The term coarctation derives from the Latin coarctare, to compress. Coarctation of the aorta (CoA) is defined as a congenital narrowing of the aorta that is hemodynamically significant. CoA occurs in more than 4 in 10,000 live births and accounts for more than 5 percent of anomalies in children born with congenital heart defects.¹ Although isolated coarctation is more common in males, coarctation associated with other cardiac lesions occurs with equal frequency in males and females.

CoA can occur along the entire length of the aorta, but is most commonly located proximal to the junction of the ductus arteriosus and the descending aorta (Fig. 79-1). A posterior protuberance of the media, often augmented by ductal tissue, typically creates a “shelf” that protrudes into the aortic lumen. Externally, the aorta may be visibly narrowed, but often to a lesser extent than observed within the lumen. In addition, the aortic isthmus, defined as the segment between the left subclavian artery and the ductus arteriosus, is frequently hypoplastic. In some patients, hypoplasia may involve the entire transverse aortic arch. There are numerous classification systems, all of which are essentially descriptive.

The first description of aortic coarctation is credited to Paris in 1791, whereas the first published report of repair by resection and end-to-end anastomosis was by Crafoord in 1944.^2,3 Gross independently described a nearly identical repair in 1945 and was the first to describe the technique of interposition grafting.^4,5 Effective augmentation of the narrowed aortic segment with patch aortoplasty was described by Vossschulte in 1957, while Waldhausen introduced the subclavian flap aortoplasty in 1966.^6,7

Etiology

The etiology of aortic coarctation is unknown. Coarctation may be associated with genetic anomalies including Turner syndrome (45X,O) and Noonan syndrome; to date, however, no specific or reproducible molecular abnormality has been identified. In the fetal circulation, right-to-left flow through the ductus arteriosus results in decreased flow across the aortic isthmus with respect to either the ascending or descending aorta. Following postnatal ductal closure, the normal aorta presumably expands and grows in response to increased flow and pressure. This concept is corroborated by an increased incidence of CoA in patients with lesions associated with diminished aortic flow, such as aortic stenosis, ventricular septal defect (VSD), and mitral valve pathology. Furthermore, coarctation is rarely seen in lesions that result in increased aortic flow, such as tetralogy of Fallot.

It has been well recognized that the presence of ductal tissue within the aorta may contribute to this process. The muscular wall of the ductus arteriosus is exquisitely sensitive to changes in neonatal hemodynamics and to pharmacologic agents such as prostaglandin (PGE1) and nonsteroidal anti-inflammatory agents. In some patients, ductal tissue extends well into the adjacent aortic wall and, during ductal contraction, may contribute to the development of coarctation. These findings have been confirmed in histologic studies.⁸ Additional biochemical factors have been identified in patients with CoA. The aortic isthmus and, in some, the transverse arch exhibit a higher fraction of elastin lamellae and a lower fraction of α-actin-positive cells. These findings may account for decreased aortic growth.⁹

Clinical Features

Clinical presentation is determined by the location and degree of aortic narrowing as well as the presence of associated intra- or extracardiac anomalies. Although neonates may appear normal at birth, they develop evidence of aortic obstruction with ductal closure. Manifestations include poor feeding, irritability, and tachypnea. A persistent systolic precordial murmur in the setting of weak or absent femoral pulses should raise the suspicion of aortic coarctation. Other presenting signs include differential oxygen saturations between upper and lower extremities and pulmonary overcirculation from left to right shunting across the patent foramen ovale. In the most severe form, with ductal closure over the first days to weeks of life, the sudden increase in afterload on the nonhypertrophied left ventricle results in a marked decrease in left-sided stroke volume and ejection fraction. Cardiomegaly results from an acute increase in right ventricular end-diastolic volume consequent to increased left-to-right shunting through the patent foramen ovale.¹⁰ Poor perfusion and listlessness may occur. Femoral pulses are not palpable and metabolic acidosis ensues. If CoA is left untreated, end-organ damage (including renal failure and necrotizing enterocolitis) will ultimately result in death.

