Perioperative and Anesthetic Management of Coarctation of the Aorta

Introduction

Coarctation of the aorta refers to a discrete narrowing of the aortic lumen, typically located adjacent to the insertion of the ductus arteriosus, that causes varying degrees of left ventricular (LV) pressure overload and decreased lower body perfusion. The first mention of coarctation was made in 1760 by Giovanni Morgagni, followed by a more complete description of the lesion and accompanying pathology by French anatomist M. Paris in 1789 and 1791. ¹

Coarctation of the aorta occurs in approximately 1.7 to 4 per 10 000 live births and represents 7.5% of congenital heart disease.^2-4 Various historical reports have demonstrated a male preponderance, but this finding may have been attributable to detection bias.^4,5 Coarctation often occurs with other congenital heart anomalies. In severely symptomatic neonates, one study demonstrated 40% to have isolated coarctation, whereas 36% also had a ventricular septal defect (VSD), and the remainder had more complex anomalies such as transposition of the great arteries, hypoplastic ventricle, truncus arteriosus, and double outlet right ventricle. ⁶ Coarctation is often seen in the setting of Shone’s complex, coexisting with left sided obstructive lesions such as mitral ring, parachute mitral valve, subaortic membrane, and aortic stenosis. In a case series of primarily adult patients, isolated coarctation was seen in 16.2% of patients. Bicuspid aortic valve was the most common associated abnormality (60%), followed by distal arch hypoplasia (14.2%), VSD (12.8%), patent ductus arteriosus (PDA; 7%), and other less common anomalies. Most cases of coarctation are thought to be sporadic; however, a genetic component is suggested by familial cases and the known association with Turner syndrome.^7,8

Anatomy, Embryology, and Classification

For the purposes of nomenclature, the aorta is divided into the aortic root, the ascending aorta, the aortic arch, the isthmus, and the descending aorta. The root includes the aortic annulus, the sinus of Valsalva, and the sino-tubular junction (STJ). The ascending aorta extends from the STJ to the innominate artery. The proximal arch includes the innominate artery to the left carotid artery, and the distal arch extends from the left carotid to the left subclavian artery. The isthmus joins the arch to the descending aorta. The normal aortic size decreases from the ascending aorta to the descending aorta, with the latter being about 40% the size of the former.^9,10 Aortic sizes in pediatric patients are usually reported with a standard deviation or z-score compared to normal values and indexed to body size. A z-score of less than −2 is usually considered a critical narrowing that would warrant repair. ¹¹

Coarctation of the aorta can be either congenital or acquired. Acquired coarctation usually occurs in the arch or the descending aorta and is typically secondary to inflammatory arteritis or aortic atheromatosis.^12,13 More commonly, coarctation of the aorta is congenital. Although the pathophysiology has not been fully elucidated, altered flow patterns across the PDA and aortic arch in utero likely play a role. Coarctation of the aorta is more common than usual when there is decreased flow out of the ascending aorta during fetal development, as occurs with a posterior malaligned VSD, aortic stenosis, mitral stenosis, and mitral regurgitation. Coarctation is uncommon in lesions where there is increased flow across the isthmus, as occurs in right-sided obstructive lesions.^14,15 Extension of ductal tissue into the descending aorta has also been implicated in coarctation, where it can form a shelf around the periductal aorta^16,17 (Figure 1). The ductal tissue can proliferate after birth and cause restenosis after repair. ¹⁷ Indeed, there have been cases where prostaglandin E₁ (PGE₁) has improved the hemodynamics in neonates by relaxing the ductal tissue at the site of coarctation without reopening the ductus. ¹⁸

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Figure 1.

Prenatal and postnatal blood flow with normal anatomy and with aortic coarctation. The images demonstrate normal regression of the patent ductus arteriosus (PDA; A) and abnormal development of a “shelf” with PDA closure contributing to the formation of a coarctation (B). Reprinted with permission under International Association of Scientific, Technical, and Medical Publishers Association (STM) signatory guidelines from Hutchins. ¹⁵

