Ann Thorac Surg 2003;76:572-575
© 2003 The Society of Thoracic Surgeons
Original article: cardiovascular
Implications of anomalous right subclavian artery in the repair of neonatal aortic coarctation
Vibeke E. Hjortdal, MD, PhDa,
Sachin Khambadkone, MD,
Marc R. de Leval, MD,
Victor T. Tsang, MDa*
a Cardiothoracic Unit, Great Ormond Street Hospital for Children National Health Service Trust, London, United Kingdom
Accepted for publication February 21, 2003.
* Address reprint requests to Dr Tsang, Cardiothoracic Unit, Great Ormond Street Hospital for Children NHS Trust, Great Ormond St, London WC1N 3JH, United Kingdom.
e-mail: tsangv{at}gosh.nhs.uk
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Abstract
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BACKGROUND: Spinal cord perfusion is predominantly from the anterior spinal artery, which arises from the vertebral arteries by way of the subclavian arteries. Anomalous origin of the right subclavian artery and coarctation of the aorta is considered to be an increased risk factor for spinal cord damage, possibly because of the minimal collateral circulation during aortic clamping. The aim of this study is to review 5 consecutive cases of neonatal aortic coarctation with ARSA.
METHODS: Five neonates (0.8 to 4.6 kg) underwent operation between July 1999 and December 2000 with resection of the coarctation and end-to-end anastomosis. Both subclavian arteries (n = 5) and left carotid artery (n = 4) were clamped, leaving the right carotid artery as the sole provider of perfusion for the spinal cord.
RESULTS: Despite clamping of both subclavian arteries, right radial artery pressure was measurable in 4 of the 5 cases. Aortic cross-clamp times varied from 12 to 26 minutes at a core temperature of 34° to 35°C. There was no operative mortality. None of the neonates developed any major neurologic sequelae.
CONCLUSIONS: When clamping the two subclavian arteries during coarctation repair, the spinal artery is left with collateral blood flow that can theoretically originate from the carotid arteries through the circle of Willis and retrogradely down the vertebral arteries. The presence of such collateral circulation was documented as recordable blood pressure in the right radial artery during surgical repair.
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Introduction
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Approximately 1% of patients with juxtaductal aortic coarctation have an associated anomalous right subclavian artery (ARSA) arising either proximal [1, 2] or distal [2] to the coarctation site. The most important vascular supply to the spinal cord is through the anterior spinal artery, which arises from the vertebral arteries that subsequently arise from the subclavian arteries.
During coarctation repair in the presence of an ARSA, it is necessary to apply vascular clamps to both subclavian arteries. An increased risk of postoperative complications such as paraplegia has therefore been suspected [3, 4].
It is important to understand the spinal circulation in treating patients with ARSA. The blood supply to the spinal cord is derived from the anterior spinal artery, which in most individuals is a continuous vessel but can occasionally be discontinuous. The blood supply to the anterior spinal artery is divided into superior, middorsal, and dorso-lumbar areas [5]. The superior part (C1 to T2) has a rich blood supply, mainly from branches of the subclavian arteries including the vertebral arteries. The middorsal portion is the least well vascularized and therefore the most vulnerable part, supplied by one or two radicular branches from intercostal arteries. In the dorso-lumbar area, which extends from T8 to the conus terminale, the anterior spinal artery is well supplied by the arteria radicularis anterior magna, also called the artery of Adamkiewicz by whom it was first described.
When clamping the aorta, perfusion of the spinal cord may be disturbed. Hypoperfusion will be most marked in the "watershed" area, which is the third to seventh dorsal segment. Normally this is well tolerated, as collaterals above and below the point of constriction in the aorta will sufficiently supply the anterior spinal artery retrogradely through the thoracic aorta. These collaterals may vary considerably. However, as described in detail by Abbott [2] in 1928, the major collaterals above the constriction arise from the subclavian arteries and their branches such as the internal mammary arteries, vertebral arteries, transverse and descending cervical arteries, and inferior thyroid arteries. Most of the cervical vessels form anastomoses with the first aortic intercostals arising from below the aortic constriction. In addition, the internal mammary arteries form wide anastomoses with the inferior epigastric arteries [2].
During coarctation repair and in the presence of ARSA, it is almost always necessary to clamp both subclavian arteries, thereby eliminating major collateral circulation between the upper and lower body. If the ARSA originates distal to the coarctation, the danger of spinal ischemia may theoretically be even greater because the ARSA may serve as an important antegrade blood supply for the descending thoracic aorta. Within a period of 18 months we have performed operations on 5 neonates with coarctation of aorta and ARSA.
In this article, the anatomy, the hemodynamic findings, and the importance of collaterals in the repair of coarctation of the aorta with ARSA are presented and discussed. Characteristics of the patients whose cases are presented here are given in Table 1.
