Introduction	Choose Top of pageABSTRACTIntroduction <<Types of Interrupted Aort...Pathogenesis and Associat...Imaging of Interrupted Ao...Prognosis and TreatmentConclusionsReferencesCITING ARTICLES

Interrupted aortic arch (IAA) is defined as a lack of luminal continuity between the ascending and descending thoracic aorta. This discontinuity may be complete or it may be spanned by an atretic fibrous band [1]. The condition is extremely rare, representing less than 1.5% of congenital heart disease cases [2]. Approximately 3-20 in 1 million live births are affected by a form of IAA. This vascular anomaly was initially described in 1778 [3] and was first surgically repaired in 1954 [4].

Types of Interrupted Aortic Arch	Choose Top of pageABSTRACTIntroductionTypes of Interrupted Aort... <<Pathogenesis and Associat...Imaging of Interrupted Ao...Prognosis and TreatmentConclusionsReferencesCITING ARTICLES

Traditionally, IAA has been classified into three discrete types on the basis of the location of the aortic arch discontinuity [1, 5] (Figs. 1A, 1B, and 1C). Type A is an interruption just distal to the left subclavian artery and traditionally makes up approximately one third of IAA cases. The type B defect occurs between the left common carotid and left subclavian arteries and is responsible for approximately two thirds of the cases. Type C is the rarest type, occurring in less than 5% of IAA cases. This form is the most proximal defect, occurring between the innominate and left common carotid arteries. Schreiber et al. [6] reviewed 95 cases of IAA and classified 13% as type A, 84% as type B, and 3% as type C.

Pathogenesis and Associated Cardiac Defects	Choose Top of pageABSTRACTIntroductionTypes of Interrupted Aort...Pathogenesis and Associat... <<Imaging of Interrupted Ao...Prognosis and TreatmentConclusionsReferencesCITING ARTICLES

Although the exact cause of IAA is uncertain, several theories have been proposed. These theories most commonly are based on the supposition that blood flow during embryogenesis directly affects the enlargement and involution of blood vessels [1]. Some investigators have theorized that conditions that cause abnormally decreased blood flow through the aortic arch contribute to the development of IAA.

Regarding embryology, type A is likely the result of abnormal regression of the left fourth aortic arch after ascension of the left subclavian artery to its expected position. Type B occurs when the left fourth aortic arch regresses before normal ascension of the left subclavian artery to its expected position. Type C is seen when the ventral portion of the left third aortic arch and left fourth aortic arch involute, and there is a persistent ductus caroticus, a structure that normally regresses [1].

IAA is associated with additional cardiovascular anatomic defects in up to 98% of the cases. The most commonly observed cardiovascular anomaly is a patent ductus arteriosis, occurring in approximately 97% of patients with IAA [1]. This vascular structure is required to supply blood flow beyond the interruption to the descending thoracic aorta. Ventricular septal defects are also typically present, occurring in approximately 90% of individuals with IAA [7, 8]. Conditions that decrease blood flow to the aortic arch, including subaortic stenosis, bicuspid aortic valve, truncus arteriosis, and aortopulmonary window, have been associated with IAA [1, 7, 9]. Rarely, IAA is an isolated finding without another associated cardiac defect, which suggests the possibility that an extrinsic compressive or mechanical force is causative.

Approximately 50% of IAA cases are associated with a chromosome 22q11.2 deletion, particularly in the presence of a right descending thoracic aorta. This chromosomal abnormality is seen in up to 75% of patients with type B IAA. Conversely, it is relatively rare in patients with type A, which suggests either another genetic or a mechanical cause. This chromosomal deletion is observed in both DiGeorge and velocardiofacial syndromes, and it is associated with a variety of conotruncal cardiac anomalies. IAA affects up to 42% of individuals with DiGeorge syndrome [1, 9].

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Fig. 1A —Drawings show three types of interrupted aortic arch. Arrow = patent ductus arteriosus. Type A interruption occurs just distal to left subclavian artery. Patent ductus arteriosus provides blood flow to descending thoracic aorta.

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Fig. 1B —Drawings show three types of interrupted aortic arch. Arrow = patent ductus arteriosus. Type B interruption occurs between left common carotid and left subclavian arteries. Patent ductus arteriosus provides blood flow to left subclavian and descending thoracic arteries.

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Fig. 1C —Drawings show three types of interrupted aortic arch. Arrow = patent ductus arteriosus. Type C interruption occurs between innominate and left common carotid arteries. Patent ductus arteriosus provides blood flow to left common carotid, left subclavian, and descending thoracic arteries.

