Echocardiography in Pediatric and Adult Congenital Heart Disease, 2nd Ed.

20. Abnormalities of the Aortic Arch

Anomalies of the aortic arch represent a group of lesions that may occur in isolation or in conjunction with other cardiac defects. In this chapter, aortic arch anomalies will be described as they occur in isolation. Important associations with other cardiac defects will be acknowledged. Aortic arch anomalies to be discussed in this chapter include (a) brachiocephalic branching and vascular rings (including pulmonary artery sling), (b) coarctation of the aorta, and (c) interrupted aortic arch (IAA).

ABNORMALITIES OF BRACHIOCEPHALIC BRANCHING

During normal development, six pairs of arches form the primitive dorsal and ventral aortae (Fig. 20.1). Most portions of the first, second, and fifth arches regress. The carotid arteries are formed by the third arches. The ventral portion of the sixth arch contributes to formation of the pulmonary artery. The right dorsal sixth arch disappears, while the left dorsal portion of the sixth arch becomes the ductus arteriosus. The subclavian arteries are formed by the seven dorsal intersegmental arteries. Involution of the right fourth arch typically results in the usual left aortic arch arrangement. A right aortic arch forms when there is involution of the left fourth arch.

Echocardiographic Assessment of the Aortic Arch

Echocardiographic imaging of the aortic arch is best achieved from the suprasternal notch views. In patients with a left aortic arch, the ascending, transverse, and descending portions of the arch, including the origins of the three arch vessels, can be imaged from the suprasternal long-axis view with the sector plane extending anteriorly from the right nipple to the left scapula posteriorly (Fig. 20.2). If the descending portion of the aorta is not visible, clockwise rotation with minimal angulation of the transducer to the right may identify the presence of a right aortic arch.

Cross-sectional imaging of the transverse aorta is obtained from the suprasternal short-axis view. Anterior angulation of the transducer allows visualization of the first brachiocephalic vessel originating from the arch, which is the innominate artery. The direction in which this vessel courses cephalad is important for determining arch sidedness. The presence of a left aortic arch is confirmed when the innominate artery courses rightward (Fig. 20.3) and the aorta descends leftward (Video 20.1). If the vessel courses leftward (Fig. 20.4) and the aorta descends rightward, a right aortic arch is present (Video 20.2). The innominate artery should be followed distally to its bifurcation into the carotid and subclavian arteries. Echocardiographic demonstration of the bifurcation of the first brachiocephalic vessel in either a left or right aortic arch confirms the absence of a vascular ring. Absence of this bifurcation in a left aortic arch suggests the presence of an aberrant right subclavian artery. A common vascular anomaly, an aberrant right subclavian artery, occurs in 0.5% of humans and carries little, if any, clinical significance (Fig. 20.5). On the other hand, absence of bifurcation of the innominate artery with a right aortic arch suggests the presence of an aberrant left subclavian artery, which has a retroesophageal course and may form a vascular ring in the presence of a left-sided ligamentum arteriosum or ductus arteriosus. Addition of color Doppler is helpful for confirming the bifurcation of the first brachiocephalic vessel.

Figure 20.1. Embryology of the aortic arches. LPA, left pulmonary artery; RPA, right pulmonary artery; RCCA, right common carotid artery; LCCA, left common carotid artery; RSA, right subclavian artery; LSA, left subclavian artery; Ao, aorta. (From Mavroudis and Backer. Pediatric Cardiac Surgery,3rd ed. New York: Mosby; 2003.)

Figure 20.2. Suprasternal long-axis view of normal brachiocephalic branching in a left aortic arch. Asc Ao, ascending aorta; Des Ao, descending aorta; Inn, innominate artery; LCC, left common carotid artery; LSA, left subclavian artery.

Posterior tilting of the imaging plane in the suprasternal short-axis view allows determination of whether the aorta remains on the same side of the spine as it descends within the thorax. The subcostal short-axis view is also helpful for determining which side of the spine the arch is on as it crosses below the diaphragm.

Figure 20.3. Left aortic arch. Bifurcation of the innominate artery into the right common carotid artery (RCC) and right subclavian artery (RSA). The left arch is confirmed when the innominate artery courses rightward.

