d-Transposition of the great arteries (d-TGA) is one of the two most common forms of cyanotic congenital heart disease, with tetralogy of Fallot having comparable incidence. In population-based series, the incidence of d-TGA is 20 to 22 per 100,000 live births. Typically, neonates with d-TGA present in the first day or two of life with cyanosis without significant respiratory distress. Frequently no cardiac murmur is present, particularly in the absence of a ventricular septal defect (VSD). The electrocardiogram and chest radiograph are frequently normal. If a VSD or outflow tract obstruction is present, a murmur characteristic of these associated lesions may be present.
Maintenance of a compensated clinical state is dependent on adequate mixing between the pulmonary and systemic circuits. Neonates with an intact atrial septum or very restrictive patent foramen ovale can present with profound cyanosis and findings consistent with low cardiac output in the delivery room. Those whose intercirculatory mixing is initially augmented by a patent ductus arteriosus (PDA) can develop worsening cyanosis and low cardiac output as the ductus constricts. Uncommonly, neonates with d-TGA who have good intercirculatory mixing escape notice in the first few days of life and may present later with signs of heart failure, typically accompanied by a murmur originating from either excessive flow across the left ventricular outflow tract or across a VSD.
Diagnosis by fetal echocardiography is another mode of presentation, generally prompted by abnormal findings on a routine obstetric screening ultrasound. Prenatal detection of d-TGA by echocardiography requires examination of the outflow tracts, because examining only the number and size of cardiac chambers will not detect this anomaly (Figs. 16.1 to 16.4; Video 16.1). The frequency of antenatal diagnosis of d-TGA varies considerably, ranging from 20%–50% in recent publications.
ANATOMY AND PHYSIOLOGY
In d-TGA, the atrial situs, atrioventricular alignments, and ventricular looping are all normal. TGA is present, meaning that the aorta arises from the right ventricle while the pulmonary artery arises from the left ventricle (Fig. 16.5). The designation d- refers to the relative positions of the aortic and pulmonary valves; d- (dextro-) indicates that the aortic valve is rightward of (and typically anterior to) the pulmonary valve, in accordance with the convention established by Van Praagh. There may be other associated malformations, most commonly the presence of a VSD, which occurs in approximately 35% to 40% of cases and can be of various anatomical types.
Figure 16.1. Fetal echocardiogram performed at 20 weeks’ gestation. Imaging from the four-chamber view (arrow), directed anteriorly, demonstrates the parallel nature of the great arteries. The great vessels appear symmetrical with a large outlet ventricular septal defect positioned directly below the semilunar valves. Ao, aorta; PA, pulmonary artery.
Figure 16.2. Fetal d-transposition of the great arteries (d-TGA) at 20 weeks’ gestation demonstrates a well-developed pulmonary artery arising posteriorly from the left ventricular chamber (arrow). The patent ductus arteriosus is directed posteriorly toward the spine, and the right pulmonary artery branch is also seen. LV, left ventricle; PDA, patent ductus arteriosus; MPA, main pulmonary artery; RPA, right pulmonary artery.
Figure 16.3. Scanning anteriorly in this fetus at 20 weeks gestation, the anterior aorta is seen to arise from the right ventricle (arrow). Two head-and-neck vessels are seen originating from the transverse aortic arch, confirming this as the true aortic arch. A ventricular septal defect is noted in the region of the outlet septum. RV, right ventricle; LV, left ventricle.
The physiologic consequence of these anatomic relationships is that two parallel circulations are established. Systemic venous blood returns to the right atrium and from there passes to the right ventricle and aorta and back to the systemic arterial bed without being oxygenated. Pulmonary venous blood returns to the left atrium and thereafter passes to the left ventricle, pulmonary artery, and pulmonary arterial bed without any opportunity to deliver its oxygen cargo. This arrangement is only compatible with life if some intercirculatory mixing (bidirectional shunting) is present. Mixing can occur via an interatrial communication (patent foramen ovale or true atrial septal defect), VSD, or PDA, but is most effective across an atrial septal defect.
Figure 16.4. Short-axis view of the semilunar valves in a fetus with d-TGA. The aortic valve is seen to be trileaflet and positioned anterior (arrows) and rightward relative to the pulmonary valve. AoV, aortic valve; PV, pulmonary vein.
Figure 16.5. Schematic diagram of d-transposition of the great arteries (d-TGA). (From Lippincott’s Nursing Advisor 2012. See: www.LippincottSolutions.com )
The preferred operative approach in the current era for management of d-TGA is the arterial switch operation (ASO). Thus, any anatomical feature that makes performing an ASO difficult or impossible is important for the echocardiographer to identify. In this operation, both great vessels are transected, the branch pulmonary arteries are brought anterior to the neoaortic root (LeCompte maneuver), the coronary arteries are transferred from the native aortic root to the neoaortic root, and the great vessels are reanastomosed in the “switched” position (Fig. 16.6). Any significant atrial or ventricular septal defect is closed. Obstruction of either outflow tract, abnormalities of the pulmonary valve (which would function as the neoaortic valve after ASO), certain coronary patterns, nonfacing sinuses of the semilunar valves, and straddling of the tricuspid valve through a VSD (Video 16.4) are examples of such anatomical features that may complicate an ASO. Multiple muscular VSDs may be difficult to close and thus affect the management strategy. Aortic arch obstruction, while uncommon, needs to be identified so that it can be appropriately addressed at surgery.
Late clinical presentations of d-TGA raise additional concerns. First, if the left ventricular systolic pressure is low, concern is raised about the ability of the left ventricle to handle an acute transition to the pressure load of the systemic circulation. However, echocardiographic parameters of left ventricular shape or mass have not been shown to predict outcome after a late arterial switch, although extrapolated parameters have been used in surgical decision making. Second, pulmonary vascular disease is known to develop at an accelerated rate in patients with d-TGA and should be a consideration in patients over several months of age.
Figure 16.6. Surgical technique of the arterial switch operation. A: The ductus arteriosus is divided between suture ligatures and the branch pulmonary arteries are dissected out to the hilum to provide adequate mobility for anterior translocation. B: Transection of the great arteries. The left ventricular outflow tract, neoaortic valve, and coronary arteries are thoroughly inspected. C: The coronary arterial buttons are excised from the free edge of the aorta to the base of the sinus of Valsalva. D: The coronary buttons are anastomosed to V-shaped excisions made in the aorta. E: The pulmonary artery is brought anterior to the aorta (LeCompte maneuver). Anastomosis of the proximal neoaorta is shown. F: The coronary donor sites are filled with autologous pericardial patches. Two separate patches (F) or a single U-shaped patch (G) may be used. G: Anastomosis of the proximal neopulmonary artery and distal pulmonary artery. H: Completed anastomosis of the proximal neopulmonary artery and the distal pulmonary artery. (Reprinted from Wernovsky G. Transposition of the great arteries. In: Allen HD, Driscoll DJ, Shaddy RE, et al, eds. Moss and Adams’ Heart Disease in Infants, Children, and Adolescents. 7th ed. Philadelphia: Lippincott Williams & Wilkins; 2008:1038–1087, with permission. Permission also obtained from the original source: Sabiston DC Jr, Spencer FC, eds. Surgery of the Chest. Philadelphia: WB Saunders; 1990:1435–1446.)
