Case of Interrupted Aortic Arch type B

Summary

Interrupted aortic arch is a rare and critical congenital heart defect characterized by a complete lack of luminal continuity between the ascending and descending segments of the aorta. This anomaly is anatomically categorized into three types based on the site of the discontinuity. Type A occurs when the interruption is located distal to the origin of the left subclavian artery, representing about twenty-eight percent of cases. Type B, which is the most frequently encountered variant, involves an interruption between the left common carotid and left subclavian arteries. The rarest form is Type C, where the discontinuity is positioned between the innominate and left common carotid arteries. This defect is almost invariably associated with other cardiac anomalies, most notably a large ventricular septal defect, which is present in over ninety percent of patients. When a ventricular septal defect is absent, a significant alternative shunt such as an aortopulmonary window is typically found to allow for survival. Furthermore, Type B interruptions carry a strong clinical association with DiGeorge syndrome, occurring in approximately half of those patients. These individuals should be screened for the 22q11 microdeletion, which often manifests with additional findings like thymic hypoplasia and hypocalcemia. The embryological basis for these defects is believed to involve abnormal development or regression of specific segments within the embryonic branchial arterial system. Interrupted aortic arch represents the most severe end of the spectrum of aortic arch obstruction and differs from critical coarctation by the complete absence of luminal continuity between the ascending and descending aorta. The right ventricle typically becomes the dominant systemic ventricle, supplying the descending aorta through the patent ductus arteriosus, whereas the left ventricle primarily supports the ascending aorta and cerebral circulation. Echocardiography demonstrates discontinuity of the aortic arch, absence of antegrade flow into the descending aorta, and ductal-dependent perfusion of the lower body. Doppler interrogation often reveals retrograde flow within the descending thoracic aorta supplied through the ductus arteriosus. Left ventricular outflow tract abnormalities, including a hypoplastic aortic valve, subaortic narrowing, or posterior malalignment of the conal septum, are common and may influence surgical planning and long-term outcomes.

During fetal life, the circulation is typically maintained by the right ventricle providing blood to the lower body through the ductus arteriosus. Prenatal diagnosis remains challenging because ductal flow bypasses the interruption in utero. Suspicion should arise when there is ventricular disproportion, a small aortic arch, or evidence of evolving left-sided obstruction. Prenatal recognition allows planned delivery at a tertiary cardiac center and avoidance of circulatory collapse following ductal closure. 

After birth, the infant becomes entirely dependent on the patency of this ductal channel for systemic perfusion to the descending aorta. As the ductus begins to naturally constrict, the infant will rapidly deteriorate, presenting with poor feeding, weak or absent femoral pulses, and profound metabolic acidosis (due to lower body ischemia). A hallmark clinical finding is differential oxygen saturation, where saturations in the right arm are higher than those measured in the lower extremities. A significant upper-to-lower extremity blood pressure gradient, diminished or absent femoral pulses, and differential perfusion are often striking findings, particularly in the early stages of ductal constriction.

Without urgent medical stabilization, the condition has high mortality, with seventy-five percent of untreated patients dying within one month of birth. Initial management centers on the immediate administration of prostaglandin E1 to maintain ductal patency and ensure adequate systemic blood flow. Once the infant is stabilized and metabolic imbalances are corrected, definitive surgical repair is required, typically performed as a single-stage reconstruction during the first week of life. This surgery involves reconstructing the aortic arch and closing the associated ventricular septal defect. While contemporary surgical outcomes have improved significantly, these patients require lifelong cardiac surveillance. Long-term complications may include recurrent obstruction at the site of the aortic repair or the development of subaortic stenosis, often resulting from the posterior displacement of the conal septum.

Anatomic and Genetic Nuances

• Rarely, Interrupted aortic arch (IAA) can exist without a ventricular septal defect (VSD), although this is rare, as a VSD is present in nearly all patients (over 90% of cases). In cases where a VSD is not present, there is almost always another significant intracardiac or extracardiac shunt. An aortopulmonary (AP) window is the most common alternative shunt found when the ventricular septum is intact. 

• Berry Syndrome: This is a specific, rare combination of cardiovascular anomalies that includes IAA (usually Type A), a distal AP window, and an intact ventricular septum, along with the origin of the right pulmonary artery from the ascending aorta. 

• Isolated IAA: There are occasional reports of IAA occurring as an isolated lesion. In these extremely rare instances, the arterial duct (PDA) is closed, and systemic flow to the descending aorta is maintained through profuse collateral arteries that develop between the separated aortic segments. 

• Aberrant Right Subclavian Artery: This is a common associated vascular anomaly, particularly in Type B IAA. When present, the oxygen saturation in the right arm may be the same as in the legs, which can mask the classic differential saturation sign.