In coarctation, the aortic walls are continuous above and below the lesion, which distinguishes the lesion from interrupted aortic arch. Whereas previously classified as infantile (preductal) or adult (postductal), essentially all congenital aortic coarctation is periductal, and the age of presentation is more dependent on the severity of the lesion and associated cardiac defects.^14,19 The left subclavian artery may be proximal, distal, or at the level of the coarctation. In 70% of cases, the coarctation is discrete, involving only the area of the isthmus; in 30% of cases, the distal arch is involved. The proximal arch is rarely small enough to require intervention in patients with isolated coarctation. ⁹ In general, however, the normal taper in the size of the aorta is more pronounced in patients with coarctation.^9,20 In the setting of an anomalous origin of the right subclavian artery, the right subclavian may originate distal to the coarctation. ²¹

Physiology and Diagnosis

Coarctation of the aorta is an obstructive lesion that leads to varying degrees of LV pressure overload and LV hypertrophy commensurate with the severity of the lesion. In utero, however, coarctation of the aorta has little physiological consequence for the fetus because the majority of blood flow to the abdomen and lower extremities comes from the ductus arteriosus and bypasses the narrowed aortic segment (Figure 1). After birth, as pulmonary vascular resistance drops and the ductus arteriosus begins to close, patients with severe lesions will manifest with progressive heart failure and shock. ²² These infants can develop severe end-organ dysfunction and death without prompt initiation of PGE₁ to reopen the ductus arteriosus. In less severe lesions, diagnosis is more often delayed, and collateral circulation develops to attenuate the hemodynamic consequences of the coarctation. Collateral circulation is poorly developed in newborns with coarctation but usually becomes increasingly robust as the patient ages.^23,24 Collateral flow originates from the subclavian arteries and supplies the descending aorta primarily via the intercostal, inferior epigastric, and subscapular arteries (Figure 2).

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Figure 2.

Major collaterals in aortic coarctation and the vessels that supply them. Reprinted with permission under STM Association signatory guidelines from Edwards and Clagett. ²³

Presenting signs and symptoms depend on the age of the child, the severity of the coarctation, and the presence of associated cardiac lesions. Infants with severe isolated coarctation may present with signs of heart failure such as feeding problems, sweating, and tachypnea. Differential cyanosis, meaning a higher oxygen saturation in the right arm compared to the lower extremities, can also be seen with right-to-left shunting across a PDA. ²⁴ Coarctation in older children may be discovered because of asymptomatic hypertension diagnosed during a routine exam. Classic physical findings include absent, weak, or delayed femoral pulses, and children with normal arch anatomy will have a blood pressure gradient between the right arm and lower extremities. Some may have symptoms such as headache, fatigue, dyspnea, and lower extremity claudication. ²⁵

Diagnosis of coarctation can be suggested prenatally by fetal ultrasound, though definitive diagnosis is difficult and usually requires confirmation postnatally by transthoracic echocardiogram (TTE).^24,26 During the initial TTE, 2-dimensional (2D) and Doppler techniques are required to characterize the lesion. On 2D echocardiography, the dimensions of the aorta are measured, and the branching pattern of the arch is determined. A prominent shelf may be visible in the area of the coarctation. Color flow Doppler and continuous wave Doppler are used to identify and quantify the velocity across the coarctation and, thus, the degree of stenosis. Coarctation can be difficult to diagnose in the setting of a PDA because ductal flow interferes with velocity measurements. In the absence of a PDA, an increase in flow velocity across the aorta is consistent with coarctation. ²⁴ Given the high incidence of associated lesions, a comprehensive TTE should be performed, including a thorough evaluation of the entire aortic arch to assess coexisting arch hypoplasia. ²⁵ Computed tomography (CT), CT angiography, and magnetic resonance imaging (MRI) can lend useful anatomical information and are more sensitive than echocardiography for detecting coarctation.^24,27 MRI can provide high-quality images and volumetric data (eg, measures of collateral flow) and can assist with severity classification in the setting of significant collateral flow because collateral flow implies less flow through the obstructed aortic segment. ²⁸ Cardiac catheterization can be used both to aid diagnosis as well as for therapeutic interventions such as angioplasty and stenting. It should be realized that gradients across the coarctation can be artificially decreased in the setting of significant collaterals or decreased myocardial function. Aortography can be used to visualize the degree of stenosis, and hemodynamic catheterization can provide measures of cardiac function that may affect diagnosis. ²⁴ Pressure criteria for diagnosis include a transcoarctation gradient >20 mm Hg or a gradient <20 mm Hg with collaterals or reduced cardiac output. Given the myriad imaging techniques, it is rarely necessary for catheterization to be used if an intervention is not planned.