Another arch variant that deserves mentioning is the cervical aortic arch. Typically presenting as a pulsatile neck mass, the cervical arch extends farther into the neck than a normal arch and is best identified in the suprasternal long-axis view by moving the transducer out of the suprasternal notch and onto the neck.

Figure 20.4. Right aortic arch. The first brachiocephalic branch off the aortic arch courses leftward (arrow).

Figure 20.5. Left aortic arch with aberrant right subclavian artery (RSA) from the descending aorta. LCCA, left common carotid artery; RCCA, right common carotid artery; LSA, left subclavian artery. (From Mavroudis and Backer. Pediatric Cardiac Surgery, 3rd ed. New York: Mosby, 2003.)

VASCULAR RINGS

Vascular rings represent a group of vascular anomalies that cause compression of the trachea, esophagus, or both. Development of a vascular ring depends on the preservation or deletion of specific portions of the rudimentary embryonic aortic arch and may in part be formed by a patent ductus arteriosus or ligamentum arteriosum (Fig. 20.6).

Most children with vascular rings develop symptoms early, usually within the first several weeks to months of life. Symptoms may include breathing difficulty, wheezing, stridor, cough, recurrent respiratory infections, and/or dysphagia. The severity of the clinical presentation depends primarily on the degree of compression by the abnormal vessel on the trachea, bronchus, or esophagus. Respiratory symptoms are often mild and may not be apparent during the newborn period. An infant may gain appropriate weight initially because they often tolerate liquid formula without difficulty. However, once they advance to solid food, their symptoms become more evident and may include apnea or cyanosis. Patients with a double aortic arch tend to present at an earlier age than those with other types of vascular rings. Symptoms are often aggravated by crying, physical exertion, or the presence of a respiratory infection.

Figure 20.6. Right aortic arches. A: Right arch with aberrant left subclavian artery (LSA) from descending aorta. B: Right arch with left ligamentum to descending aorta. C: Right arch with left ligamentum to left subclavian artery (LSA). (From Mavroudis and Backer. Pediatric Cardiac Surgery, 3rd ed. New York: Mosby, 2003.)

Left Aortic Arch with Aberrant Right Subclavian Artery

A left aortic arch with aberrant right subclavian artery is formed when there is regression of the right fourth arch, which lies between the subclavian and carotid arteries. In most cases, a left aortic arch with an aberrant right subclavian artery is not considered a clinically significant finding. However, when a right-sided ductus arteriosus or ligamentum arteriosus is present, a complete vascular ring can be formed. Inability to visualize the bifurcation of the right innominate artery originating from a left aortic arch suggests the presence of a left arch with aberrant right subclavian artery (Fig 20.7). Complete sweeps of the aortic arch from the suprasternal long- and short-axis views demonstrate the origin of the aberrant right subclavian artery from the upper descending thoracic aorta (Video 20.3). Additional imaging should focus on determining whether a right-sided ductus arteriosus is present.

Right Aortic Arch with Aberrant Left Subclavian Artery

Involution of the embryonic left fourth arch results in formation of a right aortic arch. Mirror-image branching is present in 35% of patients with a right aortic arch and occurs when there is persistence of the right fourth arch and disappearance of the left arch between the left subclavian artery and the dorsal descending aorta. A vascular ring is formed when the ligamentum arteriosum originates from the descending aorta.

Echocardiographic identification of the first brachiocephalic vessel coursing leftward and superiorly in the suprasternal short-axis view, confirms the presence of a right aortic arch. Absence of the bifurcation of the left innominate artery with a right aortic arch suggests the presence of an aberrant left subclavian artery (Fig 20.8, Video 20.4). Additional imaging modalities may be needed to confirm the presence of a left ligamentum arteriosum.

Figure 20.7. Left aortic arch with aberrant left subclavian artery. Suprasternal notch imaging showing innominate artery coursing rightward confirming left aortic arch; but it is not bifurcating (red arrow) which suggests an aberrant right subclavian artery (yellow arrow).

Figure 20.8. Right aortic arch with aberrant right subclavian artery. Suprasternal notch imaging showing innominate artery coursing leftward (Inn) confirming right aortic arch; but it is not bifurcating which suggests an aberrant left subclavian artery (LSA). The aorta descends rightward (Des Ao).

