Interrupted aortic arch

Interruption of the aortic arch (IAA) is characterized by a complete separation of the ascending and descending aorta^1-3

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Three anatomical types have been described according to the site of interruption: in Type A the interruption is distal to the left subclavian artery; in Type B it is between the left carotid and left subclavian arteries; and in Type C it is between the innominate artery and the left carotid artery.^1-3 IAA Type A is rarely associated with 22q11.2 deletion, whereas Type B is associated with this and other extracardiac features in more than 50% of cases, often in the context of specific syndromes.^4-7 Type C is by far the least common form of IAA, accounting for fewer than 5% of cases. A ventricular septal defect is typically found in most cases of IAA, especially type B.

It has been suggested that the etiology of IAA type B is distinct from both of the other forms of IAA.^{4,5, 8}  The pathogenetics of IAA type A are believed to be more closely related to CoA and are thought to be caused by abnormal blood flow during embryogenesis.^{4, 8}  On the other hand, IAA type B is caused by an abnormality of neural crest cell migration.^4-6  Interrupted aortic arch does not cause cardiac compromise during intrauterine life.

A large malalignment-type ventricular septal defect is almost always associated with IAA type B5. An aberrant right or left subclavian artery and a right aortic arch are associated in about one third of IAA type B cases. Extracardiac malformations primarily involve the 22q11 microdeletion9, which is associated with IAA type B in about 50% of cases whereas type A is rarely associated with 22q11 microdeletion.^3-7  Extracardiac malformations, not related to 22q11 microdeletion, found in IAA include holoprosencephaly, esophageal atresia, duplicated stomach and diaphragmatic hernia.

In IAA type A, a pronounced asymmetry of the ventricles is evident on the four-chamber view, with the left ventricle being much smaller than the right. Conversely, in type B the size of the left ventricle is usually normal. In all IAA types, a pronounced discrepancy in diameter of the great vessel is present, with the AAo being much smaller than the main pulmonary artery.

The three-vessel and trachea view is the reference plane for diagnosing IAA.^{3, 5,10} In fact, in the three-vessel-trachea view the continuity of the transverse aortic arch toward the descending aorta cannot be demonstrate. As for coarctation of the aortic arch, care must be taken on the longitudinal view not to mistake the prevalent ductal arch for a normal aortic arch.

With regard to US differentiation of the various subtypes, type B can be difficult to distinguish from type A. In type B, the ascending aorta has a straighter course to the innominate and left carotid arteries, the typical “V” shape, whereas in type A, there is a slight curvature after the origin of the innominate artery related to the persistence of the aortic arch segment between the origin of the left carotid and subclavian arteries ( the typical “W” shape)^4,5. An infundibular malalignment VSD with a leftward and posterior displacement of the infundibular septum is typically found in vast majority of IAA type B.

The use of color Doppler may facilitate assessment of the continuity (or absence there of) of the ascending aorta with the descending part; it also facilitates assessment of the course of the ascending aorta and neck vessels. Spectral Doppler is of limited use, while 4D echocardiography has been demonstrated to facilitate the assessment of aortic arch anomalies, especially with B-flow.⁵

The surgical management of IAA is controversial. Primary anastomosis and patch aortoplasties combined with end-to-end anastomosis have significant complications, including recurrence and aneurysm formation. Pulmonary autograft patch aortoplasty together with end-to-side anastomosis comprise an alternative approach to surgical management and do not require cardiopulmonary bypass. In a large case series, preoperative death occurred in 5% of cases, and the survival rate at four years after repair was 73%.^{2, 11} 

Risk factors for post-interventional death are low birth weight and major associated cardiac anomalies. The discrepancies among the clinical features and, above all, the remarkable difference with regard to association with the 22q11 microdeletion suggest that type A and type B IAA could be two separate pathogenetic entities, with the latter type carrying a poorer prognosis.

Should IAA be detected in a fetus, a thorough anatomic scan should be carried out by an expert to detect possible additional anomalies, such as thymus hypoplasia, which increase the risk of 22q11 microdeletion even more. Fetal karyotyping with FISH analysis for the 22q11 microdeletion is indicated in type B IAA. Timing and mode of delivery are unchanged, but the delivery should be planned in a tertiary referral center in order to reach a definite diagnosis and to adequately manage the situation in the neonatal period search for associated anomalies including fetal karyotype and diagnosis of microdeletion 22q11. In continuing pregnancies, the lesion is usually well tolerated by the fetus and does not alter standard obstetric management.

1.Collins-Nakai RL, Dick M, Parisi-Buckley L, Fyler DC, Castaneda AR. Interrupted aortic arch in infancy. J Pediatr. 1976;88(6):959-62.

2. Brierley J, Redington AN. Aortic coarctation and interrupted aortic arch. In Pediatric Cardiology, Anderson RH, Macartney FJ, Shinebourne EA, Tynan M (eds). Churchill Livingstone: Edinburgh, UK, 2001

3. Abuhamad A, Chaoui R . Coarctation of the aorta and interrupted aortic arch. In A practical guide to fetal echocardiography, Abuhamad A, Chaoui R. (eds). Lippincot Williams & Wilkins 2010

4. Volpe P, Marasini M, Caruso G, Gentile M. Prenatal diagnosis of interruption of the aortic arch and its association with deletion of chromosome 22q11. Ultrasound Obstet Gynecol 2002;20:327–331S,

5. Volpe P, Tuo G, De Robertis V, Campobasso G, Marasini M, Tempesta A, Gentile M, Rembouskos G. Fetal interrupted aortic arch: 2D-4D echocardiography, associations and outcome. Ultrasound Obstet Gynecol. 2010;35:302-9.

6. Goldmuntz E, Clark BJ, Mitchell LE, Jawad AF, Cuneo BF, Reed L, McDonald-McGinn D, Chien P, Feuer J, Zachai EH, Emanuel BS, Driscoll DA. Frequency of 22q11 deletions in patients with conotruncal defects. J Am Coll Cardiol 1998; 32: 492–498

7. Volpe P, Gentile M, Marasini M. Interrupted aortic arch type A with 22q11 deletion: prenatal detection of an unusual association. Prenat Diagn. 2002;22(5):371-4.

8. Van Mierop LH, Kutsche LM. Interruption of the aortic arch and coarctation of the aorta: Pathogenetic relations. Am J Cardiol 1984;54: 829–834.

9. Volpe P, Marasini M, Caruso G, Marzullo A, Buonadonna AL, Arciprete P, Di Paolo Volpe G, Gentile M. 22q11 deletions in fetuses with malformations of the outflow tracts or interruption of the aortic arch: impact of additional ultrasound signs. Prenat Diagn. 2003 .

10. Gardiner H, Chaoui R. The fetal three-vessel and tracheal view revisited. Seminars in fetal & neonatal medicine. 2013 Oct;18(5):261-8. .

11. Paladini D, Volpe P. Interrupted aortic arch. In Ultrasound of congenital fetal anomalies (eds Paladini D, Volpe P). CRC Press. 2014

Volpe P., Pilu G. Interrupted aortic arch. VISUOG, 17 June 2014

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