The echocardiographer has an important role in evaluating patients who have previously undergone surgery for d-TGA. The ASO became the predominant surgical strategy at most institutions by the late 1980s, and thus the longest published longitudinal follow-up data available are 15 to 20 years after ASO. As such data emerge, it has become apparent that important postoperative issues include coronary occlusion (symptomatic or asymptomatic) in 3% to 14% of patients, stenosis at the great vessel anastomoses (supravalvar pulmonic stenosis being more common than supravalvar aortic stenosis [5% to 30% versus 2% to 5%]), neoaortic root dilation in about 50%, neoaortic insufficiency (trivial to mild, about 30%; moderate to severe, 1% to 7%), and uncommonly, clinically significant bronchopulmonary collateral vessels. Rarely, patients who underwent ASO in the neonatal period present later with pulmonary arterial hypertension; the etiology of this phenomenon remains unclear.
Before the ASO era, patients were managed with an atrial level “switch,” using either the Senning or Mustard technique. These two techniques involve rerouting systemic venous drainage to the mitral valve and pulmonary venous drainage to the tricuspid valve by way of intra-atrial baffles. The circulation is physiologically “corrected,” but the right ventricle serves as the systemic ventricle while the left ventricle serves as the pulmonary ventricle. Late complications include sinus node dysfunction and other atrial arrhythmias (40% to 60%), baffle obstruction or leak (5% to 31%), right ventricular dysfunction (about 60% at 25-year follow-up), tricuspid regurgitation, and left ventricular outflow tract obstruction.
BASICS OF ECHOCARDIOGRAPHIC ANATOMY AND IMAGING
Classic Two-Dimensional Echocardiographic Anatomy and Hemodynamics
The diagnosis of d-TGA is established by demonstrating normal atrial situs, atrioventricular alignments, and ventricular looping, in association with ventrículoarterial discordance. The aorta arises from the right ventricle, while the pulmonary artery arises from the left ventricle. In most cases, the aortic valve is anterior and to the right of the pulmonary valve, and there is characteristically fibrous continuity between the pulmonary and mitral valve. With this fundamental anatomy established, the sonographer can then proceed to evaluate additional key anatomical features such as the presence or absence of VSD(s), coronary artery pattern, outflow tract and semilunar valve anatomy, and aortic arch anatomy (Video 16.2).
Beginning with a two-dimensional subcostal frontal sweep allows the sonographer to establish atriovisceral situs, atrioventricular alignments, and ventricular looping (Fig. 16.7). As the sweep is extended to the outflow tracts and great vessels, the more posterior semilunar valve arising from the left ventricle is seen to give rise to a great vessel that bifurcates, consistent with the pulmonary artery. The more anterior great vessel arises from the right ventricle and does not bifurcate, consistent with the aorta. This initial sweep also allows the sonographer to glean preliminary information about the size of the interatrial communication and the presence or absence of a VSD. Two-dimensional subcostal short-axis sweeps provide further opportunities to evaluate the atrial and ventricular septa and ventricular morphology and to visualize the parallel orientation of the great vessels (Fig. 16.8). The size of any interatrial communication or VSD should be measured. The coronary arteries may be visualized from various subcostal views. In particular, the subcostal frontal sweep is useful when the circumflex coronary artery arises from the right coronary artery and has a retropulmonary course, which is the second most common coronary artery arrangement in d-TGA (Fig. 16.9; Video 16.3). In this situation, the circumflex is typically well seen due to its perpendicular orientation to the plane of sound. Its position anterior to the mitral annulus but posterior to the pulmonary valve can be established. With proper transducer angulation, a substantial length of circumflex coronary artery can be viewed as a “train track.” Information about coronary arterial anatomy from subcostal views is usually complementary to that from the parasternal short-axis view. Color Doppler evaluation from subcostal views further defines shunting across an interatrial communication or VSD and provides information about atrioventricular and semilunar valve function (Fig. 16.10). Spectral Doppler interrogation of the PFO or ASD (with mean gradient) should be obtained from the subcostal frontal or short-axis view as well as spectral Doppler interrogation of the outflow tracts and semilunar valves.
Figure 16.7. Subcostal four-chamber view. A: Transverse view through the liver demonstrates normal visceral situs with normal position of the inferior vena cava and aorta. IVC, inferior vena cava; Ao, aorta. B: View of the atria demonstrates the atrial situs and the atrial septal defect. In this case, a large communication after balloon atrial septostomy is demonstrated. LA, left atrium; RA, right atrium. C: With continued anterior angulation, the left ventricle is seen to give rise to the pulmonary artery, which bifurcates into the right and left branch pulmonary arteries. PA, pulmonary artery; RA, right atrium; RV, right ventricle; LV, left ventricle. D: With extreme anterior angulation, the right ventricle is seen to give rise to the aorta, which courses superiorly and does not bifurcate. Ao, aorta; LCA, left coronary artery; RA, right atrium; RV, right ventricle.
Figure 16.8. Subcostal short-axis view. A: The right and left atria and the atrial septal defect are well seen. LA, left atrium; RA, right atrium. B: Sweeping toward the apex, the ventricles are seen. The left ventricle has a characteristically smooth septal surface and two mitral valve papillary muscles are seen. A muscular ventricular septal defect is noted. LV, left ventricle; RV, right ventricle. C: The great vessels are seen in parallel with the aorta anterior and arising from the right ventricle. Ao, aorta; PA, pulmonary artery.
For sonographers who start the study from a parasternal long-axis view, the characteristic parallel orientation of the two great vessels is readily apparent (Fig. 16.11), although this view does not provide as ready assessment of the normalcy of other aspects of the anatomy as the subcostal approach does. Pulmonary–mitral valve fibrous continuity is usually present in this view. From the parasternal long-axis view, the aortic and pulmonary annuli should be measured in systole; the pulmonary valve annulus is normally slightly larger than the aortic valve annulus. Any abnormalities of the semilunar valve structure or function should be noted. Outflow tract obstruction or a malalignment-type VSD should be readily apparent. Color Doppler evaluation of all four cardiac valves should be performed.
Figure 16.9. The circumflex coronary artery is well seen in this subcostal four-chamber view. Watching this entire imaging sweep allows one to identify that the circumflex courses posterior to the pulmonary artery. RA, right atrium; LV, left ventricle.
Turning to the parasternal short-axis view, one notes the relative position of the aortic and pulmonary valves (Fig. 16.12). Typically, the aortic valve is anterior and slightly rightward of the pulmonary valve annulus, although the positions can range along a continuum from the aortic valve directly anterior to the pulmonary valve, to side-by-side great vessels (aortic valve rightward) to even an anterior leftward aortic valve position in a minority of cases. Any structural abnormality of the aortic or pulmonary valve should be noted. The intercoronary commissure of the aortic valve is most commonly directly aligned with a commissure of the pulmonary valve (Fig 16.12A). If this is not the case (Fig 16.12B), this finding should be communicated to the surgeon as it may complicate the coronary transfer.
The parasternal short-axis view is also the primary view from which the coronary arterial pattern is determined. This information is of paramount importance for surgical planning as certain coronary artery patterns may add significantly to the technical difficulty of the operation (see also “Key Findings that Alter Management” later). Several nomenclature schemes have been developed to describe coronary artery patterns in d-TGA; the most commonly used nomenclatures are the Leiden convention (Table 16.1) and the descriptive approach popularized by Boston Children’s Hospital (Table 16.2, Fig. 16.13). Yacoub and Radley-Smith also developed a nomenclature scheme in the 1970s (Types A through F), but this scheme is not comprehensive and is not further described in this text. The most common coronary artery patterns are shown in Figures 16.13, 16.14, and 16.15 (Videos 16.2, 16.3, 16.5). Table 16.3gives the relative frequencies of the most common coronary patterns. If coronary arterial anatomy is difficult to resolve, moving up one or two interspaces from the usual parasternal short-axis view (“high parasternal” view) may be helpful. The parasternal long-axis view, apical view, and subcostal views often add valuable complementary information (Figs. 16.9 and 16.16). Color Doppler with a low Nyquist value (usually 15–30 cm/s) should be used to confirm the appropriate direction of flow within structures thought to be the coronary arteries.
