Interrupted Aortic Arch
Interruption of the aortic arch is characterized by lack of a channel between the aortic arch and the descending aorta. The descending aorta is connected to the pulmonary arterial system by the ductus arteriosus. Classically, the ductus is left-sided, as is the descending aorta.
Variations occur in the origin of the branches of the arch. Thus, there are three types of interrupted aortic arches.
Type A encompasses about 42% of all the interrupted arches. This involves all branches arising proximal to the interruption.
Type B comprises about 53% of the interrupted arches, in which the left subclavian artery arises from the descending aorta.
Type C involves the left common carotid and left subclavian arteries arising from the descending aorta. This condition is exceedingly rare. There are other patterns involving both subclavian arteries arising from the descending aorta or just the right subclavian artery arising from the descending aorta.
Ventricular septal defect is present in over 90% of patients and our patient was no exception.
Less commonly associated anomalies include :
Ths malformation accounts for about 4% of deaths among infants with congenital heart disease in the first month of life. Without surgery the mean age of death is 4 days. There is no sex predilection.
Symptoms can include a weak or absent left subclavian arterial pulse, strong right carotid pulse. There can be differences in blood pressure and oxygen saturation.
In this diagram, one can make out the aortic arches and dorsal aortic root segments which will develop into the final aortic arch. Notice arches I and II regress. Aortic arch III will develop into the right and left common carotid arteries. Aortic arch IV becomes the aortic isthmus. The left portion of aortic arch VI becomes the PDA. The dorsal aortic roots 3-11 become the descending aorta. The seventh dorsal intersegmental artery becomes the left subclavian artery. The aorta becomes interrupted when the left aortic arch IV fails to either develop or connect with the dorsal aortic root segments comprising the descending aorta.
Rarely, do individuals survive to adulthood. Usually survival is a consequence of the ductus and intracardiac communications remaining patent and a marked elevation of the pulmonary vascular resistance to prevent overwhelming flooding of the pulmonary vascular bed. Development of compensatory collateral circulation between the two aortic segments is another possibility.
There are other congenital cardiac anomalies which deserve mention here. These include :
Eisenmenger’s syndrome refers to those patients with a VSD whose shunts have become partially or totally right-to-left as a result of the development of pulmonary vascular disease. This may result from VSD in which, initially, there is significant left-to-right shunting, which causes a compensatory gradual increase in pulmonary vascular resistance, resulting in a right-to-left shunt as the PV resistance approaches or surpasses systemic vascular resistance. Symptoms do not occur until the 2nd or 3rd decade of life, although a more fulminant course may occur. In Eisenmenger’s syndrome, pulmonary vascular resistance is equal to or greater than the systemic vascular resistance, resulting in some right-to-left shunting at rest or with exercise. These patients mostly survive for several decades, lead productive lives, with relatively mild symptoms and few limitations.
Coarctation of the Aorta can occur as a discrete juxtaductal obstruction or as a tubular hypoplasia of the transverse aorta starting at one of the head or neck vessels and extending to the ductal area. Coarctation of the aorta can be associated with Turner’s syndrome. It is postulated that coarctation is initiated in fetal life by the presence of a cardiac abnormality that results in decreased blood flow anterograde through the aortic valve (bicuspid aortic valve or VSD). In the first few days of life, the PDA may serve to widen the juxtaductal area of the aorta and provide temporary relief from the obstruction. If there is concomitant transverse arch hypoplasia, the right ventricular blood is ejected through the ductus to supply the descending aorta, as it does in fetal life. Hypoplastic segments of the aortic isthmus may become completely atretic, resulting in an interrupted aortic arch. Blood pressure is elevated in the vessels that arise proximal to the coarctation. The blood pressure as well as pulse pressure below the constriction are lower. Collateral circulation may develop as a response. Some patients will be asymptomatic, although some children will complain of weakness and/or leg pain with exercise. Older children are also thought to be hypertensive on examination. The classic sign is a disparity in pulsations and blood pressures of the arms and legs. EKG is usually normal in young children, or may reveal some degree of LVH. Most patients succumb between the ages of 20-40, although some may survive well into middle age without serious handicap. The most serious of complications involve premature coronary artery disease, CHF, encephalopathy, and CVA from the hypertensive state. Treatment involves infusion of PGE1 to maintain PDA patency and surgical correction. Patients can have rebound hypertension as a result of the correction and require medical management.
Hypoplastic Left Heart is a term used to describe a closely related group of anomalies that include underdevelopment of the left side of the heart (atresia of the aortic or mitral orifice) and hypoplasia of the ascending aorta. The left ventricle may be small and nonfunctional, or totally atretic. The right ventricle maintains both pulmonary and systemic circulations. Pulmonary venous blood passes through an atrial defect or dilated foramen ovale form the left to the right side of the heart where it mixes with systemic venous blood. When the ventricular septum is intact, as it usually is, the right ventricular blood is ejected intothe main pulmonary artery, while the descending aorta is supplied via the ductus arteriosus, with flow from the ductus also filling the ascending aorta and coronary arteries in a retrograde fashion. Systemic circulation is usually inadequate and cyanosis may develop after the first 48 hours of life. Patients may then go on to develop shock as the PDA starts to close. Peripheral pulses may be weak or absent and there may be a prominent right ventricular parasternal lift. These patients usually do poorly and fail to survive past the first 2-4 weeks of life. A Rashkind balloon atrial septostomy may be done to palliate until a Norwood procedure is done, which is the first of 3 stages of surgery. The only other alternative is a heart transplant.