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Patients and methods
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Patient 1
This infant was twin 2, born at 31 weeks gestation weighing 778 g, and delivered by emergency cesarean section performed for absent end-diastolic placental flow. He was immediately intubated for respiratory failure and later treated for possible necrotizing enterocolitis. At day 14 of life he was transferred to our unit for further investigation of absent femoral pulses. Echocardiography revealed severe coarctation distal to the left subclavian artery, persistent ductus arteriosus, persistent foramen ovale with left to right shunt, bicuspid aortic valve, and left ventricular hypertrophy. A suspicion of ARSA was confirmed. At the age of 25 days he had successful coarctation repair.
Patient 2
This infant was born at term after an uneventful pregnancy and delivery. At the age of 4 days his hemodynamic condition deteriorated and he was transferred, intubated, and ventilated for further investigation. Echocardiography revealed coarctation of the aorta distal to an aberrant right subclavian artery and a restrictive patent ductus arteriosus with left to right shunt. At the age of 11 days, at a weight of 4.6 kg, he underwent a surgical repair and the diagnosis of ARSA was confirmed. In this particular infant, neither of the carotid arteries was clamped at the time of surgery.
Patient 3
This infant was born at 36 weeks. At birth there were no palpable femoral pulses. Echocardiography revealed complex heart disease involving unobstructed total anomalous pulmonary venous drainage of supracardiac type, atrioventricular septal defect with significant left atrioventricular valve regurgitation, coarctation of aorta, and a large secundum atrial septal defect. At the age of 17 days and a weight of 2.5 kg, surgical repair of coarctation of the aorta was performed and an ARSA was found below the coarctation.
Patient 4
This infant was diagnosed prenatally to have Down’s syndrome and atrioventricular septal defect. She was delivered by elective cesarean section at 38 weeks of gestation. Postnatal echocardiography confirmed the prenatal diagnosis and revealed a coarctation of aorta distal to the left subclavian artery and a moderately sized ductus arteriosus. At the age of 7 days and a weight of 3.4 kg, surgical repair of coarctation of aorta was performed and an ARSA coming off below the coarctation was seen. Because of unrecordable right radial artery pressure during surgery, there was concern about spinal perfusion during vascular clamping.
Patient 5
This infant was diagnosed with a juxtaductal coarctation involving the orifice of the left subclavian artery, ARSA, and a hypoplastic distal aortic arch. In addition there was a left superior vena cava to the coronary sinus. At the age of 12 days and a weight of 3 kg, surgical repair was performed with resection of the coarctation and repair with a direct end-to-end anastomosis and reimplantation of the left subclavian artery into the descending thoracic aorta.
The coarctation repair was performed through a left thoracotomy. Body temperature was allowed to drift down to 34°C. The left pleural cavity was flushed with cold saline. The ductus arteriosus was closed. The left common carotid artery, left subclavian artery, aberrant right subclavian artery, and descending thoracic aorta were controlled by side-biting vascular clamps or vessel loops (except in patient 2, in whom it was possible to leave the left carotid artery unclamped). The coarctation was resected and an end-to-end anastomosis was constructed in all 5 cases.
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Results
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During clamping of the aortic arch, leaving the right carotid unclamped (patients 1, 3, 4, and 5) or both carotid arteries unclamped (patient 2), the right arm blood pressure decreased to an unrecordable level in 1 patient (patient 4), to 55% to 75% in 2 patients (patients 2 and 3), remained unchanged in 1 patient (patient 5), and increased in 1 patient (patient 1) (Fig 1).
All 5 neonates were discharged without major neurologic damage.
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Fig 1. Blood pressures (in mm Hg) measured in the right arm before, during, and after coarctation repair. Filled diamonds with solid lines denote patient 1; filled squares with dotted lines, patient 2; filled inverted triangles with dashed lines, patient 3; letter x with dashed lines, patient 4; and letter x (resembling asterisk) with dotted lines, patient 5. (Intraop = intraoperative; preop = preoperative; postop = postoperative.)
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Comment
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Ischemic spinal cord injury is a disastrous complication that may occur after cross-clamping of the thoracic aorta. The reported incidence is approximately 0.5% in children [6, 7]. In infants, the incidence of paraplegia is less well described. Several papers have described coarctation repairs in infants without any spinal cord injury: Lerberg and colleagues [7] (n = 125), Pfammatter and colleagues [8] (n = 46), Han and associates [9]] (n = 42), Conte and associates [10] (n = 95), van Son and coworkers [11] (n = 52), and Allen and associates [12] (n = 53). Four cases of paraplegia secondary to repair of isolated coarctation have been published by Vanhulle and colleagues [13] (n = 1) and by Puntis and Green [14] (n = 3), but these may not be the only cases of spinal cord injury.