Right Aortic Arch with Retroesophageal Segment and Left Descending Aorta

Persistence of the embryonic right fourth arch with deletion of the left arch between the left carotid and left subclavian arteries results in a right aortic arch with a retroesophageal course of the left subclavian artery (Fig. 20.6). In 65% of patients with a right aortic arch, the left subclavian artery arises from the descending aorta and courses to the left behind the esophagus. In this case, a vascular ring may be formed when there is a ligamentum arteriosum extending from the descending aorta to the left pulmonary artery.

In the suprasternal long-axis view, echocardiographic identification of this arch anomaly may be difficult because the descending aorta descends to the left despite the arch being rightward. Often associated with a cervical arch, the arch can have a hairpin appearance. The transducer may need to be moved onto the neck to accurately demonstrate branching. The diagnosis of a right aortic arch is confirmed when the first brachiocephalic vessel courses leftward and superiorly.

Double Aortic Arch

A double aortic arch occurs when there is persistence of both the right and left aortic arches. A ring is formed around the trachea and esophagus by the two arches, as they arise from the ascending aorta. The posterior arch is rightward and typically the dominant arch in 75% of cases, giving rise to the right carotid and subclavian arteries. The anterior, leftward arch is usually smaller and gives rise to the left carotid and subclavian arteries. In 20% of cases, the left arch may be the dominant arch, while in 5% of cases the arches may be equal in size. Approximately 20% of patients with double aortic arch have associated congenital heart disease, including tetralogy of Fallot, ventricular septal defect, coarctation, patent ductus arteriosus, transposition of the great arteries, and truncus arteriosus.

Subcostal imaging of left ventricular outflow may show bifurcation into two separate arches and is often the first clue that a double aortic arch is present. From the suprasternal long-axis view, counterclockwise rotation of the transducer will bring both arches into view (Fig. 20.9, Video 20.5). Color Doppler is helpful in confirming these findings and in identifying the origins of the arch vessels.

Pulmonary Artery Sling

In this rare vascular malformation, the left pulmonary artery originates from the right pulmonary artery and passes between the esophagus and trachea as it courses toward the left hilum (Fig. 20.10). Symptoms are typically related to tracheal compression and include respiratory distress, stridor, cyanosis, wheezing, and retractions. Additional cardiac defects are often present and can include patent ductus arteriosus, atrial septal defect, ventricular septal defect, pulmonary atresia, left superior vena cava, and single ventricle. Tracheal stenosis, complete tracheal rings, and tracheoesophageal fistula are also common extracardiac associations.

Figure 20.9. Double aortic arch. Suprasternal notch imaging showing right aortic arch descending rightward (red arrow), smaller left aortic arch descending leftward (yellow arrow), and respective right (green arrow) and left (orange arrow) innominate arteries which will branch into common carotid and subclavian arteries.

Figure 20.10. Diagram demonstrating a pulmonary artery sling. The left pulmonary artery (LPA) originates from the right pulmonary artery (RPA) rather than the normal bifurcation from the main pulmonary artery (MPA). (From Mavroudis and Backer. Pediatric Cardiac Surgery, 3rd ed. New York: Mosby, 2003.)

Although there may be a suggestion of an abnormal origin of the left pulmonary artery in the subcostal and parasternal short-axis views, the suprasternal long-axis view provides the best acoustic window for imaging of a pulmonary artery sling. In this view, the left pulmonary artery is seen arising from the right pulmonary artery and coursing leftward, behind the trachea to the left lung (Fig. 20.11). Color and spectral Doppler are helpful for differentiating the left pulmonary artery from other structures that may be mistaken for the left pulmonary artery, such as a patent ductus arteriosus or left atrial appendage.

Additional Imaging Modalities

The diagnosis of aortic arch anomalies such as vascular rings can often be made echocardiographically. However, because of limited acoustic windows, it may not be the dominant imaging modality used. Initial evaluation of a patient with suspected vascular ring typically includes a chest radiograph for determination of arch sidedness and its relation to the trachea. When arch sidedness is not clearly evident, the presence of a double aortic arch should be suspected. Narrowing of the trachea in the lateral images may be seen with a right aortic arch or double aortic arch (Fig. 20.12). Unilateral hyperinflation of the right lung suggests the presence of a pulmonary artery sling.

Figure 20.11. Pulmonary artery sling. Parasternal image demonstrating origin of the left pulmonary artery (arrow) from the right pulmonary artery. Ao, aorta.