Infants who undergo more gradual closure of the ductus may develop arterial collaterals, allowing for a less catastrophic presentation. In such cases, the most common finding is usually failure to thrive. These children often have difficulty with feedings and diaphoresis. Physiologically, these infants have compensated for the increase in afterload and present with left ventricular hypertrophy. Older children and adults not diagnosed in infancy (presumably due to less severe disease) commonly present with unexplained hypertension or during the workup of a murmur. Lower extremity pulses are delayed or absent, exercise tolerance may be diminished, and claudication may be a chief complaint. Other symptoms include manifestations of upper body hypertension such as headache, epistaxis, visual field disturbances, and stroke.

Associated Anomalies

In one report, 82 percent of all coarctations were isolated, 11 percent were associated with a VSD, and complex anatomy was observed in 7 percent.¹¹ CoA is associated with a bicuspid aortic valve in approximately 50 percent of patients.¹² Since CoA creates a pressure load on the left heart, a patent foramen ovale with a left-to-right shunt is often present. Aortic coarctation occurs in less than 10 percent of patients with transposition of the great vessels and in up to 50 percent of patients with the Taussig–Bing Anomaly (see Chapter 71).^13,14 In these patients, conal malalignment may produce subaortic obstruction with decreased antegrade flow through the transverse arch and isthmus. Hypoplastic left heart syndrome has an 80 percent incidence of CoA.¹⁵ Coarctation is also associated with other forms of functional single ventricle, including tricuspid atresia with transposition of the great arteries and double-inlet left ventricle. Shone complex is characterized by a parachute mitral valve, supra-annular mitral ring, subaortic stenosis, and CoA. These patients present with a spectrum of disease, the most severe of which requires single ventricle palliation.

Natural History

Unrecognized CoA is rare in the current era. Untreated coarctation leads to premature death due to complications of unrelenting hypertension, with its attendant effects on the coronary and cerebral circulation. These effects include coronary artery disease, cerebrovascular accidents (both aneurysmal and atherosclerotic), congestive heart failure, and aortic rupture. In addition (particularly in patients with bicuspid aortic valves) bacterial endocarditis can occur. The survival of untreated patients with isolated CoA is depicted in Figure 79-2.

Diagnostic Modalities

The principal method of diagnosis early in life is echocardiography. In the neonate and infant, the presence of a large thymus allows for excellent visualization of the arch structures (Fig. 79-3). Surface echocardiography provides specific anatomic information including location, length (diffuse versus discrete narrowing), and dimension of the coarctation segment. Severity of obstruction can be assessed quantitatively by measurement of Doppler flow velocity and qualitatively by evaluation of abdominal aortic pulsatility and diastolic flow. The presence of left ventricular hypertrophy also suggests increased severity. In addition, echocardiography allows for the detection of associated intracardiac lesions and transverse arch hypoplasia. In the presence of a patent ductus arteriosus, the ability of echocardiography to diagnose CoA may be limited. As thymic regression ensues, the interposition of lung tissue between the arch and the chest wall obscures echocardiographic details, making echocardiography less useful in older children and adults. In this particular age group, the use of cross-sectional imaging, such as thin-slice computed tomography and magnetic resonance imaging, provides excellent structural detail of the aortic arch and its branches. In addition, as these modalities provide imaging of the entire chest and abdomen, the detection of important collateral arteries is feasible.

Angiography (traditionally viewed as the “gold standard” for aortic evaluation) is now rarely used for diagnosis, as it is invasive and exposes the patient to a nephrotoxic contrast load (Fig. 79-4). However, angiography may be considered with the objective of delineating unclear anatomy and when percutaneous intervention is contemplated.

