Interrupted aortic arch (IAA) is an extremely serious condition of the heart in which the development of the aortic arch is disrupted.
The arch of the aorta is the segment which connects the ascending and descending parts of this great artery, which carries oxygenated blood from the left ventricle of the heart to the entire systemic circulation.
In most cases the infant also has a ventricular septal defect (VSD) or an atrial septal defect (ASD).
Many other genetic conditions are also associated with IAA, such as the DiGeorge syndrome, especially in type B, which is due to the same chromosomal deletion in both cases.
Trisomy 13 and 18 have also been found to occur alongside IAA.
Other associations include:
- Truncus arteriosus, where a single vessel arises from both the ventricles
- Aortopulmonary window, where there is a defect in the septum between the aorta and the pulmonary artery
- Transposition of the great arteries (pulmonary artery and aorta)
- Double-outlet right ventricle
- Functional single ventricle defects
Normal Heart Functioning
In the normal functioning heart, the left side of the heart receives blood following oxygenation in the lungs, via the pulmonary arteries which empty into the left atrium.
This passes through the mitral valve to reach the left ventricle, from where it is pumped out into the aorta to supply the whole body.
The upper part of the body, namely, the head, neck and upper limbs, are supplied through the branches of the aorta that arise from the aortic arch. These comprise:
- The right brachiocephalic artery which divides into the right common carotid and right subclavian arteries, supplying the head and right upper limb respectively.
- The left common carotid artery
- The left subclavian artery
- The descending aorta branches off to the rest of the body.
Returning venous blood drains into the right side of the heart, namely, the right atrium, through the great veins, the superior and inferior vena cavae.
This blood empties into the right ventricle through the tricuspid valve, from where it is pumped to the lungs for oxygenation through the pulmonary trunk.
Blood from the lungs returns to the left atrium and the cycle is repeated. Both sides of the heart are thus separated from each other throughout their functioning.
During fetal life, the ductus arteriosus connects the pulmonary artery to the aorta, to bypass the pulmonary circulation. This vessel closes in the first few days after birth.
Abnormal Circulatory Function in IAA
In an infant with IAA, the missing aortic arch means that oxygenated blood from the left ventricle cannot reach the descending aorta and supply the body below the level of the subclavian arteries.
The presence of the ductus arteriosus allows some desaturated or hypoxemic blood to be shunted into the aorta below the level of the ductus, and this reaches the lower part of the body. The upper part of the body receives oxygen-rich blood, however.
When a VSD is present, some oxygenated blood from the left ventricle reaches the right ventricle and is pumped into the pulmonary artery. This will ensure that some oxygen reaches the lower body through the ductus. Thus the presence of right-to-left shunts at various levels helps the infant with IAA to compensate for the lack of the aortic arch to a small extent. However, these babies are usually very sick at birth. The closure of the ductus precipitates cardiogenic shock and metabolic acidosis.
Surgical correction following emergency stabilization of the infant is the only possible treatment that can offer a chance of survival.
One-stage or multiple-stage repairs have been carried out. At present most surgeons prefer a one-stage repair with primary repair of the aortic arch.
The advantages of a one-stage repair include:
- The need for fewer reoperations
- Avoiding the need of pulmonary artery banding which increase the rate of development of subaortic stenosis, an independent risk factor for death
- Possible avoidance of future reconstructions of the aortic arch
Staged repair can use the left carotid artery as an autograft to fuse the two segments of the aorta, or employ synthetic grafts.
The use of the native left carotid artery was not associated with any short-term or future neurodevelopmental or other adverse outcomes.
Complications following aortic arch reconstruction include:
- Bronchial compression when the anastomosis of the ascending and descending aorta produces too much tension on the two components
- Aortic arch stenosis recurring after some time requiring reoperation
- Left ventricular outflow tract obstruction
Factors which increase the mortality odds include:
- Low birth weight
- Repair at younger ages
- Type B IAA
- VSDs which involve the ventricular outlet or trabeculae
- Small VSDs
- Subaortic stenosis
In some centers, the mortality at 10 years is 19% after staged correction, which reflects a dramatic improvement over the decades since the development of corrective surgery for this condition. However, reoperation rates remain high at present.