The barium esophagogram has traditionally been used for the diagnosis of vascular rings. Indentation of the barium-filled esophagus by the anomalous arch vessel produces characteristic patterns for each specific lesion. For example, a right aortic arch with left ligamentum or double aortic arch produces an indentation of the posterior aspect of the esophagus (Fig. 20.13A). A double aortic arch results in bilateral compression of the esophagus in the anteroposterior view (Fig. 20.13B). A right aortic arch with a retroesophageal left subclavian artery creates an oblique indentation in the esophagus angled toward the left shoulder, whereas an aberrant right subclavian artery generates a high posterior oblique indentation of the esophagus directed from left to right. An anterior esophageal indentation is seen with pulmonary artery sling (Fig. 20.14).

Bronchoscopy may be helpful for establishing the diagnosis in children who present with respiratory distress in whom a vascular ring is suspected. Compression of the trachea can be seen with a double aortic arch or right aortic arch with a left ligamentum. Bronchoscopy can be used to exclude other causes of respiratory compromise, such as the presence of tracheal rings with a pulmonary artery sling.

Additional imaging modalities that provide accurate diagnosis of aortic arch anomalies, such as vascular rings, include computed tomography (CT) scanning and magnetic resonance imaging (MRI). Because not all vascular rings are completed by a patent vascular structure (i.e., some are completed by a ligamentum arteriosum or atretic lesser arch), recognition of the arterial branching pattern, arch sidedness, and narrowing of the airway remain important clues in establishing a correct diagnosis. CT scanning is often preferred because it can be performed quickly and does not necessarily require sedation. CT and MRI have essentially obviated the need for tracheograms and cardiac catheterization in the diagnosis of vascular rings (Figs. 20.15 through 20.18).

COARCTATION OF THE AORTA

Coarctation of the aorta represents a congenital narrowing of the aorta, most often occurring just distal to the left subclavian artery and adjacent to the site of insertion of the ductus arteriosus. Coarctation occurs in 5% to 8% of patients with congenital heart disease and is slightly more predominant in males. Common associated anomalies include patent ductus arteriosus, bicuspid aortic valve, ventricular septal defect, and mitral valve abnormalities. More complex defects that may be seen in conjunction with coarctation include Shone syndrome, hypoplastic left heart syndrome, tricuspid atresia with transposed great arteries, and other forms of transposition, in which coexisting subaortic stenosis may lead to development of arch obstruction. Additional arterial abnormalities, such as stenosis of the origin of the left subclavian artery and anomalous origin of the right subclavian artery distal to the site of coarctation, have also been reported.

The clinical presentation of coarctation may be variable and depends on patient age, lesion severity, and location of the narrowing, as well as the presence and severity of additional cardiac defects. As the name implies, ductal-dependent, or critical, coarctation typically presents with cardiovascular collapse early in the newborn period once the ductus closes. The clinical presentation of severe coarctation may be delayed to later in infancy and includes symptoms of congestive heart failure, such as respiratory distress, pallor, and poor feeding. Children with less severe narrowing of the aorta may not have any significant symptoms until later in life, in which case they may present with systemic hypertension and their femoral pulses may be absent or weak and delayed in comparison with their brachial pulses.

Two-Dimensional Imaging of Coarctation

Although coarctation of the aorta is best imaged from the suprasternal notch view, there are several intracardiac findings demonstrated in a combination of views that should suggest the possibility of arch obstruction. These include the presence of left ventricular obstruction, right or left ventricular hypertrophy and/or dysfunction without an obvious etiology, and reduced or absent pulsatility of the abdominal aorta.

The subcostal view is useful for demonstrating the position of the aorta as it traverses the diaphragm. The transducer is positioned just below the xiphoid process with the plane of sound oriented in a coronal section for the short-axis view. From here, 90-degree rotation of the transducer with leftward or rightward angulation (depending on position of the aorta in the abdomen) in the sagittal plane demonstrates a long segment of the descending, abdominal aorta. In small infants, it may be possible to visualize the entire aorta by scanning in a cranial direction in this plane. Left atrial enlargement, right ventricular enlargement, and dilation of the pulmonary artery may be evident. The presence of ventricular dysfunction should lead to careful assessment of both outflow tracts for potential obstruction.