Figure 16.10. Subcostal views with the addition of color Doppler. A: Color flow Doppler across the atrial septal defect from the subcostal four-chamber view demonstrates the direction of shunting, which at this moment in time is left to right. LA, left atrium; RA, right atrium. B: Spectral Doppler interrogation of the atrial septal defect demonstrates low-velocity, bidirectional shunting. C: Color flow Doppler across the ventricular septum from the subcostal short-axis view demonstrates a small muscular ventricular septal defect. VSD, ventricular septal defect; RV, right ventricle; LV, left ventricle.
Figure 16.11. Parasternal long-axis view. A: The great vessels are seen in parallel. RV, right ventricle; Ao, aorta; LV, left ventricle; LA, left atrium; PA, pulmonary artery;. B: The pulmonary valve annulus measures 7 mm (green pluses). LV, left ventricle; LA, left atrium; PA, pulmonary artery. C: The aortic valve annulus (6 mm) (green pluses) is normally slightly smaller than the pulmonary valve annulus. RV, right ventricle; Ao, aorta.
Figure 16.12. Parasternal short-axis view. A: Typical relative positions of the aortic and pulmonary valves, with the aortic valve anterior and slightly rightward. Note that the facing commissures of the two valves are aligned. AoV, aortic valve; PV, pulmonary vein. B: In this patient, the commissures of the semilunar valves are not aligned. AoV, aortic valve; PV, pulmonary vein.
A careful inspection of the ventricular septum for VSD(s) with two-dimensional imaging is also performed in the parasternal short-axis view (Fig. 16.17). If a VSD is present, its anatomical type is determined. Color Doppler interrogation of the ventricular septum confirms the presence or absence of VSD(s) as well as the direction of flow, which is frequently bidirectional in the neonate with d-TGA. Since right and left ventricular systolic pressures will be very similar in the neonate, using low Nyquist limits (60 cm/s or lower) will help detect low-velocity ventricular-level shunts. If a VSD is present, spectral Doppler interrogation of the VSD jet allows estimation of the transventricular pressure gradient.
The apical views are most useful in d-TGA for assessing valvar function and ensuring normal ventricular sizes (Fig. 16.18). The great vessel arising from the left ventricle can be visualized to bifurcate, demonstrating that it is the pulmonary artery. The structure and function of the atrioventricular and semilunar valves are assessed with two-dimensional, color Doppler, and spectral Doppler imaging. The apical view can also add some confirmatory information about coronary artery anatomy, particularly in the coronary variant in which the circumflex coronary artery arises from the right coronary artery and passes posterior to the pulmonary root. This course of the circumflex coronary artery can be seen on an apical sweep from posterior to anterior.
Long-axis suprasternal notch imaging provides the best view of the ductus arteriosus to assess its patency and size by two-dimensional imaging (Fig. 16.19). In addition, the aortic arch should be carefully inspected to rule out transverse arch hypoplasia or coarctation. Color flow Doppler demonstrates the direction of ductal flow as well as flow through the aortic arch. Pulsed-wave spectral Doppler interrogation within the ductus arteriosus further clarifies the pattern of shunting, which is typically predominantly from the aorta to the pulmonary artery. Short-axis suprasternal notch imaging may be useful in clarifying coronary artery anatomy as well.
Basic Imaging of d-TGA—Challenges
Generally, identification of d-TGA is straightforward for any sonographer who has at least some experience with congenital heart disease. Delineation of the coronary artery anatomy is much more challenging, given the small size and quite anterior location of the coronary arteries. Higher-frequency transducers with lower dynamic range settings may make the coronary arteries easier to visualize. At times, one sees linear, echo-free spaces in the vicinity of the semilunar valves, which are easily confused with the true coronary arteries. Confirmation that a structure truly represents a coronary artery can be made by demonstrating color Doppler flow with appropriate direction within the space and acquiring confirmatory images from other views. Coronary arteries that arise higher than usual (at the sinotubular junction or above) will be difficult to visualize in the expected parasternal short-axis view, but may be identified by sweeping more cranially in the parasternal short-axis view or from the parasternal long-axis view (Fig. 16.20).
Ventricular septal defects, particularly small muscular ventricular septal defects, can be easily overlooked when ventricular pressures are equal, particularly in the presence of large patent ductus arteriosus or additional large ventricular septal defect. Careful inspection of the 2D images of the ventricular septum and color flow assessment of the entire muscular septum are necessary (see Figs. 16.8B, 16.17).
Figure 16.13. Coronary artery patterns in d-transposition of the great arteries (d-TGA). Nomenclature for each pattern (Children’s Hospital Boston and Leiden conventions) is given in each set of images. Top: Diagnostic projection; diagram of the origin and proximal course as visualized by two-dimensional echocardiography and caudally angulated aortography. Bottom: Same coronary artery distribution as viewed anteriorly (surgeon’s view, frontal projection). Note that the circumflex coronary artery, or even the entire left coronary artery system, is more likely to pursue a retropulmonary course when the great arteries are in a side-by-side relationship. (Reprinted from Wernovsky G. Transposition of the great arteries. In: Allen HD, Driscoll DJ, Shaddy RE, et al, eds. Moss and Adams’ Heart Disease in Infants, Children, and Adolescents. 8th ed. Philadelphia: Lippincott Williams & Wilkins; 2012:1097–1046, with permission. Permission also obtained from the original source: Wernovsky G, Sanders SP. Coronary artery anatomy and transposition of the great arteries. Coron Artery Dis. 1993;4:148–157.)
Figure 16.14. Two-dimensional parasternal short-axis views of the most common coronary artery pattern, termed “usual” or by the Leiden classification [1 AD, Cx; 2 R]. A: The origin of the left coronary artery is from the leftward sinus that is adjacent to or “facing” the pulmonary valve. Slight angulation away from a standard parasternal short-axis view may be necessary to demonstrate the origin of the vessel. Ao, aorta; PA, pulmonary artery. B: The bifurcation of the left coronary artery cannot be demonstrated in the same still frame as the origin but is well seen here. Ao, aorta; PA, pulmonary artery; left anterior descending coronary artery. C: The origin of the right coronary artery is from the rightward sinus that is “facing” the pulmonary valve. Ao, aorta; PA, pulmonary artery; RCA, right coronary artery.
Assessment of the degree of outflow tract obstruction or semilunar valve stenosis is critical to surgical management decisions. However, Doppler assessment of the severity of obstruction may be misleading. In the presence of a large PDA, great vessel pressures are equalized and the Doppler interrogation of either the outflow tracts or semilunar valves may underestimate the amount of obstruction present. In an older infant or child whose pulmonary vascular resistance has fallen and who has effective intercirculatory mixing (with pulmonary blood flow significantly greater than systemic blood flow), the degree of left ventricular outflow tract obstruction or pulmonary valve stenosis may be overestimated by the Doppler gradient. In either instance, careful two-dimensional imaging can add valuable information about the degree of obstruction.