Imaging of Interrupted Aortic Arch	Choose Top of pageABSTRACTIntroductionTypes of Interrupted Aort...Pathogenesis and Associat...Imaging of Interrupted Ao... <<Prognosis and TreatmentConclusionsReferencesCITING ARTICLES

Proper surgical planning requires an accurate diagnostic imaging evaluation to correctly characterize aortic and cardiac anatomy and define the exact type of IAA. Anatomic features that must be identified include the following: location and length of the aortic vascular defect, caliber of the thoracic aorta proximal and distal to the interruption, branching pattern and origins of the great vessels, location and patency of the ductus arteriosus, appearance of the ventricular outflow tracts, and presence of any other cardiac anomalies.

Multiple imaging techniques have been described in the evaluation of patients with suspected IAA. Echocardiography is considered to be the primary imaging technique for the workup of this entity [10, 11]. It has the advantages of being portable and not using ionizing radiation. Although this imaging technique usually provides excellent anatomic definition of the heart, evaluation of the aorta and great vessels can occasionally be limited. Thus, echocardiography may or may not be able to define the exact site of the aortic arch interruption and its relationship to the origins of the great vessels.

In the past, catheter angiography also performed an important role in the evaluation of patients with suspected IAA [12]. However, this imaging technique both is invasive and requires ionizing radiation. The use of noninvasive CT angiography has recently been described in the evaluation of this entity [13, 14], although concerns about radiation exposure also afflict this imaging technique. CT angiography may be useful in certain circumstances, such as when there is no access to echocardiography or MRI.

The use of MRI, including MR angiography, has been described in the evaluation of numerous complex congenital heart defects including IAA [11, 15-18]. MRI can accurately characterize cardiovascular anatomy, including that of the thoracic aorta and great vessels and coexisting cardiac anomalies. In addition, MRI can also provide useful information regarding cardiac chamber and valve function. Like echocardiography, MRI is noninvasive and does not require ionizing radiation. Sedation or general anesthesia may be required to limit motion-related artifacts in the pediatric population.

Multiple MRI techniques can be used to evaluate the thoracic aorta and heart in cases of suspected IAA. MRI sequences can be performed both with and without IV gadolinium-containing contrast material. Unenhanced evaluation may include double inversion recovery fast spin-echo “black blood,” gradient-recalled echo “white blood,” and balanced (e.g., 2D and 3D balanced-steadystate free precession [SSFP]) imaging sequences. Balanced SSFP imaging sequences can be performed in any plane, including a sagittal oblique plane that displays both ascending and descending thoracic aorta, and may be acquired as cine loops. Gadolinium-enhanced 3D gradient-recalled echo MR angiography sequences are also frequently used, and they can be performed in either the sagittal or coronal plane.

Several MRI findings suggest the diagnosis of IAA. The most specific imaging finding is nonvisualization of a portion of the aortic arch (Figs. 2A, 2B, 2C, 2D, 2E, 2F, 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, 5A, 5B, 5C, 6A, 6B, 6C, and 6D). Such a defect should be confirmed on more than one imaging sequence and in multiple planes if possible. Multiplanar reformatted imaging can be helpful when using gadolinium-enhanced 3D MR angiography and 3D balanced SSFP imaging.

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Fig. 2A —1-week-old female neonate with type A interrupted aortic arch, ventricular septal defect, and patent ductus arteriosus. Coronal gadolinium-enhanced MR angiography image shows small-caliber ascending aorta (AA) arising from left ventricle. Right common carotid artery (RCCA) and main pulmonary artery (MPA) can also be seen. Incidental note is also made of venous contamination (V).

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Fig. 2B —1-week-old female neonate with type A interrupted aortic arch, ventricular septal defect, and patent ductus arteriosus. Left common carotid artery (LCCA) arises from aortic arch, and origin of right pulmonary artery (RPA) is visualized at same level.

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Fig. 2C —1-week-old female neonate with type A interrupted aortic arch, ventricular septal defect, and patent ductus arteriosus. Aortic arch terminates as left subclavian artery (LSCLA). There is apparent interruption (INT) of aortic arch between left subclavian artery and descending thoracic aorta. Both right and left vertebral arteries (RVA and LVA, respectively) are also seen.

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Fig. 2D —1-week-old female neonate with type A interrupted aortic arch, ventricular septal defect, and patent ductus arteriosus. Large patent ductus arteriosus (PDA) arises from left pulmonary artery (LPA).

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Fig. 2E —1-week-old female neonate with type A interrupted aortic arch, ventricular septal defect, and patent ductus arteriosus. Patent ductus arteriosus (PDA) provides blood flow to right descending thoracic aorta (DA).