Figure 20.12. A: Frontal radiograph with tracheal narrowing consistent with a double aortic arch. B: Lateral radiograph demonstrating tracheal narrowing consistent with either a right or double aortic arch. (Courtesy of Cynthia Rigsby, MD.)

Figure 20.13. A: Barium esophagram from the lateral projection demonstrating an indentation (black arrow) consistent with a vascular ring. B: Barium esophagram demonstrating bilateral compression (white arrows) consistent with a double aortic arch. (Courtesy of Cynthia Rigsby, MD.)

Figure 20.14. Barium esophagram with anterior indentation (white arrow) typical of a pulmonary artery sling. (Courtesy of Cynthia Rigsby, MD.)

Figure 20.15. Chest CT scan demonstrating tracheal compression from a vascular ring. (Courtesy of Cynthia Rigsby, MD.)

Figure 20.16. Tracheogram with compression from a vascular ring. (Courtesy of Cynthia Rigsby, MD.)

Parasternal long-axis imaging shows right ventricular dilation and hypertrophy in coarctation. The left ventricle may also be dilated with poor systolic function. Anterior angulation of the transducer allows visualization of the dilated pulmonary artery and ductus arteriosus, if one is present. A high left or right parasternal view with angulation of the transducer toward the left shoulder may also reveal the site of coarctation. The parasternal short-axis view may demonstrate a bicuspid aortic valve or ventricular dilation. M-mode is used to quantify left ventricular wall thickness, chamber dimensions, left ventricular mass, and systolic function.

Figure 20.17. MRI scan demonstrating a pulmonary artery sling. The trachea (arrow head) is compressed by the left pulmonary artery (thin arrow). Main pulmonary artery (thick arrow). (Courtesy of Cynthia Rigsby, MD.)

Figure 20.18. MRI scan demonstrating a double aortic arch (arrows). (Courtesy of Cynthia Rigsby, MD.)

The apical view may reveal chamber enlargement and hypertrophy and allows additional assessment of the outflow tracts. Ventricular function can be further quantified by calculation of left ventricular ejection fraction.

The suprasternal arch view is considered the best window for imaging the aortic arch (Fig. 20.19). From the long-axis orientation, the aortic arch can usually be imaged in its entirety. The area of coarctation is typically found in the region of the left subclavian artery and is most often characterized by an echo-dense shelf of tissue arising from the posterior aspect of the aorta (Videos 20.6 and 20.7). It is important not to confuse an anterior shelf, which may be present in the location of the ductal ampulla, as coarctation. On occasion, a long segment narrowing may be present or the narrowed segment may be located more distally in the aorta. For this reason, the entire aorta must be imaged so as not to miss this important diagnosis. The transverse aortic arch may be hypoplastic in neonates with coarctation and can contribute to residual obstruction following repair. Additional features of coarctation include an increased distance between the left common carotid artery and left subclavian artery and an isthmus diameter of less than two-thirds the diameter of the descending aorta. Determination of arch sidedness and branching, which can be obtained from the suprasternal short-axis view, is also important in the presurgical evaluation of patients with coarctation. If imaging of the aorta and arch is inadequate or in the presence of a large ductus arteriosus, other imaging modalities such as CT and MRI may be necessary to better define arch anatomy before surgical repair.

Doppler Features of Coarctation

Color Doppler demonstrates an area of flow acceleration proximal to the narrowed aortic segment, thus confirming the diagnosis of coarctation (Fig. 20.20). In severe coarctation, there is often aliasing of the color flow jet above the Nyquist limit, with continuation of flow in both systole and diastole. The width of the color jet has been shown to correlate well with the diameter of the coarctation measured angiographically.

Figure 20.19. Coarctation of the aorta. Suprasternal long-axis view demonstrating a posterior shelf (yellow arrow).

Figure 20.20. Coarctation of aorta. 2-dimensional imaging (left) demonstrates a discrete coarctation (arrow). Color Doppler (right) demonstrates aliased flow in the area of obstruction (yellow arrow).

In the presence of a significant coarctation, the pulsed Doppler examination of the abdominal aorta in the subcostal view will show a dampened, low-velocity signal with continuation of flow throughout diastole and absence of early diastolic flow reversal (Fig. 20.21). Time to peak velocity is delayed, and the mean acceleration rate is decreased (Fig. 20.22).