Natural History

Surgical correction of aortic coarctation was first performed in 1944 and reported in 1945.^1,29 Prior to the availability of surgical correction, several large autopsy series demonstrated a mean age at death of 34 years for individuals with aortic coarctation, with congestive heart failure, aortic rupture, bacterial endocarditis, and intracranial hemorrhage being the most commonly cited proximal causes of death. ³⁰ Overall, 90% of untreated individuals die by the age of 50 years. ³⁰ Surgical correction rapidly became the standard of care, given the significant early morbidity and mortality associated with untreated or medically managed aortic coarctation. ⁴

Surgical and Catheter-Based Repair

Early intervention is thought to decrease the risk of developing late hypertension and its associated sequelae.^25,31 Either surgical repair or percutaneous catheter-based interventions are used in the treatment of aortic coarctation. The choice of procedure for an isolated coarctation depends on the age of the patient, the ventricular function, the extent of the narrowing, and institutional preferences (see Figure 3).

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Figure 3.

Algorithm for repair of coarctation of the aorta at Seattle Children’s Hospital. It should be noted that surgery refers to coarctation repair (and not transplant).

Surgical Repair

Options for surgical repair include resection of the narrowed segment with end-to-end or end-to-side anastomosis, subclavian flap aortoplasty, resection and graft interposition, or prosthetic patch aortoplasty (Figures 4 and 5). Extended end-to-end repair, radically extended end-to end repair, or reverse subclavian flap aortoplasty can be used when the coarctation extends to the distal arch (Figures 4 and 6).^9,32 The chosen surgical technique will be largely dictated by the patient’s individual anatomy; however, patch aortoplasty is usually avoided if possible given a much higher rate of aneurysm formation than other techniques. ³³ The surgical approach is generally through a left posterolateral thoracotomy with the patient in the right lateral decubitus position. Dissection and exposure can be difficult in older children and adults because of the presence of collaterals. ²⁴ The aorta is mobilized as much as possible to have a tension-free anastomosis. After exposure cross-clamps are placed on the proximal and distal aorta during the repair. In teenagers and adults, some centers will use left-heart bypass or, rarely, full cardiopulmonary bypass (CPB) with femoral cannulation, as discussed below. When there is diffuse arch hypoplasia, a sternotomy with CPB and regional cerebral perfusion or deep hypothermic circulatory arrest is required.

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Figure 4.

A. End-to-end and extended end-to-end surgical repair. In an end-to-end anastomosis, the aorta is mobilized, the coarctation is isolated with proximal and distal clamps, and the area is resected and reanastomosed. B. In extended end-to-end anastomosis, greater mobilization is required, and the resection extends to the undersurface of the arch. Note how proximal the cross-clamp must be. Only the innominate artery perfuses the brain. Reprinted with permission under STM Association signatory guidelines from Jaquiss. ⁶¹

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Figure 5.

Subclavian flap repair: The subclavian artery is ligated, and the proximal portion filleted open. It is then turned over the distal portion of the aorta to enlarge the size of the isthmus. Note that the coarctation tissue is not excised. Reprinted with permission under STM Association signatory guidelines from Kouchoukos et al. ²⁴

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Figure 6.

Reverse subclavian flap repair. The subclavian artery is ligated, and the proximal portion filleted open and turned over proximally to enlarge the distal arch. A resection and end-to end anastomosis of the coarctation is then performed. The repair is described as being under less tension than an extensive end-to-end repair. Reprinted with permission under STM Association signatory guidelines from Jonas. ⁶²

Preoperative Evaluation and Management

Preoperative evaluation begins with a thorough review of the history, physical examination, current medications, and available laboratory and imaging studies. As discussed above, coarctation that presents in the neonatal period often manifests with progressive heart failure, shock, and acidosis. These infants require infusion of PGE₁ to maintain ductal patency and relax juxtaductal tissue at the coarctation site. This will improve hemodynamics and allow time for further workup with echocardiography or imaging such as CT or MRI.^18,24 Neonates must be monitored for apnea, which can occur with PGE₁ infusions and may require PGE₁ dose titration or intubation and mechanical ventilation. Inotropes and diuretic therapy may be needed in the sickest infants. Patients with more moderate aortic narrowing may be asymptomatic, and coarctation may be discovered incidentally or with the astute observation of differential limb hypertension.