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Fig. 2F —1-week-old female neonate with type A interrupted aortic arch, ventricular septal defect, and patent ductus arteriosus. Maximum-intensity-projection image also shows site of aortic arch interruption (INT).

Another relatively specific imaging finding for IAA is visualization of a single complete thoracic vascular arch on a single sagittal image (resembling a “normal” aortic arch) (Figs. 3A, 3B, 3C, 3D, 4A, 4B, 4C and 4D). As a rule, the aortic arch cannot be seen in its entirety on a single sagittal image because the vessel typically courses within the thorax from anterior and right to posterior and left. In patients with IAA, the patent ductus arteriosus may mimic a “normal” aortic arch. This structure is oriented in an anteroposterior direction, and it is best seen on sagittal imaging communicating between the pulmonary artery and aorta. Consequently, sagittal MRI can be misleading if not reviewed carefully and may erroneously suggest the presence of an intact aortic arch in the setting of interruption. A visualized patent ductus arteriosus typically lacks the classic morphologic appearance of a normal aortic arch; instead it appears somewhat flat (Figs. 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, 5A, 5B and 5C).

Additional MRI findings can also be observed in the setting of IAA. The great vessels may show a V configuration on coronal imaging (Figs. 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, and 6A, 6B, 6C, 6D). The ascending thoracic aorta may be smaller in caliber than expected due to decreased blood flow (Figs. 2A, 2B, 2C, 2D, 2E, 2F, 6A, 6B, 6C and 6D). Also, note that a right aortic arch with a left descending thoracic aorta and hypo plastic retroesophageal segment may mimic the appearance of IAA [19] (Figs. 7A and 7B). MRI should be used to distinguish this entity from IAA because surgical correction may differ. Rarely, a form of IAA may be encountered that does not fit the exact criteria for any of the three described types (Figs. 5A, 5B, 5C, 6A, 6B, 6C and 6D).

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Fig. 3A —1-week-old male neonate with type B interrupted aortic arch (IAA) and ventricular septal defect. Coronal double inversion recovery fast spin-echo black blood MR image reveals normal ascending aorta (AA) arising from left ventricle. Main pulmonary artery (MPA) and ventricular septal defect (VSD) are also visualized.

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Fig. 3B —1-week-old male neonate with type B interrupted aortic arch (IAA) and ventricular septal defect. MR image shows right and left common carotid arteries (RCCA and LCCA, respectively) arise from proximal aortic arch.

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Fig. 3C —1-week-old male neonate with type B interrupted aortic arch (IAA) and ventricular septal defect. Slightly more posterior within thorax, patent ductus arteriosus (PDA) arises from left pulmonary artery (LPA). Right pulmonary artery (RPA) and left atrium (LA) are also seen at this level.

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Fig. 3D —1-week-old male neonate with type B interrupted aortic arch (IAA) and ventricular septal defect. Sagittal black blood MR image shows vascular arch that is almost completely visualized in single sagittal plane. This structure is formed from main pulmonary artery (MPA) and patent ductus arteriosus (PDA) and appears flattened compared with normal aortic arch, confirming presence of IAA. Patent ductus arteriosus provides blood flow to descending thoracic aorta (DA). Left pulmonary artery (LPA) is also seen.

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Fig. 4A —3-day-old male neonate with type B interrupted aortic arch, large aortopulmonary window, and pulmonary sling. Coronal gradient-recalled echo “white blood” MR image shows abnormal communication between ascending aorta (AA) and main pulmonary artery (MPA), so-called aortopulmonary window (APW).

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Fig. 4B —3-day-old male neonate with type B interrupted aortic arch, large aortopulmonary window, and pulmonary sling. MR image shows innominate artery (IA) and left common carotid artery (LCCA) arising from proximal aortic arch in V configuration.

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Fig. 4C —3-day-old male neonate with type B interrupted aortic arch, large aortopulmonary window, and pulmonary sling. MR image shows that left pulmonary artery (LPA) arises from right pulmonary artery (RPA) at level of left atrium (LA), confirming presence of pulmonary sling. Patent ductus arteriosus (PDA) provides blood flow to descending thoracic aorta (DA).

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Fig. 4D —3-day-old male neonate with type B interrupted aortic arch, large aortopulmonary window, and pulmonary sling. Sagittal gradient recalled-echo white blood MR image shows complete vascular arch in single sagittal plane is formed from pulmonary artery and patent ductus arteriosus (PDA). DA = descending thoracic aorta.