In the suprasternal notch view, placement of the pulsed Doppler sample volume parallel to, and just proximal to the site of coarctation, reveals increased flow velocity, usually exceeding the Nyquist limit. For this reason, use of guided and nonguided continuous-wave Doppler is necessary. The characteristic Doppler flow pattern is described as “sawtooth” in appearance, with antegrade flow extending into diastole. Two populations of flow are typically present and superimposed on one another: a high-velocity, outer envelope reflects flow across the site of coarctation (V2), and a lower-velocity, dense inner envelope represents flow proximal to the coarctation (V1) (Fig. 20.23). Because additional left heart obstructive lesions may be present in patients with coarctation, the velocity proximal to the site of coarctation may be increased. If the proximal velocity is greater than 1 m/s, then the modified Bernoulli equation (ΔΡ = 4[V22 – V12]) should be used to calculate the maximum instantaneous gradient across the area of coarctation. Because the systolic velocities may overestimate the true blood pressure gradient, the mean gradient may be more reflective of the actual blood pressure gradient.

Certain limitations exist with Doppler evaluation of the coarctation gradient. It is important to note that in the presence of a large ductus arteriosus or significant collateral flow, the descending aortic Doppler pattern may be normal. If the Doppler beam is not aligned parallel to flow, the coarctation gradient may be underestimated. The severity of obstruction may also be masked by low cardiac output.

The presence of significant arch obstruction predisposes the left ventricle to increased afterload and the development of left ventricular hypertrophy. Diastolic dysfunction may be present and is manifested by abnormal mitral Doppler filling patterns consistent with impaired left ventricular relaxation that often persist after repair.

Imaging Following Coarctation Repair

Following successful coarctation repair without residual arch obstruction, it is not uncommon to detect an increase in the systolic peak velocity across the site of surgical repair. The Doppler profile is otherwise normal, with absence of continuation of flow in diastole. When a residual coarctation is present, the Doppler pattern is similar to that seen before repair with a delayed upstroke and continuation of flow into diastole. Abdominal aortic pulsatility may also be diminished. Color Doppler is helpful for identifying the site of residual obstruction.

Abnormalities of left ventricular systolic and diastolic function have been shown to persist, even after successful coarctation repair. These include decreased early diastolic filling with compensatory increased late diastolic filling during mitral inflow. Increased fractional shortening, greater left ventricular mass index, and lower left ventricular wall stress have also been reported at long-term follow-up, despite the absence of residual arch obstruction.

Figure 20.21. Abdominal aortic Doppler flow patterns. A (normal): Pulsed-wave Doppler evaluation of the abdominal aorta at the diaphragm demonstrates a brisk upstroke and downstroke with presence of an early diastolic flow reversal (EDR) signal (arrow). The EDR signal excludes proximal obstruction in the thoracic aorta. B (coarctation): Upstroke and downstroke are delayed and the EDR is absent.

Associated defects that are commonly seen with coarctation include bicuspid aortic valves, ventricular septal defects and multiple left-sided obstructive lesions. Following surgical repair of coarctation, the hemodynamic severity of these lesions may progress or become more apparent. Therefore, careful echocardiographic evaluation of the intracardiac anatomy and function should be included in the postoperative examination.

Interrupted Aortic Arch

Interrupted aortic arch (IAA) represents the most severe form of coarctation. This rare anomaly accounts for 1.5% of all congenital heart defects. It is often associated with other cardiac abnormalities, including a patent ductus arteriosus, ventricular septal defect, subaortic stenosis caused by posterior malalignment of the conal septum, bicuspid aortic valve with hypoplasia of the aortic annulus, and atrial septal defect. Less commonly associated cardiac anomalies include truncus arteriosus and aortopulmonary window. A complete echocardiographic evaluation of the intracardiac anatomy is warranted to identify additional abnormalities.

Figure 20.22. Abdominal aortic pulsed-wave Doppler flow in a patient with severe coarctation of aorta.

Figure 20.23. Continuous-wave Doppler (CW) assessment of coarctation. This CW signal was obtained with a nonimaging probe from the suprasternal notch. Two populations of flow are demonstrated: flow proximal to the coarctation (V1) and high-velocity flow across the coarctation site (V2).