COMMON ASSOCIATED LESIONS AND FINDINGS
Key Findings That Alter Clinical Management
The basic approach to the management of d-TGA includes consideration of balloon atrial septostomy, depending on the effectiveness of mixing, followed by surgical intervention. The current era of cardiovascular surgery entails the performance of the arterial switch procedure. In the past era (pre-1980), the surgery of choice was the atrial switch (Senning or Mustard), but these procedures fell out of favor due to the nonphysiologic nature of the operation as well as the high risk of development of late atrial arrhythmias and progressive right (systemic) ventricular dysfunction. As with all cardiac malformations, center-to-center variability exists regarding alterations in management based on variations in cardiac anatomy. The following represents a range of management approaches that might be considered when a specific associated anomaly is detected that alters the basic underlying anatomy (Table 16.4):
1. Restrictive patent foramen ovale. Most centers use balloon atrial septostomy in the majority of cases of d-TGA. During the initial baseline transthoracic echocardiogram, the identification of a restrictive atrial communication prompts performance of a septostomy. Restriction of the atrial septum is echocardiographically determined by 2D imaging of a small foraminal flap; color and spectral Doppler provide supportive information. Clinically, the neonate will manifest reduced oxygen saturation as an indicator of inadequate mixing across the atrial septum. In contrast, a sufficient native ASD or large VSD in the presence of a well-saturated neonate may prompt the care team to decide against balloon septostomy and to proceed directly to surgery. The septostomy is typically performed with echocardiographic guidance (Figs. 16.21 and 16.22). Imaging is performed via an apical or a subcostal window, with interaction occurring between the interventional cardiologist and echocardiographer such that identification of balloon position as well as adequacy of the newly created atrial communication may be discussed.
2. Muscular ventricular septal defect. It is common to identify a perimembranous or malalignment VSD in the setting of d-TGA. However, occasionally a mid-muscular or apical VSD is identified. If the VSD is deemed to be of hemodynamic significance, the surgical approach is usually to attempt primary closure at the time of the arterial switch. Some of these VSDs may be inaccessible to the surgeon. In the neonate, this would prompt alternative management strategies such as pulmonary artery band placement. If, at the time of band removal, the VSD is considered to be hemodynamically important, then concomitant performance of either a percutaneous VSD device implantation or surgical closure can be considered.
3. Pulmonary valve stenosis or subpulmonic stenosis. In the presence of pulmonary outflow tract obstruction (Fig 16.23), a number of surgical approaches can be considered. An arterial switch can be performed if the valve stenosis is mild or deemed amenable to repair and the semilunar valves are of similar size. Resection of subpulmonic conal tissue can also be considered, although residual left ventricular outflow tract narrowing may lead to systemic obstruction after the arterial switch. If these modifications to the arterial switch are considered to be of unacceptable risk and a large VSD is present, then a Rastelli-type repair can be considered with closure of the VSD to the aorta and placement of a right ventricle–to–pulmonary artery conduit. More recently, the Nikaidoh procedure has been developed, which involves enlargement of the VSD, translocation of the aorta posteriorly, closure of the VSD, and reconstruction of the right ventricular outflow tract to the pulmonary artery. If there is no VSD, then choices would include atrial switch with left ventricle–to–pulmonary artery conduit or a single-ventricle palliation.
4. Aortic valve stenosis or subaortic stenosis. Right ventricular outflow tract obstruction is commonly found in association with an anterior malaligned VSD. If not severe, this anatomical variant is better tolerated than obstruction to pulmonary outflow in that the arterial switch will result in postoperative neopulmonary obstruction. Depending on the severity and extent of RVOT obstruction, this lesion can be palliated via valve repair, subvalvar muscular resection, transannular patch, or pulmonary conduit placement.
5. Coarctation of the aorta. Coarctation of the aorta is an uncommon association with otherwise straightforward d-TGA. However, it may be difficult to identify early after birth in that these children are frequently receiving prostaglandin E1 and a large patent ductus arteriosus is present. At the initial echocardiographic evaluation, secondary features may suggest the possibility of underlying aortic arch obstruction. These findings may include (a) a bicuspid aortic valve, (b) an anterior malalignment VSD, (c) two-dimensional appearance of arch hypoplasia, (d) presence of a posterior shelf, (e) an abnormally extended distance from the left common carotid to the left subclavian artery (typically greater than 1 cm), (f) blunted antegrade flow in the descending aorta with diastolic runoff, or (g) predominantly right-to-left ductal shunting. In those neonates where prostaglandin is stopped and the ductus arteriosus is allowed to close before the arterial switch, aortic arch obstruction should be unmasked. If a coarctation is identified, this is typically repaired at the time of the arterial switch.
6. Coronary artery anomaly. Coronary anatomy variants were reviewed earlier in this chapter. These variations are virtually always identified by echocardiographic assessment, but occasionally cardiac catheterization may be necessary. The two most common patterns, “usual” and circumflex from the right coronary artery, are readily “switchable.” There are several articles and textbook chapters stating unequivocally that there are no “unswitchable” coronary artery patterns. That being said, a single coronary from either the nonfacing (anterior) sinus or even the left- or right-facing sinuses if arising anteriorly within that sinus has been described to have very high operative risk for an ASO. Other patterns that carry higher surgical risk include intramural coronary arteries. In these situations, alternate surgical strategies may be considered, including the Damus-Kaye-Stansel procedure, which does not require coronary reimplantation.
7. Late diagnosis or complications that delay surgery. Delay in the diagnosis of d-TGA beyond several weeks of life or the presence of noncardiac conditions (e.g., prematurity, infection, noncardiac organ dysfunction) may preclude a timely arterial switch procedure. There has been significant debate as to the appropriate management of such patients, with the possible strategies including primary delayed ASO, two-stage ASO (initial pulmonary artery band, frequently accompanied by an aortopulmonary shunt to maintain adequate oxygen saturations, followed at some time interval by ASO), or for extremely delayed presentations, an atrial level switch. This debate typically arises in the neonate without a VSD of adequate size to maintain systemic left ventricular pressure. Although echo parameters have been proposed to assess both perceived risk for ASO and hypertrophic response to pulmonary artery banding, these parameters have not been shown to be predictive of outcome. In fact, Foran and colleagues showed no relationship between preoperative left ventricular geometry by echo and outcome after delayed primary ASO. Application of standard formulae for calculation of LV mass is problematic due to the crescentic shape of the LV.
Figure 16.15. Parasternal short-axis imaging of the second most common coronary pattern, termed “circumflex from the right” or by the Leiden classification [1 AD; 2 R, Cx]. The left coronary artery arises from the left anterior facing sinus and gives rise only to the left anterior descending coronary artery. The right coronary artery arises from the right posterior facing sinus and gives rise to the right and circumflex coronary arteries. The circumflex courses posterior to the pulmonary root. A: The origin of the left coronary artery is seen. AoV, aortic valve; LCA, left coronary artery; PV, pulmonary vein. B: The origin of the right coronary artery is seen. AoV, aortic valve; RCA, right coronary artery; PV, pulmonary vein. C: Color confirmation of the origin of the right coronary artery. Note the low Nyquist limit necessary to visualize color flow in this structure. AoV, aortic valve; RCA, right coronary artery. D: Two-dimensional and color flow imaging of the right coronary artery coursing toward the right atrioventricular groove. AoV, aortic valve; RCA, right coronary artery. E: Color flow imaging of the circumflex coronary artery coursing posterior along the pulmonary root. AoV, aortic valve.
Figure 16.16. Supplemental coronary views from alternative windows in a patient with the coronary pattern of circumflex from the right coronary artery. See also Figure 16.9. A: Parasternal long-axis view of the circumflex coronary artery. Its posterior position relative to the pulmonary root is apparent when sweeping through the heart. RV, right ventricle; IVS, interventricular septum; LV, left ventricle; LA, left atrium. B: Apical four-chamber view demonstrating the course of the circumflex coronary artery; anteroposterior sweeps demonstrate that it runs posterior to the pulmonary root. LA, left atrium; RA, right atrium; LV, left ventricle; RV, right ventricle.