Medical Therapy

The role of medical therapy in the treatment of hemodynamically significant CoA is limited to temporizing measures while the timing and method of surgical repair are being considered. The mainstay of medical therapy in neonates is intravenous PGE1 infusion. This maintains patency of the ductus arteriosus, allowing for resuscitation and restoration of end-organ perfusion in compromised infants. Side-effects of PGE1 include generalized edema, hypotension and apnea, sometimes requiring preoperative mechanical ventilation.

In patients who have undergone repair and in those in whom the diagnosis is made later in life, the surveillance and treatment of hypertension is paramount.

Catheter-Based Intervention

Successful primary treatment of aortic coarctation by balloon angioplasty has been reported but requires further investigation to define its overall efficacy, safety, and long-term durability. The main limitations of balloon angioplasty, particularly in the neonate, are early recurrence of coarctation, aneurysm formation, and access-related injury to the femoral artery. In a recent retrospective review, nearly 60 percent of neonates undergoing primary balloon angioplasty required subsequent surgical repair, and 13 percent developed saccular aneurysms. In the surgical repair group, 18 percent developed recoarctation responsive to balloon dilatation, and no patients developed aneurysms.¹⁶ Balloon angioplasty has a limited role in critically ill neonates who are poor surgical candidates because of severe left ventricular dysfunction or intercurrent illness, allowing for palliation until surgical correction can be safely undertaken. Balloon angioplasty is nevertheless the treatment of choice for recurrent coarctation following neonatal surgical repair, with a greater than 90 percent success rate at relieving the gradient and a 16 percent incidence of restenosis requiring reintervention.¹⁷

Endovascular stents provide durable relief of aortic coarctation in older children and adults. Stents have a significant advantage over simple angioplasty in that they prevent elastic recoil of the aortic wall, reducing the likelihood of dissection during the procedure. Stent placement in younger children, however, is generally not preferable. Smaller stents cannot undergo serial dilation to keep pace with somatic growth, resulting in the eventual need for a technically difficult surgical repair. Larger stents may allow serial dilatation, but the size of the femoral artery often precludes stent placement in smaller patients. As with surgical intervention, persistent hypertension despite successful relief of obstruction requires diligent surveillance and treatment. In a review of endovascular treatment of CoA in adolescents and adults (1-year follow-up), all patients had persistent resolution of their aortic gradient, with a 13 percent incidence of small aneurysms.¹⁸ Although long-term data are not yet available, midterm results appear to compare favorably with surgical repair.

Surgical Therapy

Surgical correction is indicated for all symptomatic neonates and infants, as well as older children and adults who are not candidates for transcatheter therapy. Operation should be considered in asymptomatic patients for an upper-to-lower extremity mean blood pressure gradient in excess of 20 mm Hg that is associated with upper extremity hypertension and a greater than 50 percent reduction in luminal diameter in the coarctation segment. A low gradient in the presence of robust collateral development does not exclude severe obstruction and should not be considered a contraindication to surgery.

Following induction of general anesthesia, a right radial arterial line is inserted and the patient is placed in the right lateral decubitus position (for left-sided descending aorta). A left posterolateral thoracotomy through the fourth intercostal space provides ideal exposure for most repairs. Alternatively, a muscle-sparing extrapleural approach can provide adequate exposure with comparable results.¹⁹ In cases requiring associated intracardiac repair or complex transverse arch reconstruction, median sternotomy and cardiopulmonary bypass with circulatory arrest may be utilized; a description of these more complex techniques is beyond the scope of this discussion. Following thoracotomy, the lung is retracted anteroinferiorly and the pleura overlying the aorta and left subclavian artery is incised longitudinally. If present, a supreme intercostal vein and any crossing lymphatics are ligated and divided to prevent the occurrence of a chylothorax. Care is taken to preserve the left vagus nerve and the recurrent laryngeal nerve as it passes around the ligamentum arteriosum or PDA. The pleural edges are suspended by sutures to aid in exposure and retraction of the lung (Fig. 79-5). For all methods of reconstruction, dissection and control of the proximal aortic arch, left common carotid and subclavian arteries, descending aorta, ductus arteriosus, and intercostal arteries is essential for safe repair. Although it is preferable to preserve the intercostal arteries when possible, several pairs may be sacrificed to obtain a tension-free anastomosis.

