Isolated left subclavian artery occurs when the left subclavian artery is not connected to the arch or the left common carotid artery, but rather it is attached to the left pulmonary artery via a left sided ductus arteriosus; therefore, filling of the isolated subclavian artery is from the vertebral artery in a retrograde fashion(6). Isolated left subclavian artery is a rare aortic arch anomaly which is associated with the right aortic arch. However, only 0.8% of right aortic arch cases have isolated subclavian artery (7). As we expected, our patient also had a right sided aortic arch.
In most cases, the isolated left subclavian artery is asymptomatic and does not cause a vascular ring. Symptoms, if present, including discrepancy between the two upper limbs in terms of size, pulse or blood pressure (8). However, in our patient due to systemic pulmonary hypertension, neither blood pressure nor pulses was lower in the upper left limb and the size of both upper limbs was similar.
In isolated subclavian artery, subclavian steal syndrome and pulmonary steal syndrome are also expected. In subclavian steal syndrome, the blood flow required by the subclavian artery is supplied via retrograde flow from the vertebro-basilar circulation, which in turn causes symptoms of vertebro-basilar insufficiency, especially during exercise. Our patients did not have any sign or symptoms of vertebro-basilar insufficiency, and the brain was found to be normal on the patient’s brain CT scan.
Pulmonary Steal Syndrome occurs when pulmonary vascular resistance decreased in early infancy. Therefore, retrograde blood flow from the vertebral artery to the subclavian artery, and then to the pulmonary artery. This situation results in ischemia of the brain on one side and pulmonary congestion on the other. (9) Although since our patient had systemic pulmonary hypertension, the Pulmonary Steal phenomenon was not expected.
In up to 60% of isolated left subclavian cases, there are co-existent congenital heart defects, mostly Conotruncul anomalies such as double outlet right ventricle and tetralogy of Fallot, atrial septal defects and ventricular septal defects (9). Not surprisingly, our patient has multiple ventricular septal defects, the largest of which was a Perimambranous VSD with 6 mm diameter. On the other hand, extra-cardiac anomalies and genetic syndromes such as 22q11 deletion are more common in patients with aortic arch anomalies, especially in right aortic arch cases(8) Our patient did not have a thymus, so even though without a syndromic appearance, she was considered Digeorge syndrome and consequently genetic study requested for her.
Since our patient had multiple ventricular septal defects (Swiss cheese ventricular septum), based on the current guidelines, pulmonary artery banding was the preferred surgery for her. Reviewing the literature demonstrated that surgical reimplantation of the isolated left subclavian along with ductus arteriosus ligation have had acceptable outcomes, however, we did not perform it for our patient. As a replacement, we did ligation of the isolated left subclavian origin from the pulmonary artery. Obviously, in the follow-up period, evaluation of the size of the upper limbs as well as development of sign or symptoms of vertebra-basilar insufficiency seems necessary.