• Specific VSD Morphology: The associated VSD is characteristically a posterior malalignment type. This specific malalignment of the outlet septum is what frequently encroaches upon the left ventricular outflow tract (LVOT), leading to subaortic stenosis.

• Additional arch vessel anomalies are common, including aberrant subclavian arteries, cervical arch variants, and vascular rings, all of which should be carefully delineated preoperatively.

Clinical Presentation and Hemodynamics Nuances

• Reverse Differential Saturation: In most IAA cases, saturations are higher in the right arm than the legs. However, if IAA is associated with Transposition of the Great Arteries (TGA) or a Taussig-Bing anomaly, the differential may be reversed (lower in the right arm than the legs).

• Isolated IAA and Collaterals: While rare, IAA can occur as an isolated lesion with a closed ductus. In these instances, survival into older childhood or even adulthood is possible due to the development of profuse collateral arteries between the separated segments.

• Dorsal Aortic Continuity: In Type B interruptions, the echocardiogram may show the left common carotid artery sweeping upward as a direct continuation of the ascending aorta, while the left subclavian artery is seen arising from the descending aorta/ductal arch.

• In patients with severe associated LVOT obstruction, systemic output from the left ventricle may be markedly restricted, with coronary and cerebral perfusion becoming dependent on flow through the reconstructed proximal aorta. Careful assessment of aortic valve size, LVOT dimensions, and subaortic anatomy is therefore essential during surgical planning.

Management and Surgical Strategies Nuances

• The Danger of Oxygen: Preoperatively, the administration of oxygen (FiO2) can be dangerous. Oxygen decreases pulmonary vascular resistance and constrict the ductus, both of which can worsen systemic hypoperfusion and metabolic acidosis.

• For more complex cases involving severe left ventricular outflow tract obstruction (LVOTO) or significant LVOT hypoplasia, a Yasui procedure may be required to achieve a single-stage biventricular repair. This operation is specifically indicated in neonates with interrupted aortic arch and a severely hypoplastic LVOT, typically measuring less than 4 mm in diameter or demonstrating a tunnel-like configuration that would not adequately support systemic blood flow following standard arch reconstruction. The Yasui procedure combines elements of a Norwood-type arch reconstruction and a Rastelli repair and consists of four major components: reconstruction of the aortic arch, closure of the ventricular septal defect (VSD), creation of a Damus-Kaye-Stansel (DKS) anastomosis, and placement of a valved right ventricle-to-pulmonary artery (RV-PA) conduit. Through the DKS connection, the proximal pulmonary artery is joined to the ascending aorta, while the VSD is baffled to direct left ventricular output through the pulmonary valve into the reconstructed systemic circulation, effectively bypassing the obstructed native LVOT. Pulmonary blood flow is then re-established using an extracardiac RV-PA conduit, most commonly a pulmonary homograft or bovine jugular vein (Contegra) graft. In appropriately selected patients, the Yasui procedure has demonstrated excellent survival and durable biventricular outcomes, with some series reporting results superior to those achieved with a Ross-Konno operation.

• Preoperative Recovery: It is often emphasized that surgery should not be rushed if the infant presents in shock. Management focuses on optimizing end-organ function (specifically renal and hepatic) and aggressively correcting metabolic acidosis before the infant is stable enough for cardiopulmonary bypass.

• Recurrent Laryngeal Nerve Palsy: Mentioning the risk of injury to the left recurrent laryngeal nerve during the extensive arch dissection is a standard surgical complication for these arch repairs.

• Recurrent arch obstruction is among the most frequent late complications and may require balloon angioplasty, stent placement, or surgical reintervention during childhood.

• Systemic hypertension may develop despite anatomically successful repair (possibly secondary to renal "reprogramming") and requires ongoing surveillance throughout childhood and adulthood.

Example of interrupted aortic arch type B with perimembranous ventricular septal defect

This study a very large, nonrestrictive perimembranous ventricular septal defect involving the central septum and with predominant left-to-right shunting. The aortic valve is tricuspid and demonstrates no stenosis or regurgitation; however, there is mild hypoplasia of the aortic valve annulus. Mild hypoplasia is also noted at the level of the aortic sinuses and ascending aorta. There is severe hypoplasia of the transverse aortic arch between the left common carotid and left subclavian arteries, associated with an interrupted aortic arch, type B, located between these vessels. A large patent ductus arteriosus measuring 0.60 cm is present with bidirectional shunting (predominantly right to left). Retrograde diastolic flow is observed within the descending aorta, consistent with ductal-dependent systemic circulation. Overall, biventricular systolic function is grossly preserved. The findings are most consistent with an interrupted aortic arch type B associated with a very large nonrestrictive ventricular septal defect, diffuse left heart and aortic hypoplasia, and ductal-dependent systemic blood flow.