Case report

A five-week-old baby girl was admitted to British Columbia Children's Hospital with failure to thrive and cyanosis. The pregnancy, which was the result of in-vitro fertilization, had been uneventful and was the mother's first. Delivery was by cesarean section for breech position at term. The family history was unremarkable for congenital cardiac disease. Examination revealed a bright, alert, baby with a heart rate of 150 beats/min, oxygen saturations between 75 and 90%, and an increased respiratory rate when settled. There was a loud second pulmonary sound, a systolic murmur, hepatomegaly, good pulses in the feet, and normal capillary refill. Echocardiography showed severe mitral stenosis, a small left ventricle, a bifoliate aortic valve, a large ventricular septal defect with right-to-left shunting, an intact atrial septum, mild tricuspid regurgitation, systemic to supra-systemic pulmonary arterial pressures, an unusual aortic arch, and a persistent left superior caval vein draining to the coronary sinus (Fig. 1).

Figure 1. Echocardiographic parasternal four chamber view of the heart. The left ventricle is not apex-forming, the mitral valve is dysplastic, and there is a ventricular septal defect. LA: left atrium; LV: left ventricle; MV: mitral valve; RA: right atrium; RV: right ventricle.

Computed tomographic angiography (Phillips Mx 8000, Phillips Medical Systems Canada, Markham, ON) showed a right aortic arch giving rise to right common carotid, vertebral and subclavian arteries, mild hypoplasia of the retroesophageal transverse arch, a leftward aberrant brachiocephalic artery with a remnant of the arterial duct, and a leftward descending aorta. The right superior and inferior caval veins drained to the right atrium, as did a persistent left superior caval vein via the coronary sinus.

We planned a modification of the Norwood procedure, consisting of anastomosis of the divided pulmonary trunk to the aorta, augmentation of as much of the arch as possible, atrial septectomy and construction of a systemic-to-pulmonary arterial shunt. At surgery, the aorta and right atrium were cannulated for cardiopulmonary bypass, and the baby was cooled to a rectal temperature of 16°C, during which the left-sided and posterior arterial duct was divided. A 4-mm polytetrafluoroethelene graft was anastomosed to the base of the left common carotid artery. Under a period of circulatory arrest, the proximal pulmonary trunk was anastomosed to the ascending aorta, and the incision extended distally underneath the right common carotid artery as far as was possible into the arch. The anastomosis was completed with a gusset of pulmonary arterial homograft. Following atrial septectomy, cardiopulmonary bypass was then reinstituted, and the distal end of the shunt was anastomosed to the anterior wall of the bifurcation of the pulmonary trunk after patching it with a pulmonary arterial homograft. Revision of the distal end of the shunt was required before separation from cardiopulmonary bypass. Nitric oxide was administered for pulmonary hypertension. Dopamine, epinephrine, milrinone, and phenoxybenzamine were all administered. The sternum was left open, and the baby was transferred to the intensive care unit. The sternum was closed on the second postoperative day, and the baby was discharged from hospital on the eighteenth postoperative day.

The child has since undergone bilateral bidirectional cavopulmonary shunting, with division of the left modified Blalock–Taussig shunt, and is awaiting completion of the Fontan circulation. Breath-held computed tomographic angiography, with the patient anesthetized, was performed following the bidirectional cavopulmonary shunting, and confirmed the abnormal anatomy of the aortic arch (Fig. 2).

Figure 2. Surface rendered re-constructed images from an axially-acquired three dimensional data set from a computerized tomographic angiogram, viewed in (a) left anterior oblique and (b) cranially-tilted frontal projections. The reconstructed ascending aorta (red) following the Damus–Kaye–Stansel procedure ascends on the right of the trachea (blue) and gives off 3 vessels in the sequence: the right common carotid, right vertebral and right subclavian arteries. The transverse arch crosses to the left side of the mediastinum posterior to the trachea and esophagus (yellow). The brachiocephalic artery arises to the left of the midline, and supplies the left common carotid and left subclavian arteries. Following ductal division and placement of a modified left Blalock–Taussig shunt, and its subsequent division, the proximal end of the shunt (*) is seen arising from the base of the left common carotid artery. DA: descending aorta; LCCA: left common carotid artery; LBA: left brachiocephalic artery; LSA: left subclavian artery; RCCA: right common carotid artery; RSA: right subclavian artery; RVA: right vertebral artery.

Discussion

A right aortic arch with an aberrant retroesophageal left brachiocephalic artery is a well-recognized malformation of the aortic arch, but is exceedingly rare.¹ The right arch gives origin to the right common carotid and subclavian arteries. The transverse arch then usually crosses to the left of the mediastinum posterior to the trachea and esophagus, giving off a left-sided brachiocephalic artery before descending on the left. A left arterial duct, connecting the base of the aberrant brachiocephalic artery to the left pulmonary artery, completes a vascular ring. Embryologically, this arch variant occurs as a result of interruption of the left arch of the hypothetical double arch of Edwards between the ascending aorta and the left common carotid artery, with the brachiocephalic artery filling from the dorsal left aortic root.³ If the aorta were to descend on the right, the aberrant brachiocephalic artery itself would form the retroesophageal component of the potential vascular ring. If the descending aorta is left-sided, the retroesophageal component is formed by the transverse arch. In either case, the potential vascular ring is completed by the left arterial duct connecting to the left pulmonary artery.

Traditionally, vascular rings have been investigated using the chest X-ray, barium swallow, cardiac catheterization, and angiography. The first two modalities remain useful for demonstrating compromise of the airway and oesophagus. Cross-sectional imaging, with a computed tomographic scan or magnetic resonance imaging, is now replacing cardiac catheterization because these techniques are less invasive, and have the potential for multiplanar reconstruction of data, with the three dimensional display facilitating both diagnosis and surgical planning.

Our case adds to the literature by describing these findings in association with repair of hypoplastic left heart syndrome in early infancy. A shunt was done from the base of the most accessible vessel arising from the aberrant left brachiocephalic artery, as this was the most direct route to the bifurcation of the pulmonary trunk. Although this reconstituted the vascular ring after division of the ductal remnant, the shunt was subsequently divided at the time of construction of the bidirectional cavopulmonary shunt. Placing the proximal end of the shunt at the base of the right common carotid artery would have caused it to curve over the anterior aspect of the Damus–Kay–Stansel connection. Alternatively, a conduit could be placed from the right ventricle to the pulmonary trunk.⁴ A shunt of 4 mm diameter was used, and nitric oxide was needed since pulmonary hypertension was present.⁵ If there is obstruction caused by the hypoplastic retroesophageal transverse arch, then a graft can be placed from the ascending to the descending aorta.^{6, 7}