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Fig. 5A —4-day-old female neonate with DiGeorge syndrome, type 2 truncus arteriosus, surgically confirmed interrupted aortic arch, postductal origins of left carotid and left subclavian arteries, and aberrant retroesophageal right innominate arteries. Sagittal oblique subvolume maximum-intensity-projection (MIP) gadolinium-enhanced 3D MR angiography image reveals that ascending aorta and main pulmonary artery arise from single outflow tract, consistent with truncus arteriosus (TA). Patent ductus arteriosus (PDA) directly communicates with descending thoracic aorta (DA). Both right and left common carotid arteries (RCCA and LCCA, respectively) arise from postductal aorta. This interrupted aortic arch branching pattern does not fit criteria for any of the three previously described types. Normal aortic arch is not seen.

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Fig. 5B —4-day-old female neonate with DiGeorge syndrome, type 2 truncus arteriosus, surgically confirmed interrupted aortic arch, postductal origins of left carotid and left subclavian arteries, and aberrant retroesophageal right innominate arteries. Subvolume MIP image in sagittal obliquity slightly different from A confirms that right and left pulmonary arteries (RPA and LPA, respectively) arise separately from common trunk, consistent with type 2 truncus arteriosus (TA). Origin of patent ductus arteriosus (PDA) is also seen. DA = descending thoracic aorta.

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Fig. 5C —4-day-old female neonate with DiGeorge syndrome, type 2 truncus arteriosus, surgically confirmed interrupted aortic arch, postductal origins of left carotid and left subclavian arteries, and aberrant retroesophageal right innominate arteries. Axial subvolume MIP image confirms postductal aberrant retroesophageal innominate artery (IA) gives rise to right common carotid and right subclavian arteries. PDA = patent ductus arteriosus, TA = truncus arteriosus.

Prognosis and Treatment	Choose Top of pageABSTRACTIntroductionTypes of Interrupted Aort...Pathogenesis and Associat...Imaging of Interrupted Ao...Prognosis and Treatment <<ConclusionsReferencesCITING ARTICLES

IAA is associated with a mortality rate of more than 90% at 1 year of age if untreated [4]. Mean patient survival is approximately 4-10 days [20]. Death is typically due to a combination of increasing left-to-right shunt, ventricular failure, and ductus arteriosus closure. Closure of the ductus arteriosus results in hypoperfusion-related complications, including renal failure and metabolic acidosis [1]. Rarely, patients with IAA can present in adulthood due to the presence of unusual collateral vessels [1, 21, 22].

The initial treatment of IAA is IV prostaglandin therapy to preserve ductus arteriosus patency and blood flow beyond the interruption. Surgical correction is then performed after appropriate imaging evaluation and operative planning. Multiple surgical reparative techniques are available, including both one-stage and multistage procedures. A one-stage repair includes direct aortic arch primary anastomosis (either end-to-end or end-to-side) with or without placement of synthetic graft material across the defect and possible ventricular septal defect repair. A multistage procedure is often considered in the setting of IAA and associated complex congenital heart disease. The initial stage typically involves aortic arch reconstruction and pulmonary artery banding in the presence of a ventricular septal defect. At least one more surgery is then required to remove the pulmonary artery band and repair additional cardiac defects [23-25].

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Fig. 6A —3-day-old female neonate with interrupted aortic arch, aberrant left subclavian artery from left patent ductus arteriosus, aberrant right subclavian artery from descending thoracic aorta, and right descending thoracic aorta. Gadolinium-enhanced 3D MR angiography images show small-caliber ascending aorta (AA in A) arising from left ventricle. Right and left common carotid arteries (RCCA and LCCA, respectively) form V configuration.

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Fig. 6B —3-day-old female neonate with interrupted aortic arch, aberrant left subclavian artery from left patent ductus arteriosus, aberrant right subclavian artery from descending thoracic aorta, and right descending thoracic aorta. Gadolinium-enhanced 3D MR angiography images show small-caliber ascending aorta (AA in A) arising from left ventricle. Right and left common carotid arteries (RCCA and LCCA, respectively) form V configuration.

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Fig. 6C —3-day-old female neonate with interrupted aortic arch, aberrant left subclavian artery from left patent ductus arteriosus, aberrant right subclavian artery from descending thoracic aorta, and right descending thoracic aorta. Coronal oblique subvolume maximum-intensity-projection (MIP) and volume-rendered images confirm presence of interrupted aortic arch. Right patent ductus arteriosus (RPDA) supplies blood flow to descending thoracic aorta (DA). Left subclavian artery (LSCLA) arises from small left patent ductus arteriosus (LPDA), and right subclavian artery (RSCLA) arises from postductal descending thoracic aorta. This interrupted aortic arch branching pattern does not fit criteria for any of the three previously described types. MPA = main pulmonary artery; in C, RPA = right pulmonary artery; in D, AA = ascending aorta, RCCA = right common carotid artery, LCCA = left common carotid artery.

