Tuesday, February 7, 2023

Interrupted Aortic Arch

Background

Interrupted aortic arch (IAA) is a relatively rare genetic disorder that usually occurs in association with a nonrestrictive ventricular septal defect (VSD) and ductus arteriosus or, less commonly, with a large aortopulmonary window or truncus arteriosus.
 Although most cases occur in normally connected great arteries, interrupted aortic arch can coexist with any ventriculoarterial alignment and also with severe underdevelopment of one ventricle. The rare cases that involved interrupted aortic arch, aortic valve atresia, and VSD have been complex; two have presented with circle of Willis–dependent coronary blood flow,
and two have presented with bilateral ductus in which coronary blood flow depended on the patency of the right ductus arteriosus.
 

Interrupted aortic arch and complete common atrioventricular canal can be observed in the context of coloboma, heart disease, atresia choanae, retarded growth and development and/or CNS anomalies, genital hypoplasia, and ear anomalies and/or deafness (CHARGE) syndrome, which is usually caused by mutations in CHD7 on chromosome 8q12.1.
Approximately 50% of patients with interrupted aortic arch have DiGeorge syndrome; in these cases, the interrupted aortic arch is usually type B, although cases of type A or type C have also been reported. There is considerable phenotypic overlap between CHARGE and DiGeorge syndromes.

Surgical reconstruction of the arch is now relatively straightforward; hence, attention is increasingly focused on the preoperative identification and surgical management of the aortic valve and subaortic stenosis found in approximately one half of cases.
Interrupted aortic arch is the first cardiovascular pattern formation anomaly to be demonstrated to have a genetic basis in both mouse and human.

Embryology

Approximately one half of patients with interrupted aortic arch have a hemizygous deletion of a 1.5-3 Mb region of chromosome band 22q11.2,
the most common deletion syndrome in humans. Among the 35-50 genes deleted, the T-box gene TBX1 appears to be responsible for most aspects of the DiGeorge phenotype.

In addition, 2 independent lines of evidence suggest that the etiology of many cases of interrupted aortic arch type A is different from the etiology of interrupted aortic arch type B (see below for definition of types). The variety of associated VSDs is different in the 2 types of interrupted aortic arch.
The prevalence of 22q11.2 hemizygosity is also different; approximately three fourths of patients with interrupted aortic arch type B have the deletion, whereas exceedingly few patients with interrupted aortic arch type A have the deletion.

Anatomy

Interrupted aortic arch has been classified into 3 types (A, B, and C) based on the site of aortic interruption. In type A interrupted left aortic arch, the arch interruption occurs distal to the origin of the left subclavian artery. In type B interrupted left aortic arch, the interruption occurs distal to the origin of the left common carotid artery. In type C interrupted left aortic arch, the interruption occurs proximal to the origin of the left common carotid artery.

In any of the 3 types, the right subclavian artery may arise normally or abnormally; the 2 most common abnormal sites are distal to the left subclavian artery (aberrant right subclavian artery) and from a right ductus arteriosus (isolated right subclavian artery).
Type B interruptions account for about two thirds of cases, type A occur in about one third of cases, and type C are present in less than 1% of cases.

Suprasternal echocardiographic identification of i

Suprasternal echocardiographic identification of interrupted aortic arch Type B. Upper left: Frontal (coronal) view showing the takeoffs of the innominate artery (InnA) and left common carotid artery (LCCA). No connection is seen with the distal aorta. Upper right: Slightly more dorsal (posterior) frontal view showing the main pulmonary artery (MPA), large left-sided patent ductus arteriosus (PDA), and left-sided upper descending aorta (DescAo). The ascending aorta (AscAo) is not in discernible continuity with the descending aorta. Lower left: Left oblique view showing the LCCA takeoff and no discernible aortic arch. Lower right: sagittal view showing the origin of the left subclavian artery (LSCA) from the DescAo. Other Abbreviations: InnV= innominate vein; l=left; LPA=left pulmonary artery; p,l = posterior and leftward; s=superior; SVC=superior vena cava.

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Section A depicts a subcostal frontal echocardiogr

Section A depicts a subcostal frontal echocardiogram of interrupted aortic arch (IAA) type B with transposition of the great arteries. Section B shows a high parasternal echocardiogram showing that the innominate artery (Inn A) and left common carotid artery (LCCA) arise from the ascending aorta (a ao). In section C, the left subclavian artery (LSCA) arises from the descending aorta (desc ao), which is perfused by the ductus arteriosus.

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This is the suprasternal sagittal ultrasonographic

This is the suprasternal sagittal ultrasonographic view of the patient shown in Media file 2. Arch continuity has now been restored by a side-to-side anastomosis. Abbreviations are as follows: a ao = ascending aorta and desc ao = descending aorta.

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