for more rapid recognition of spatial anomalies.
3.Answer: B. Option A describes the abdominal organ positions of situs solitus (normal), while options C and D describe anatomy associated with ambiguous situs, as is often seen in heterotaxy syndromes.
4.Answer: C. Orientation refers to the base to apex axis of the heart. Option A is the definition of cardiac position and is determined solely by the location of the heart within the chest, and has no relationship to the internal arrangement of the cardiac structures. Options B and D do not relate to the concept of cardiac orientation.
5.Answer: A. Straddling refers to situations in which some of the chordal supports are anchored within the contralateral ventricle (the ventricle to which the AV valve is not committed). Option B describes anular override, which is not straddling, although the two can coexist in AV valves. Option C describes semilunar valve annulus override and is incorrect because semilunar valves cannot straddle, given the absence of chordae in these valves. Option D is incorrect because a common AV valve cannot straddle since is it by definition committed to both ventricles and therefore should normally have chordal supports within both ventricular cavities.
6.Answer: D. Turner Syndrome is associated with aortic coarctation; Down Syndrome with atrioventricular septal defects and other ventricular septal defects; and Williams Syndrome with supravalvar aortic stenosis.
7.Answer: B. Since the AV valves are formed by delamination from the ventricular endocardial lining, they are intimately and reproducibly associated with their ventricle of origin. Therefore, the asymmetry of the internal crux (apical tricuspid insertion and basal mitral insertion) can be used to designate ventricular morphology as well. The ventricle with an apically inserting AV valve is always a morphologically right ventricle. Options A, C and D are not embryologically related to the AV valves and therefore the internal crux is not helpful in determining their assignments.
8.Answer: C. Options A and B describe features of a morphologically left ventricle. Connection to the pulmonary circulation can occur from either a morphologically right or left ventricle, and therefore is not helpful in assigning ventricular morphology.
9.Answer: A. The other three responses are all possible in both biventricular or univentricular AV connections. However, when there is only a single inlet, the heart can only achieve a functionally single ventricular circulation.
10.Answer: B. Levocardia describes the base to axis orientation of the heart. Levocardia is the normal cardiac orientation with the apex pointed leftward (mesocardia refers to a midline apex, dextrocardia to a rightward pointed apex). Levo-, meso-, and dextroposition refer to the location of the cardiac mass within the chest.