Interruption of the aortic arch may occur at three sites (Fig. 20.24). In IAA type A, the interruption occurs between the left subclavian artery and descending aorta at the level of the isthmus. IAA type B is the most common form and occurs between the left common carotid artery and the left subclavian artery (Video 20.8). A ventricular septal defect is present in up to 80% of cases, and aberrant origin of the right subclavian artery is also commonly associated with this type of interruption. IAA type C is the least frequent form of arch interruption and occurs between the innominate artery and left carotid artery.

Infants with IAA typically present with symptoms of cardiovascular collapse and pronounced acidosis on ductal closure. Injury to the heart muscle is reflected as poor cardiac output. Poor perfusion to the lower body causes ischemic injury to the liver, intestines, and kidneys. Severe systemic acidosis ultimately results in damage to the brain.

Figure 20.24. Three sites of aortic arch interruption are demonstrated. A: Interruption between the left subclavian artery (LSA) and descending aorta (Desc Ao). B: Interruption between the left common carotid artery (LCCA) and LSA. C: Interruption between innominate artery (IA) and LCCA. DA, ductus arteriosus; MPA, main pulmonary artery. (From Mavroudis and Backer. Pediatric Cardiac Surgery, 3rd ed. New York: Mosby, 2003.)

Two-Dimensional Imaging of Interrupted Aortic Arch

As with coarctation, IAA is best imaged from the suprasternal short-axis view. From this view, the ascending portion of the aorta appears smaller than the descending aorta. Inability to demonstrate continuity between the ascending and descending portions of the aortic arch confirms the diagnosis of arch interruption. From a surgical perspective, it is important to note whether the distance between the proximal and distal segments is long or short and to accurately determine which vessels arise from the proximal and distal aorta.

The type of IAA is determined by the position of the arch vessels in relation to the site of interruption. Origin of the subclavian artery from the distal descending aorta occurs with type B interruption (interruption between the left carotid and left subclavian arteries). This is best shown in the suprasternal long-axis view with the plane of the sound tilted toward the left (Fig. 20.25). In type A interruption (interruption between the left subclavian artery and the descending aorta), all of the head and neck vessels arise from the proximal aorta. Type C interruption is rare and occurs between the innominate and left subclavian artery.

Figure 20.25. Interrupted aortic arch type B. Suprasternal long-axis image demonstrates the innominate artery (asterisk) and left common carotid artery (double asterisk) arising from the aortic arch. The left subclavian artery arises distal to the interruption from the descending aorta.

Doppler Features of Interrupted Aortic Arch

In the presence of a widely patent ductus arteriosus, the color flow Doppler pattern in the descending aorta may be normal, and the spectral Doppler pattern may show normal pulsatility. As the ductus closes, the color flow pattern will demonstrate a high-velocity jet in the descending aorta, similar to that seen with coarctation.

Imaging Following Interrupted Aortic Arch Repair

The echocardiographic examination following repair of IAA should focus on evaluating for residual obstruction at the site of the anastomosis. The severity of residual obstruction can be determined by employing the Doppler techniques described earlier, as well as assessing for abdominal aortic pulsatility, and the peak and mean Doppler gradients through the site of residual narrowing. In the presence of residual obstruction, the Doppler pattern will demonstrate a delay in upstroke and continuous flow in diastole, similar to that seen with residual coarctation.

Acknowledgment

The authors would like to acknowledge Dr. Constantine Mavroudis and Dr. Cynthia Rigsby for their contributions.

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Questions

1.How many pairs of arches are from the primitive dorsal and ventral aortae?

A.2

B.3

C.4

D.5

E.6

2.Involution of what arch results in the usual left aortic arch arrangement?

A.Left fourth arch

B.Left sixth arch

C.Right fourth arch

D.Right sixth arch

E.Third arch

3.What portion of the arch forms the left ductus arteriosus?

A.Right ventral portion of sixth arch

B.Left dorsal portion of sixth arch

C.Right dorsal portion of sixth arch

D.Left ventral portion of sixth arch

E.Left third arches

4.Which planes or views will give the best view of the aortic arch—the ascending, transverse, and descending portions of the arch, including the origins of the three arch vessels?

A.Suprasternal long-axis view

B.Subcostal sagittal view

C.Parasternal short-axis view

D.Parasternal long-axis view

E.Apical five-chamber view

5.How do you confirm the presence of a left aortic arch?