Figure 16.17. Parasternal short-axis views demonstrating a large posterior muscular ventricular septal defect in d-TGA. A: Two-dimensional imaging. RV, right ventricle; LV, left ventricle. B: Color flow imaging showing right ventricle–to–left ventricle shunting. C:Spectral Doppler display confirming low-velocity, right ventricle–to–left ventricle shunting. RV, right ventricle; LV, left ventricle.
Figure 16.18. Apical views. A: Apical four-chamber view in this patient who previously had a balloon atrial septostomy. The four-chamber view shows normal cardiac chamber morphology and size. ASD, atrial septal defect; RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle. B:Anterior angulation from the apical four-chamber view demonstrates the pulmonary artery arising from the left ventricle. RPA, right pulmonary artery; LPA, left pulmonary Artery; MPA, main pulmonary artery.
Figure 16.19. The patent ductus arteriosus is best visualized from the suprasternal long-axis view in d-TGA. A: Two-dimensional imaging. Ao, aorta; PDA, patent ductus arteriosus; LPA, left pulmonary Artery. B: Color flow imaging in systole demonstrating pulmonary artery–to–aorta shunting. Ao, aorta; PDA, patent ductus arteriosus; LPA, left pulmonary Artery. C: Color flow imaging in diastole demonstrating aorta–to–pulmonary artery shunting. Ao, aorta; PDA, patent ductus arteriosus; LPA, left pulmonary Artery. D: Spectral Doppler display showing the typical bidirectional shunting pattern in a neonate with d-TGA and a patent ductus arteriosus.
Figure 16.20. High arising left coronary artery. A: From the parasternal short-axis view, a normal right coronary origin is seen. A portion of the left coronary artery, although not its origin, is also visualized. Note that the aortic valve leaflets are easily seen in this frame. AoV, aortic valve; RCA, right coronary artery; LCA, left coronary artery. B: With more cranial angulation in the parasternal short-axis view, the left coronary origin is visualized. Note that the aortic valve leaflets are no longer seen in this plane. Ao, aorta; PA, pulmonary artery. C: From a subcostal frontal view, anteriorly angulated to the aortic outflow, the origin of the left coronary artery can be seen arising above the sinotubular junction. This observation is confirmed by color flow Doppler. LCA, left coronary artery; Ao, aorta.
INTERVENTIONAL AND POSTINTERVENTIONAL IMAGING
Preoperative Cardiac Catheterization
In the neonate with unoperated d-TGA, the most common use of transthoracic echocardiography in conjunction with cardiac catheterization involves the performance of a balloon atrial septostomy. The use of transthoracic imaging is crucial regardless of where the interventionalist is performing the procedure (i.e., at the bedside or in the catheterization laboratory). After balloon inflation an evaluation is made of balloon position within the left atrium, ensuring it is away from the pulmonary veins and mitral valve apparatus. After septostomy, the anatomy of the newly created atrial communication is assessed, and restriction to flow is determined by color and pulsed-wave Doppler. The infant will typically manifest a prompt improvement in oxygen saturation such that prostaglandin can be weaned off.
Angiography may infrequently be required to delineate the coronary arteries if transthoracic echocardiography is unable to define the pattern completely. The need for this level of definition is surgeon specific, but the lack of identification of specific high-risk patterns has been associated with less-optimal surgical outcomes.
Figure 16.21. Subcostal long-axis view of the right and left atria with imaging performed during bedside balloon atrial septostomy. Echocardiographic guidance ensures optimal catheter and balloon position prior to the performance of the septostomy. The balloon is positioned against the atrial septum prior to the procedure, away from the pulmonary veins and mitral valve apparatus. RA, right atrium.
Figure 16.22. Subcostal long-axis imaging after balloon atrial septostomy confirms lack of restriction across a widely patent foramen flap. This should be accompanied by a prompt improvement in oxygen saturation. LA, left atrium; RA, right atrium.
Figure 16.23. d-Transposition of the great arteries, posterior malalignment VSD, and subpulmonic stenosis. A: Parasternal long-axis two-dimensional imaging demonstrating the posteriorly malaligned conal septum (arrow) creating subpulmonic obstruction. VSD, ventricular septal defect; PV, pulmonary vein; LV, left ventricle. B: Subcostal frontal color imaging demonstrating subpulmonic obstruction with aliasing of flow by color Doppler. PA, pulmonary artery; RV, right ventricle; LV, left ventricle.
Many pediatric centers currently use transesophageal echocardiography (TEE) for all cases of d-TGA repair. Preoperative imaging typically entails a complete reassessment of anatomy and physiology. This includes evaluation of the great artery relationships, VSD(s), atrial communication (native or created), valve anatomy and function, coronary artery anatomy, outflow tract obstruction, systemic and pulmonary venous anatomy, and ventricular chamber dimensions and contractility. The arterial switch operation entails division of the ductus arteriosus, transection of both great vessels, closure of any atrial or ventricular septal defect, repositioning of the branch pulmonary arteries anterior to the ascending aorta (“LeCompte maneuver”), transfer of coronary buttons from the native aortic root to the “neoaortic” (native pulmonic) root, and re-anastomosis of both great vessels in their new positions. Postoperative assessment begins during warming to assess for myocardial or intracardiac cavitations consistent with air. After separation from cardiopulmonary bypass, a thorough evaluation is undertaken to ensure that the repair is acceptable. After the arterial switch procedure, the following are important components of the examination: (a) demonstrate resolution of atrial, ventricular, and ductal shunts, (b) demonstrate flow into the reimplanted coronary arteries, (c) document relief or development of outflow tract obstruction, (d) assess valve function, (e) rule out supravalvar aortic or pulmonary stenosis at the anastomotic sites, (f) estimate pulmonary artery pressures, (g) evaluate ventricular contractility, (h) assess bilateral branch pulmonary artery anatomy and flow by two-dimensional imaging, color and pulsed-wave Doppler interrogation, and (i) secondary confirmation of bilateral branch pulmonary artery flow by demonstration of left- and right-sided pulmonary venous return.
Postoperative Imaging: Arterial Switch Operation
Postoperative transthoracic echocardiography should encompass all the elements listed above under intraoperative imaging. In particular, the supravalvar pulmonary artery anastomosis is readily evaluated from either a parasternal short-axis imaging plane or a subcostal short-axis view (Fig. 16.24, Video 16.6). After the LeCompte maneuver, there is the potential for branch pulmonary artery stenosis. Postoperative two-dimensional, color and spectral Doppler evaluation of the pulmonary artery branches as they straddle the aorta can be readily accomplished from the high parasternal short-axis imaging plane (Fig. 16.25). Commonly, a mild degree of flow acceleration (≤2.5 m/s) is observed, which is generally not problematic.
The coronary arteries are typically imaged from the parasternal short-axis window, facilitated by color Doppler imaging (Fig 16.26). Spectral Doppler interrogation can be used if aliased color flow is noted at low Nyquist limits. In the case of poor postoperative windows or in the older patient, the coronary arteries may be difficult or impossible to visualize. While echocardiographic assessment may suggest kinking or abnormally accelerated flow within a coronary artery, echocardiography rarely, if ever, is of acceptable precision for the surgeon to consider repair on these noninvasive data alone (Figs. 16.26C,D). Angiography is usually prompted by disturbing echocardiographic findings (Fig 16.26E).
Figure 16.24. Parasternal short-axis view demonstrates narrowing at the supravalvar pulmonary artery anastomotic site after the arterial switch procedure (arrows). Color Doppler interrogation defines the site of obstruction, located distal to the valve leaflets. Ao, aorta.
