Discussion and Conclusion:
Interrupted aortic arch (IAA) is caused by a complete interruption of aortic lumen between the ascending and descending aorta. It is a rare and complicated congenital cardiovascular condition with high mortality in infants. Approximately 75% of patients with IAA died by 10 days after birth and 90% died within the first year after birth2. Steidele, et al. reported the first case of IAA in 1778 7 and the the first surgical correction of IAA was performed by Samson in 1955 8.
Based on the position of the interruption, IAA can be clinically categorized into 3 types(1). Type A(40%): the aortic arch interruption is at the distal end of the left subclavian artery. Type B(55-60%): the interruption is between the left subclavian artery and the left common carotid artery and strongly associated with DiGeorge syndrome and chromosome 22q11.2 deletion 9,10. Type C(4%): The interruption is between the innominate artery and left common carotid artery. Patients with Type A IAA are more likely to have adequate collateral flow and thus are commonly asymptomatic. Type B and C IAA have disparate upper extremity pressures making diagnosis in childhood and adolescence more common. Based on associated additional deformities, they can be further classified as complex and isolated types. Complex types are common and usually occurs with other cardiac malformations like patent ductus arteriosus (PDA), aortopulmonary window, ventricular septal defect (VSD), etc. 3,4. These malformations can guarantee the blood supply of descending aorta. Isolated type is very rare 11.
Because IAA always combines with PDA and VSD, some newborns seldom have overt heart symptoms in early weeks after birth. However, at a later phase of the infancy, the decreasing of pulmonary vascular resistance and increased left to right shunt can cause congestive heart failure. In many cases, the ductus arteriosus begins to close shortly after birth. If the ductus arteriosus closes too rapidly, the collateral circulation between the ascending and descending aortas is not well developed. Consequently poor perfusion of the lower part of the body can lead to ischemia of splanchnic organs, severe acidosis, and anuria4,7. Therefore, it is rare for patients with isolated IAA to survive to adulthood without surgical intervention unless the extensive collateral vessels joining the descending aorta are established 11.
Most of patients with isolated IAA in adulthood come to hospital with the complaint of hypertension 12. Other common symptoms include claudication and congestive heart failure13-15. It is difficult to identify such patients unless discrepancy between the blood pressure of the upper and lower extremities is found or echocardiography is performed. The pulsation of lower or up extremity artery may be helpful but it depends on the position of the interruption.
Echocardiography is a useful initial screening method, particularly important for neonates, to identify and measure necessary anatomical data of IAA, and identify other cardiac malformations2,16. CTA provides a high resolution 3-dimensional image of IAA and collateral vessels 12,17,18. The combination of echocardiography and CTA is usually recommended for a definitive diagnosis 9. Although aortography can demonstrate complete occlusion of the aorta and the position of the interruption, it is usually not the first choice due to its invasive procedure. Nevertheless, an aortography is necessary when CTA can not distinguish between aortic arch interruption and coarctation.
The main treatment for IAA in neonates and infants is surgical intervention 15,19. There is a growing preference for a radical surgery which includes a reconstruction of aortic arch continuity and repair of cardiac malformations under deep hypothermic circulatory arrest in a single-staged procedure. Several surgical means, such as end-to-end or end-to-side anastomosis can be used15. For neonates and infants, blood can flow through the artery catheter into the descending aorta. Before operation, prostaglandin E can be used intravenously, with endotracheal intubation and mechanical ventilation support. High tidal volume and high concentration of oxygen supply should be avoided since they may cause respiratory alkalosis.
The main treatment for IAA in adults is the same with in neonates or infants. About 90% of patients prefer a surgical correction. Either sternotomy or thoracotomy seems reasonable depending on the size and location of collaterals. However, end-to-end or end-to-side anastomosis is less common in adults than the extra-anatomic bypass20,21. When collateral circulation is abundant, surgery can be difficult due to high bleeding risk 21. Krishna et al. reported one case that one patient received subclavian to descending aorta bypass required surgical re-exploration 3 times for bleeding from ruptured collaterals 22. Freedman H K et al first proposed the theory that some type A IAA may be the result of regression or atrophy of a previously existing segment of aortic arch between the ductus arteriosus and left subclavian artery comparable with coarctation of the aorta as this segment can be narrowed, atretic, and replaced by a fibrous band, or completely absent23. Kusa et al. cautioned that the percutaneous stent placement was possible in those patients. He also cautioned that immediate access to cardiac surgery must be available in case of an emergency 7,14.
In most of reported cases, patients’ symptoms intend to improve after surgery. Hypertension gradually resolves after surgery, and anti-hypertensive management can be discontinued. Other symptoms such as claudication and paresthesia are also ameliorated after surgery9,24. However C. Sai Krishna et al reported that among seven patients received operation, five patients still had residual mild hypertension that was well-controlled with anti-hypertensive management 21. Similarly in our case 3, the patient’s blood pressure remained high after the surgery. Considering that IAA is similar to coarctation of the aorta (CoA) , we reviewed the relevant data of CoA and found that 68% of patients still have hypertension after surgery. This lack of blood pressure improvement may be related to abnormal geometry of the aortic arch or hypoplasia of the arch changes in arterial function, hyperactivation of the renin angiotensin system, and attenuation of baroreflexes24. So for patients with abundant collateral and no symptoms of ischemia of splanchnic organs and lower limbs, anti-hypertensive management without surgical intervention is reasonable. Nonetheless, close follow-up and further study is necessary.
Although it is extremely uncommon, IAA must be considered in the diagnosis of an adult patient with severe hypertension. For adult patients with isolated IAA and no symptoms besides hypertension, it likely that their collateral circulation is sufficient. For such patients, surgical intervention may not be the best option,while anti-hypertensives management appears to be adequate and safe.