A.First brachiocephalic vessel courses leftward and aorta descends leftward.

B.First brachiocephalic vessel courses leftward and the aorta descends rightward.

C.First brachiocephalic vessel courses rightward and the aorta descends leftward.

D.First brachiocephalic vessel courses rightward and the aorta descends rightward.

E.Aorta descends leftward as it crosses the spine in the abdomen.

6.Which of the following is a common vascular anomaly, occurs in 0.5% of humans, and carries little, if any, clinical significance?

A.Right aortic arch with aberrant left subclavian artery

B.Left aortic arch with aberrant right subclavian artery

C.Double aortic arch with atretic left arch

D.IAA (Type B) with ductal origin of the left subclavian artery

E.Right aortic arch with mirror-image branching

7.What percent of patients with double aortic arch have associated congenital heart disease?

A.10%

B.20%

C.30%

D.40%

E.50%

8.How is a pulmonary artery sling defined?

A.Left pulmonary artery originating from the right pulmonary artery and passing between the esophagus and trachea as it courses toward the left hilum.

B.Right pulmonary artery originating from the left pulmonary artery and passing between the esophagus and trachea as it courses toward the right hilum.

C.Left pulmonary artery originating from the aorta and passing anterior to the esophagus and trachea as it courses toward the left hilum.

D.Right pulmonary artery originating from the aorta and passing posterior to the esophagus and trachea as it courses toward the hilum.

E.Main pulmonary artery originating from the aorta and passing between the esophagus and trachea as it courses to the lungs.

9.The Doppler pattern in the figure is consistent with which of the following?

A.Aortopulmonary window

B.Coarctation of aorta

C.Large patent ductus arteriosus

D.Arteriovenous malformation

E.Aortopulmonary collateral

10.Where is the area of coarctation typically located?

A.Between the innominate and left carotid arteries

B.Between the left carotid and left subclavian arteries

C.In the region of the left subclavian artery and is most often characterized by an echo-dense shelf of tissue arising from the posterior aspect of the aorta

D.At the site where the aorta crosses the diaphragm

E.In the abdominal aorta

Answers

1.Answer: E. There are a total of six pairs of primitive dorsal and ventral aortae. The first, second, fifth, and right dorsal sixth arch normally regress. The third arches form the carotid arteries. The ventral portion of the sixth arch forms the pulmonary arteries. The left dorsal sixth arch forms the left ductus arteriosus. The fourth arch forms the aortic arch: involution of the left fourth aortic arch leads to a right aortic arch and involution of the right fourth aortic arch leads to a left aortic arch.

2.Answer: C. Involution of the right fourth arch leads to a right aortic arch. Involution of the left arch results in a right aortic arch. The third arches form the carotid arteries. The ventral portion of the sixth arch forms the pulmonary arteries. The left dorsal sixth arch forms the left ductus arteriosus. The right dorsal sixth arch normally regresses.

3.Answer: B. The left dorsal sixth arch forms the left ductus arteriosus. The right dorsal sixth arch normally regresses. The ventral portion of the sixth arch forms the pulmonary arteries. The third arches form the carotid arteries.

4.Answer: A. Suprasternal long-axis view is best for visualization of the entire aortic arch. The apical five-chamber view will only show the ascending aorta. Subcostal views can show the full arch sometimes in infants but is not confirmatory for branching and sidedness. The parasternal short-axis view only shows the aortic valve.

5.Answer: C. The presence of a left aortic arch is confirmed when the first brachiocephalic vessel, the innominate artery, courses rightward and the aorta descends leftward. If the first brachiocephalic vessel courses leftward and aorta descends rightward, a right aortic arch is present.

6.Answer: B. A left aortic arch with aberrant right subclavian artery can be a normal finding without any significant clinical concern because it does not form a vascular ring.

7.Answer: B. Twenty percent of patients with a double aortic arch have associated congenital heart disease.

8.Answer: A. The left pulmonary artery originating from the right pulmonary artery and passing between the esophagus and trachea as it courses toward the left hilum forms a pulmonary artery sling.

9.Answer: B. This Doppler pattern is consistent with coarctation of the aorta.

10.Answer: C. Coarctation is most commonly located between the left subclavian artery and the ductal ampulla and is characterized by a shelf of tissue arising from the posterior aspect of the aorta.