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Fig. 6D —3-day-old female neonate with interrupted aortic arch, aberrant left subclavian artery from left patent ductus arteriosus, aberrant right subclavian artery from descending thoracic aorta, and right descending thoracic aorta. Coronal oblique subvolume maximum-intensity-projection (MIP) and volume-rendered images confirm presence of interrupted aortic arch. Right patent ductus arteriosus (RPDA) supplies blood flow to descending thoracic aorta (DA). Left subclavian artery (LSCLA) arises from small left patent ductus arteriosus (LPDA), and right subclavian artery (RSCLA) arises from postductal descending thoracic aorta. This interrupted aortic arch branching pattern does not fit criteria for any of the three previously described types. MPA = main pulmonary artery; in C, RPA = right pulmonary artery; in D, AA = ascending aorta, RCCA = right common carotid artery, LCCA = left common carotid artery.

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Fig. 7A —2-day-old female neonate with Down syndrome, right aortic arch with left descending thoracic aorta and hypoplastic retroesophageal segment, ventricular septal defect, and bilateral superior venae cavae. Coronal maximum-intensity-projection gadolinium-enhanced 3D MR angiography image shows apparent interruption (INT) of aortic arch between left common carotid artery (LCCA) and left subclavian artery (LSCLA). Right pulmonary artery (RPA) is seen. PDA = patent ductus arteriosus, DA = descending thoracic aorta.

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Fig. 7B —2-day-old female neonate with Down syndrome, right aortic arch with left descending thoracic aorta and hypoplastic retroesophageal segment, ventricular septal defect, and bilateral superior venae cavae. Volume-rendered image confirms presence of hypoplastic retroesophageal aortic segment (REA) on closer inspection. Patent ductus arteriosus (PDA) also supplies blood flow to descending thoracic aorta (DA). MPA = main pulmonary artery.

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Fig. 8 —21-year-old man with history of type A interrupted aortic arch (IAA) being evaluated following surgical repair. Sagittal maximum-intensity-projection (MIP) gadolinium-enhanced 3D MR angiography image shows vertically oriented ascending aorta (A) giving rise to origins of all great vessels (arrow). Synthetic patch is seen bridging area of aortic arch interruption and supplies blood flow to descending aorta (DA). Main pulmonary artery (PA) is also seen.

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Fig. 9A —14-year-old boy with history of type A interrupted aortic arch (IAA) being evaluated for status after repair of IAA. Synthetic graft material was used to bridge interrupted portion of aortic arch. Axial double inversion recovery fast spin-echo black blood MR image reveals area of proximal anastomotic narrowing (arrow).

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Fig. 9B —14-year-old boy with history of type A interrupted aortic arch (IAA) being evaluated for status after repair of IAA. Synthetic graft material was used to bridge interrupted portion of aortic arch. Sagittal oblique 2D balanced steady-state free precession image shows that ascending aorta (A) is not dilated proximally. Finding seen in A (arrow) is confirmed.

After surgical correction, estimates of early mortality rates have ranged from less than 8% to 37% [6, 23, 24]. Long-term survival has increased over the past 3 decades and now approaches 92% 1 year after surgical repair [6, 24]. Because patients with IAA are living longer, MRI is particularly useful in the postoperative setting to detect complications such as anastomotic narrowing and graft aneurysms (Figs. 8, 9A and 9B). MRI is invaluable in the evaluation of older children and adults with repaired IAA because suitable echocardiography windows may not be available to evaluate the aortic arch and great vessels.

Conclusions	Choose Top of pageABSTRACTIntroductionTypes of Interrupted Aort...Pathogenesis and Associat...Imaging of Interrupted Ao...Prognosis and TreatmentConclusions <<ReferencesCITING ARTICLES

IAA is a rare form of congenital vascular anomaly. Although echocardiography is more commonly used to evaluate this condition, MRI can play a complementary role because of its ability to accurately define aortic and cardiac anatomy. MRI can be used to identify the site and length of aortic arch interruption, the origins of the great vessels, and associated congenital cardiac defects. MRI may be particularly beneficial in the workup of suspected IAA when the defect cannot be adequately evaluated by echocardiography and in the postoperative setting.