Progressive aortic root dilation is well described after the arterial switch procedure with concern for late development of significant aortic insufficiency (Fig 16.27). Significant degrees of aortic stenosis and insufficiency are uncommon at mid-term follow-up. Marino and colleagues reported a 3.7% incidence of significant aortic insufficiency at a median of 8.8 years of follow-up, but noted that 46% of their subjects with aortic insufficiency had progressed at least one grade of insufficiency since the initial postoperative echocardiogram. Aortic dilation has been associated with d-TGA with a VSD as opposed to those with an intact ventricular septum.
Figure 16.25. Anatomy of the branch pulmonary arteries status post arterial switch procedure with Lecompte maneuver. The branch pulmonary arteries straddle the aortic root. A: High parasternal short-axis view with color Doppler (arrows). RPA, right pulmonary artery; LPA, left pulmonary artery. B: CT angiogram showing the branch pulmonary arteries as they straddle the ascending aorta. AAO, ascending aorta; LPA, left pulmonary Artery; RPA, right pulmonary artery. C: 3D reconstruction of a patient’s CTA angiogram, illustrating the Lecompte maneuver, as viewed from the patient’s back. AAO, ascending aorta; LPA, left pulmonary Artery; RPA, right pulmonary artery.
Figure 16.26. Coronary artery imaging after ASO by a variety of modalities. C, D, and E are from a single patient with left coronary artery stenosis. A: Parasternal short-axis imaging of the aortic root with color Doppler delineation of flow entering the reimplanted right coronary artery (arrow). Ao, aorta. B: CT angiogram showing the coronary arteries, now reimplanted to the sinuses of the native pulmonary (neoaortic) root. Notice how this root lies directly posterior to the right ventricular outflow tract. RVOT, right ventricular outflow tract; RCA, right coronary artery; LCA, left coronary artery. C:Parasternal short-axis view of neoaortic root, with color Doppler imaging demonstrating aliasing at the origin of the reimplanted left coronary artery (arrow). LCA, left coronary artery. D: Spectral Doppler interrogation of the left coronary artery origin shows bidirectional flow, with the antegrade flow velocity being markedly accelerated (2.4 m/s). E: Angiography (aortic root injection via cardiac catheterization) demonstrates moderate stenosis of the left main coronary artery.
Figure 16.27. Neoaortic root dilation and neoaortic valve insufficiency after ASO. A: Long-axis mid-esophageal TEE view shows a markedly dilated neoaortic valve (arrow) (annulus 3.7 cm) and root (4.5 cm measured offline). By comparison, the neopulmonary valve looks small. B: Color flow view in diastole shows a broad jet of neoaortic insufficiency, which was quantified by other images as severe. LVOT, left ventricular outflow tract.
Postoperative Imaging: Rastelli and Nikaidoh Procedures
A range of etiologies exist for the development of left ventricular outflow tract obstruction in d-TGA and include a posterior malalignment VSD (see Fig 16.23), a subpulmonic fibromuscular ridge, valvar pulmonic stenosis, a bicuspid pulmonary valve, and atrioventricular valve accessory tissue prolapsing into the left ventricular outflow tract (Fig. 16.28). Regardless of the etiology of left ventricular outflow tract obstruction, one of the more common surgical approaches to this variant is the performance of the Rastelli procedure with VSD closure to the anterior aorta and placement of a right ventricle–to–pulmonary artery conduit. Echocardiographic imaging after the Rastelli procedure entails two-dimensional, color, and pulsed Doppler interrogation. The pathway from the left ventricle to the aorta is assessed carefully (Fig. 16.29A), and can be seen from several imaging windows.
The right ventricle–to–pulmonary artery conduit is best imaged from the parasternal or subcostal windows (Fig. 16.30). However, Doppler interrogation may not accurately predict the degree of stenosis as the modified Bernoulli equation is not valid in long-segment obstructive processes. Therefore, whenever possible, right ventricular pressure should be estimated by assessment of the tricuspid regurgitant jet velocity. It is also crucial to take into account the impact of concomitant branch pulmonary artery stenosis.
Figure 16.28. Apical four-chamber view with anterior angulation in a patient with d-TGA and left ventricular outflow tract (LVOT) obstruction. The tricuspid valve septal leaflet is seen to billow into the subpulmonic region, resulting in a narrowed LVOT. RV, right ventricle; LV, left ventricle.
Figure 16.29. A: Parasternal long-axis view of the left ventricular outflow tract status post-Rastelli. The ventricular septal defect patch is seen and the outflow tract appears to be of good caliber. Notice that in order to cross the semilunar valve, blood exiting the left ventricle must take two nearly right-angle turns. LVOT, left ventricular outflow tract; LV, left ventricle; LA, left atrium; VSD, ventricular septal defect. B: Parasternal long-axis view of the left ventricular outflow tract status post–Nikaidoh procedure. Note the smoother contour of the outflow tract, in comparison to the appearance after Rastelli. LVOT, left ventricular outflow tract; LV, left ventricle; LA, left atrium; VSD, ventricular septal defect.
Less frequently employed than the Rastelli procedure, the Nikaidoh procedure is a surgical approach that reconstructs a more normally aligned left ventricular outflow tract (Video 16.7). This typically involves surgical translocation of the aortic root posteriorly. Imaging strategies of the left ventricular outflow tract are similar among the patients who underwent Rastelli or Nikaidoh procedures (Fig 16.29B). Nikaidoh reconstruction techniques of the right ventricular outflow tract can vary and can include direct anastomosis of the pulmonary arteries to the right ventricle (REV procedure), or placement of a conduit. Regardless of the technique employed, stenosis or regurgitation can be present at any level. A detailed evaluation of the reconstruction and branch pulmonary arteries should be performed using 2D, color, and spectral Doppler.
Postoperative Imaging: Atrial Switch Operation (Mustard or Senning Procedure)
Echocardiographic imaging is routinely performed after the atrial switch. The ventricles have a characteristic appearance with a dilated and hypertrophied right ventricle and a compressed, thin-walled left ventricle (Fig. 16.31, Video 16.8). Of chief importance is the assessment of the systemic and pulmonary venous baffles (Figs. 16.32 through 16.36). The atrial switch procedure may result in narrowing of either the systemic venous or pulmonary venous baffles. Transthoracic imaging of these pathways may identify blunted pulsed Doppler venous flow patterns, turbulence by color Doppler interrogation, flow reversal with atrial contraction into the inferior or superior vena cava, or anatomical baffle narrowing by two-dimensional imaging. Given that it has been decades since the atrial switch was common surgical practice in d-TGA, many of these individuals are now adults, often with poor transthoracic windows. In these patients, transesophageal echocardiography may be necessary to delineate the obstructive process. In addition, subsequent catheter-based intervention to ameliorate the obstruction is often best accomplished with associated TEE guidance.
Figure 16.30. Parasternal short-axis view in a patient with d-TGA and left ventricular outflow tract obstruction, status post-Rastelli right ventricle (RV)–to–pulmonary artery (PA) conduit repair using a Contegra bovine jugular vein conduit. A: The RV–to–PA conduit is narrowed at the distal aspect proximal to the PA branches. B: Color Doppler interrogation demonstrates obstruction at the site of narrowing.
Figure 16.31. d-Transposition of the great arteries status post Mustard procedure. Parasternal short-axis imaging demonstrates flattening of the interventricular septum in response to systemic right ventricular pressure. The right ventricle is dilated and hypertrophied. RV, right ventricle; LV, left ventricle.