Spinal cord injury is normally thought to be due to hypotension during aortic cross-clamping, but it may also be related to intrinsic abnormalities of vascular supply as paralysis or paresis have been reported in coarctation of the aorta without surgery [6] or secondary to operations for other cardiac malformations not involving coarctation of the aorta [14].
Lerberg and colleagues [7] described 1 case of paraplegia among 8 patients who had ARSA and aortic coarctation. The patient had both subclavian arteries clamped during surgery. Interestingly, 6 of the 7 remaining patients also had both subclavian arteries clamped during surgery, and no neurologic problems were detected. Faro and associates [15] also reported 1 case with ARSA and coarctation of the aorta, which was repaired without problems.
Thus the combination of coarctation and ARSA has been reported in 9 patients besides our 5 patients. One of these 14 patients had paraplegia (7%). Because there is only 1 index case, it is impossible to conclude whether the combination of ARSA and coarctation increase the risk of surgically related paraplegia in coarctation repair.
While the subclavian arteries were clamped, blood was redirected through collaterals between the cerebral vessels and the distal part of the right subclavian artery, as documented by the measurable blood pressure in the right arm. In these cases, collaterals originating from sources other than the subclavian arteries must also play an important role in perfusion of the anterior spinal artery. The right arm was probably supplied by the right carotid artery through the circle of Willis retrogradely into the right vertebral artery and subsequently to the right subclavian artery (Fig 2).
It is possible that the anterior spinal artery was perfused through the same intracerebral route and retrogradely through the vertebral arteries. Other routes may also be present, as we found that in 1 case blood pressure in the right arm was unrecordable and there were still no signs of any neurologic damage.
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Fig 2. Anatomy relevant to treatment of anomalous right subclavian artery. The most important blood supply to the spinal cord comes from the spinal artery, which is supplied by the vertebral arteries. A minor supply is from the Adamkiewicz artery. The circle of Willis is a possible communicating circulation between the subclavian arteries and the carotid arteries.
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Occlusion of the transverse arch results in distal hypotension and a resultant decrease in spinal cord perfusion pressure. The lowest possible spinal cord perfusion necessary to avoid ischemic injury is not known. In baboons, paraplegia occurs in all animals when spinal cord flow is reduced from the normal 20 mL per 100 g tissue per minute to 4 mL per 100 g tissue per minute for 60 minutes [16]. There seems to be a direct and significant correlation between the duration of aortic cross-clamping and the frequency of spinal cord injury in adults undergoing operation for acute traumatic aortic transection, with a cutoff at 25 minutes [17]. In children and infants this correlation has not been established. Most surgeons would consider an aortic clamping time of less than 25 to 30 minutes as "safe," although this has never been proved. Brewer and coworkers [6] analyzed 12,532 cases of repair of coarctation of aorta with 51 cases (4 per 1,000) of paraplegia. He reported cross-clamping for 1 to 4 hours without paralysis and concluded that the time of occlusion was not related to spinal cord injuries. Lerberg and colleagues [7], on the contrary, reported an incidence of paraplegia of 1.5% and found that 4 children with paraplegia had a longer cross-clamp time (average 49 minutes, range 40 to 72 minutes) compared with the average cross-clamp time in the group as a whole.
Because neurologic damage is time dependent in adults, short clamp times are probably also advisable in infants, although this advice is based on retrospective studies [7] and is common sense more than strict scientific knowledge. Cross-clamp times of less than 25 minutes are generally considered safe, as no one has reported spinal cord injury with such short clamp times. From a theoretical point of view, decreased metabolic turnover would allow a correspondingly longer clamp time. Cooling is, so far, the only applicable way of decreasing metabolic turnover. Preservation of spinal cord flow during operations for coarctation using cardiopulmonary bypass techniques may theoretically be advantageous but it may not be a foolproof method. Svensson and colleagues [18] showed that distal aortic perfusion protects the spinal cord below the arteria radicularis magna but not above it because of the unique vascular anatomy of the anterior spinal artery, which is smaller above than below the entry of the arteria radicularis magna. The resistance to flow is therefore many times greater in the segment above the entry of the Adamkiewicz artery.
Because paraplegia can occur in any patient and may be beyond the control of the surgeon, the only advice that can be given without reservation is to have current information made available to the patient or parents before the operation.
Clamping both subclavian arteries during coarctation repair for up to 26 minutes appears to be safe in neonates. The presence of a collateral circulation was documented as recordable blood pressure in the right radial artery. However, this does not necessarily indicate safety in older children.
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Acknowledgments
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Research at the Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust benefits from Research and Development funding received from the NHS Executive. We thank Faith Hanstater for her assistance with the preparation of this manuscript.
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References
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Abstract
Introduction