Resection with end-to-end Anastomosis

The ductus arteriosus is ligated and divided. The proximal aorta is clamped obliquely across the left subclavian artery and transverse aortic arch. The distal aorta is clamped well below the planned resection and anastomotic site. In young patients, the left common carotid artery may be safely occluded by the proximal clamp, but the innominate artery must remain patent to preserve cardiac output and cerebral blood flow. This is confirmed by an adequate waveform on the right radial artery pressure monitor and maintained cerebral infrared spectroscopy data (NIRS). In older patients, occlusion of the left common carotid artery may be inadvisable. Care is taken to ensure that the clamps do not distort the area of reconstruction or compress the innominate artery. Intercostal arteries that backbleed into the field should be controlled by temporary clips or snares. The coarctation segment is completely resected, including all ductal tissue macroscopically visible within the aorta. The aorta is then reapproximated in a running fashion using 7-0 suture in neonates and small infants (Fig. 79-6). Interrupted suture placement or the use of absorbable suture material has not been shown to improve results. Generally, a clamp time of less than 30 minutes is felt to be safe. Mild hypothermia is employed by many groups to reduce the risk of spinal cord ischemia.

The primary advantage of resection and end-to-end anastomosis is the complete excision of all abnormal aortic tissue. However, adequate mobilization is required to create a tension-free anastomosis. Mobilization of the distal aorta risks injury to fragile intercostal and collateral vessels in older children and adults. Other techniques of repair may therefore be more appropriate in this age group.

Extended resection with end-to-end anastomosis is necessary in the presence of severe transverse arch hypoplasia. The proximal clamp is placed to the level of the innominate artery and ascending aorta. After the coarctation segment is resected, the underside of the aortic arch is spatulated and anastomosed to the appropriately beveled descending aorta (Fig. 79-7). This results in a larger effective anastomotic orifice area. Extensive proximal and distal mobilization is necessary to allow tension-free approximation.

Subclavian Flap Aortoplasty

Full mobilization of the left subclavian artery is required for this repair. The left subclavian artery is ligated at the level of its first branch, taking care to preserve all distal branches, as they provide the collateral circulation to the left arm. Some surgeons additionally ligate the vertebral artery to prevent late subclavian steal syndrome. The ductus is ligated and a longitudinal aortotomy is begun distal to the area of coarctation. The incision is extended proximally across the coarctation site and into the left subclavian artery, ending just proximal to the previously placed ligature. The left subclavian artery is only then transected and the resulting subclavian flap is turned inferiorly and sutured to the edges of the descending aorta (Fig. 79-8). A “reverse” subclavian flap may be used less commonly for discrete coarctation proximal to the left subclavian artery or distal transverse arch hypoplasia (Fig. 79-9). A reverse subclavian flap aortoplasty can also be combined with an end-to-end anastomosis to address distal arch and isthmic hypoplasia in the setting of coarctation.

The advantages of subclavian flap aortoplasty include ease of repair and the avoidance of extensive aortic mobilization. Adequate length and caliber of the subclavian artery should be ascertained when considering this technique. Subclavian flap aortoplasty is generally avoided beyond infancy because of concern with upper extremity perfusion.

Patch Aortoplasty

Following clamp placement, the aorta is incised longitudinally across the coarctation, from the left subclavian artery origin to the level of the first intercostal artery (Fig. 79-10). The coarctation ridge is typically not excised, and an oval patch of prosthetic material is fashioned and sutured to the aortotomy margin using continuous suture technique. Care is taken to ensure that the widest portion of the patch overlies the coarctation ridge.