Postatrial switch procedure baffle leak may also occur (Figs. 16.37 and 16.38). This can also be detected by echocardiographic imaging, with color and pulsed Doppler interrogation identifying the leak between the systemic venous baffle and the right atrium, or between the pulmonary venous baffle and the left atrium. Systemic baffle leaks can also be readily identified via saline contrast injection. If contrast injection into a peripheral arm vein traverses the baffle and enters into the non-baffle portion of the right atrium or into the right ventricle, this provides good evidence for a systemic venous baffle leak. Tandem imaging with angiography and transesophageal echocardiography can then be used to place an occlusion device or covered stent across the baffle leak (see Fig. 16.38).
Figure 16.32. d-Transposition of the great arteries status post Mustard procedure. A: Apical four-chamber view just anterior to the pulmonary venous baffle demonstrates the position of the systemic venous baffle directing blood from the inferior and superior venae cavae to the left ventricle (LV) (arrow). B: Unobstructed systemic venous flow pattern (arrow) directed toward the mitral valve is demonstrated with color Doppler. RV, right ventricle; LV, left ventricle.
Figure 16.33. Parasternal long-axis view shows the left atrial aspect of the systemic venous baffle in a patient status post Mustard procedure for d-TGA. Ao, aorta; LV, left ventricle; LA, left atrium.
POTENTIAL ROLES OF ADDITIONAL IMAGING MODALITIES
Echocardiography remains the workhorse modality for the evaluation of cardiac anatomy and physiology in the vast majority of cases of d-TGA. The most common reason that additional imaging modalities are used is clarification of coronary artery anatomy. When there is uncertainty, most centers rely on cardiac catheterization to provide definitive delineation of the coronary arteries. MRI and CT are potential alternatives but their relative utility will depend on local expertise and hardware. Newer generation CT scanners such as 640-slice or dual-source scanners may be able to evaluate coronary artery anatomy in neonates.
Figure 16.34. Parasternal short-axis view in patient status post–Mustard procedure for d-TGA. A: Venous flow is noted through the systemic venous baffle into the left ventricle (LV) (arrows). RV, right ventricle; Ao, aorta. B: The systemic venous baffle is located just posterior to the aortic root. RV, right ventricle; Ao, aorta.
Figure 16.35. CT angiogram showing the course of intravenous contrast from the inferior vena cava (IVC) through the atrial baffle into the morphologic left ventricle.
Figure 16.36. d-Transposition of the great arteries status post–Mustard procedure (arrow). Apical four-chamber view directed posteriorly to image the pulmonary venous baffle. The right ventricle is dilated and hypertrophied.
Figure 16.37. d-Transposition of the great arteries status post Mustard procedure. A: Right heart imaging via transesophageal echocardiography (TEE) imaging demonstrates a systemic venous baffle leak (arrows). RA, right atrium; AoV, aortic valve; RV, right ventricle. B:Color flow is noted from the systemic venous baffle through a large baffle leak. C: TEE directs placement of an AMPLATZER atrial septal defect occlusion device across the systemic venous baffle defect. The left and right atrial aspects of the device are well seated such that the venous channel is unobstructed and tricuspid valve apparatus function is preserved.
Figure 16.38. Cardiac MRI illustrating the presence of an interatrial baffle leak (arrow). The curved line at the atrial level represents baffle material rather than atrial septum. RV, right ventricle; LV, left ventricle.
In the patient after the ASO, symptoms or findings may raise concerns of the adequacy of coronary artery circulation due to either kinking of these reimplanted vessels or complications associated with their underlying anatomical arrangement (as described earlier). While cardiac catheterization has traditionally supplied this information (see Fig 16.26E), less-invasive modalities are also available. For larger patients with lower heart rates, computed tomography angiography can provide detailed anatomical definition of the coronary artery origins and branches. Often, this requires three-dimensional reconstructive techniques. Cardiac MRI can also define and evaluate reimplanted coronary artery origins, but in a typical clinical practice, spatial resolution will be inferior to CT (see Fig 16.26B). In addition, there may be normal coronary circulation at rest with myocardial ischemia developing only with increases in myocardial demand. In this case, strategies that can be used include stress imaging to delineate myocardial perfusion: nuclear (with sestamibi, as well as other radioisotopes), or cardiac MRI. The difficulty with all of these techniques is the relative lack of expertise in data interpretation at many pediatric centers. In adult centers, stress echocardiography and nuclear medicine are used commonly, allowing providers to obtain adequate experience in data interpretation. This is not necessarily true in the pediatric center, especially in the patient population with complex heart disease. In this setting, difficulties can occur not only due to a lack of adequate expertise in interpreting data derived from these modalities but also because prior surgical intervention may complicate data interpretation.
For patients who underwent atrial switch procedures, echocardiography can be performed to evaluate for baffle obstruction or leaks. Echocardiographic findings can be confirmed with additional imaging such as TEE or cardiac MRI (see Fig 16.38). The latter test can accurately evaluate Qp:Qs.
Three-dimensional echocardiographic imaging may prove useful, especially when there are complexities to the underlying anatomy. Specific instances where three-dimensional imaging may be helpful occur when complex outflow tract anomalies are present. This may allow the surgeon to better understand complex anatomical relationships and potential paths to successful reconstruction, which are more difficult to ascertain by two-dimensional imaging. In addition, three-dimensional imaging may be of benefit in volumetric rendering of the ventricular chambers.
After the atrial or arterial switch procedure, a variety of echocardiographic techniques may prove helpful to assess ventricular dysfunction. These include the myocardial performance index to assess combined systolic and diastolic function. Other parameters of diastolic functional assessment include tissue Doppler, strain, and strain rate. The difficulty with all of these techniques is that only limited data are available delineating normal and abnormal parameters in this population. Correlation of abnormal parameters with functional status, prognosis, or other clinical endpoints is even more challenging. Nevertheless, patients can potentially serve as their own controls. It is our practice to acquire functional data during every postoperative study so that changes occurring during serial assessment may point toward evolving functional disturbances.
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1.A full-term, one-hour-old newborn with a prenatal diagnosis of d-TGA and intact ventricular septum is started on Prostaglandin E1 in the delivery room. On arrival in the Cardiac Intensive Care Unit, the oxygen saturation by pulse oximetry is 50%. What is the most likely explanation for the low oxygen saturation?
A.There is no ductus arteriosus.
B.There is severe pulmonary valve stenosis.
C.There is an associated coarctation of the aorta.
D.The patent foramen ovale is very small.
E.The prenatal diagnosis is wrong.
2.The diagnosis of d-TGA is recognized from the subcostal frontal imaging plane by which of the following observations:
A.The great vessel arising from the left ventricle can be seen to bifurcate.
B.Shunting at the level of the atrial septum is bidirectional.
C.A patent ductus arteriosus is present.
D.There is a ventricular septal defect.
E.There is evidence of abnormal ventricular looping.
3.The diagnosis of d-TGA is supported by the following observation from the parasternal long-axis view:
A.There is discontinuity between the mitral valve and the semilunar valve arising from the left ventricle.
B.The proximal great vessels appear to cross.
C.The proximal great vessels appear to be parallel.
D.The left ventricle appears hypoplastic.
E.The right ventricle appears dilated.
4.Which of the following is the SECOND most common coronary artery pattern in d-TGA?
A.Usual (1AD, Cx; 2R)
B.Single LCA (1AD, Cx,R)
C.Single RCA (2R, AD, Cx)
D.Circumflex from the right (1AD; 2R, Cx)
E.Inverted (1AD, R; 2Cx)
5.A three-day-old newborn with d-TGA has been maintained on Prostaglandin E1 at 0.03 mcg/kg/min since birth. A small (3 mm) muscular ventricular septal defect is noted on his initial echocardiogram. No other ventricular septal defect is identified. The expected shunting pattern is:
A.right ventricle to left ventricle shunting at 3.5 m/s.
B.left ventricle to right ventricle shunting at 2.9 m/s.
C.left ventricle to right ventricle shunting at 4 m/s.
D.no shunting across the defect.
E.low velocity (~ 1 m/s) bidirectional shunting.
6.Which of the following anatomic features of d-TGA would cause consideration of a surgical approach other than an arterial switch operation?
A.Coronary pattern with the circumflex arising from the right coronary artery
B.Moderately hypoplastic pulmonary valve
C.Large perimembranous ventricular septal defect
D.Restrictive foramen ovale
E.Coarctation of the aorta
7.You are performing a postoperative echocardiogram on a three-month-old who underwent an arterial switch operation for uncomplicated d-TGA with intact ventricular septum at seven days of age. Which of the following is statistically the most likely complication to observe?
A.Evidence of severe pulmonary hypertension
B.Supravalvar pulmonic stenosis
C.Left ventricular dilation due to unrecognized significant aortopulmonary collaterals
D.Supravalvar aortic stenosis
E.Residual atrial septal defect
8.You are imaging a 43-year-old male who has had a Mustard procedure for d-TGA. Imaging windows are difficult. You inject agitated saline contrast into an IV in the left arm. Appearance of microcavitations in which of the following structures suggests the presence of a baffle leak?
A.Inferior vena cava
D.Systemic venous baffle
9.You are imaging a 43-year-old male who has had a Mustard procedure for d-TGA. Imaging windows are difficult. You inject agitated saline contrast into an IV in the left arm. Appearance of microcavitations in which of the following structures suggests the presence of obstruction of the superior vena cava?
A.Inferior vena cava
D.Systemic venous baffle
10.You are evaluating a seven-year-old patient who has had an arterial switch procedure and was born with d-TGA. Flow acceleration (>2 m/s) is most likely seen in which of the following structures?
A.Coronary artery origins
C.Right ventricular outflow tract
D.Branch pulmonary arteries
E.Left ventricular outflow tract
1.Answer: D. Typical oxygen saturation in d-TGA with good mixing is in the 80’s. The most common reason for low oxygen saturations in d-TGA is inadequate mixing of the systemic and pulmonary circuits, attributable to a small foramen ovale. Mixing is most effective at the atrial level. In fact, if the atrial communication is small, oxygen saturations are frequently very low despite the presence of a large patent ductus arteriosus. Answer A is wrong. A one-hour-old newborn on Prostaglandin E1 should have a large ductus arteriosus. Neither severe pulmonary valve stenosis nor coarctation of the aorta should cause low oxygen saturations in a newborn on Prostaglandin E1 (answers B and C). Answer E is wrong. There is no reason to think that the prenatal diagnosis is wrong; the presentation described is very compatible with d-TGA with a restrictive foramen ovale.
2.Answer: A. In d-TGA, the pulmonary artery arises from the left ventricle. It is recognized as the pulmonary artery by the fact that it bifurcates. Answers B, C, and D are wrong because these findings are non-specific; i.e., although frequently observed in d-TGA, they can be observed in other forms of congenital heart disease as well. Answer E is incorrect because in d-TGA, the ventricular looping is normal. It is only the ventriculo-arterial alignments that are abnormal.
3.Answer: C. In d-TGA, there is typically fibrous continuity between the pulmonary valve and the mitral valve. Pulmonary-mitral discontinuity should raise the possibility of the diagnosis of double outlet right ventricle. Due to the abnormal ventriculo-arterial alignments, the proximal great vessels are oriented in a parallel fashion, rather than a crossing fashion. This observation is apparent from the parasternal long-axis view. Typically, both ventricles are of normal size in d-TGA.
4.Answer: D. The most common coronary pattern is listed in A. This is designated as “usual” by the Boston Children’s Hospital convention and (1AD, Cx; 2R)—or alternatively (1L, Cx; 2R)—by the Leiden convention. This pattern accounts for ~65% of d-TGA. The second most common pattern is designated “circumflex from the right” by the Boston Children’s Hospital convention and (1AD; 2R, Cx)—or alternatively (1L; 2R, Cx)—by the Leiden convention. This accounts for ~15% of cases of d-TGA. All of the other patterns listed are significantly rarer.
5.Answer: E. In a newborn maintained on Prostaglandin E1, the ductus arteriosus will be large, equalizing the pressure in the two ventricles. Thus, there will be no significant pressure gradient across the defect, despite its relatively small size. There is typically still flow across the defect in both directions but at low velocity.
6.Answer: B. Answer A is incorrect because this coronary artery pattern is considered straightforward to “switch.” Given that the pulmonary valve will become the “neo-aortic” valve after the arterial switch operation, it must be sufficient to allow a full cardiac output across it. A moderately hypoplastic valve is expected to be inadequate to perform an arterial switch. If moderate pulmonary valve hypoplasia is present in conjunction with a favorable type of VSD, this anatomy is usually treated with either a Rastelli or Nikaidoh procedure. A ventricular septal defect or coarctation of the aorta would be surgically addressed during the arterial switch operation. The size of the foramen ovale is not important for the performance of the arterial switch operation and any atrial shunt would be closed in the course of the operation.
7.Answer: B. Supravalvar pulmonic stenosis is the most commonly observed complication of those listed above. While severe pulmonary hypertension or significant aortopulmonary collaterals (Answers A or C) are reported complications for a patient with this history, these are rare. Supravalvar aortic stenosis (Answer D) occurs less commonly than supravalvar pulmonic stenosis. The atrial septal defect (Answer E) is closed as a matter of routine in an arterial switch operation and residual defects are rare.
8.Answer: C. Saline contrast injections can be very useful in the evaluation of patients after atrial switch operation (Mustard or Senning) for d-TGA, especially when imaging windows are limited. In an atrial switch operation, the systemic venous return has been baffled to the left ventricle and the pulmonary venous return has been baffled to the right ventricle to achieve a physiologic repair. An injection in the left arm should traverse the superior vena cava, systemic venous baffle, left ventricle, and pulmonary artery. It would have no reason to traverse the inferior vena cava. Appearance of microcavitations in the right ventricle (which is the systemic ventricle) can only occur if there is a communication between the systemic venous baffle and the pulmonary venous atrium.
9.Answer: A. Saline contrast injections can be very useful in the evaluation of patients after atrial switch operation (Mustard or Senning) for d-TGA, especially when imaging windows are limited. In an atrial switch operation, the systemic venous return has been baffled to the left ventricle and the pulmonary venous return has been baffled to the right ventricle to achieve a physiologic repair. An injection in the left arm should traverse the superior vena cava, systemic venous baffle, left ventricle, and pulmonary artery. If there is obstruction in the superior vena cava, which is a relatively common complication, the saline contrast will typically make its way through veno-venous collaterals such as the azygous vein to the inferior vena cava. Appearance of microcavitations in the right ventricle (which is the systemic ventricle) can only occur if there is a communication between the systemic venous baffle and the pulmonary venous atrium.
10.Answer: D. After the LeCompte maneuver as a part of the arterial switch operation, the branch pulmonary arteries straddle the ascending aorta. It is quite common to observe mild degrees of flow acceleration in the branch pulmonary arteries (typically 1.8-2.5 m/s) and there is generally no significant clinical consequence. Similar degrees of flow acceleration would not be expected in any of the other structures listed.