Standard preoperative studies include a 12-lead electrocardiogram (ECG), chest X-ray (CXR), and TTE. ECG may demonstrate LV hypertrophy and ST-T wave abnormalities. Classic CXR findings include the “3-sign” adjacent to the transverse arch and pulmonary artery silhouette representing the coarctation site. Rib notching can be seen on ribs 3 to 9 in older children and adults with fully formed collaterals. Pulmonary edema or infiltrates may be seen in the setting of cardiogenic shock. TTE, in addition to demonstrating the coarctation and pressure gradient as discussed previously, can also give important information about ductal patency, biventricular function, pulmonary artery pressures, and the presence of any associated cardiac lesions. ²⁵ Necessary preoperative lab testing varies depending on the patient’s age, disease severity, and the proposed intervention but often includes a complete blood count, blood type and crossmatch, and electrolytes. Serial arterial blood gases and lactate may be useful to evaluate the adequacy of resuscitation in critically ill infants.

Perioperative Anesthetic Management

Anesthetic management will vary depending on whether a catheter-based intervention or surgical repair is being undertaken. For catheter-based interventions, the decision regarding general anesthesia versus sedation should take into consideration the patient’s age, clinical status, comorbidities, procedure-specific factors, and patient preference while also considering that moderate to deep sedation will usually be required to blunt the painful stimulus of aortic dilation. Inadequate anesthesia puts the patient at risk of moving during aortic dilation, which can result in significant morbidity such as misplacement of the stent, stent migration, or aortic dissection. At our institution, we routinely administer general anesthesia with a laryngeal mask airway or endotracheal tube for these procedures. Standard monitors should be placed. Non-invasive blood pressure monitoring (NIBP) must be placed proximal to the coarctation to reflect coronary and cerebral pressures, which will be the right arm in most patients. It is rare to place additional invasive arterial monitoring beyond the access that is obtained by the interventionalist. However, it should be recognized that a femoral sheath will only measure pressures distal to the coarctation and should not be used to make treatment decisions. Furthermore, the pressure will often be unavailable because the procedure itself is performed through the arterial sheath. Some adults with preexisting comorbidities, especially hypertension, benefit from a separately placed invasive arterial line inserted on the precoarctation side (on the same side as the NIBP cuff) in order to optimize management of hypertension. Close communication between the cardiologist and anesthesiologist is critical during balloon and stent expansion because this will result in a sudden and dramatic increase in LV afterload, similar to placement of an aortic cross-clamp (albeit for a much shorter duration), as discussed below. The cardiologist may elect to use rapid right ventricular pacing with a pacing catheter to reduce the aortic pulse pressure and, thus, optimize precise placement of the stent. Brief cessation of cardiac output during balloon dilation, stent placement, and rapid ventricular pacing are typically well tolerated, especially in patients with preserved LV function. After completion of the procedure, the patient can be transported to the recovery area. It is rare for the patient to require ICU admission and/or intravenous antihypertensive medication post–interventional procedure.

The remainder of this section will focus on specific considerations for surgical repair via thoracotomy.

Outcomes

Immediate hemodynamic outcomes for surgical correction versus transcatheter intervention are similar; however, percutaneous angioplasty has been associated with a higher rate of recoarctation and aneurysm formation.^56-58 Although balloon angioplasty may be safely performed in infants with a discrete narrowing and no evidence of arch hypoplasia, most will require reintervention as a result of recoarctation. ⁵⁹ Society guidelines recommend early intervention when significant coarctation is identified, with the decision between surgical correction and transcatheter intervention to be decided by a multidisciplinary team while considering the patient’s age, anatomy, and comorbidities as well as institutional expertise.^25,34,35 Long-segment coarctation, arch hypoplasia, and vessel tortuosity are less amenable to percutaneous intervention. ³⁵ For initial management of recoarctation, catheter intervention is now the uniformly recommended modality. As stated above, advances in endovascular stent technology have propelled percutaneous stent placement to be an earlier option for management of recoarctation in larger children, where the stent can be redilated to reach adult size as the patient grows.^25,34,35

Early mortality is less than 1% for primary surgical correction; however, it increases to 1% to 3% for reoperations and can be as high as 5% to 10% if there are significant comorbidities or LV dysfunction. ²⁵ Complications associated with surgical correction include bleeding, pleural effusion, recurrent laryngeal nerve injury, phrenic nerve injury, rebound hypertension, arm claudication or arm length discrepancy, recoarctation, aneurysm formation, mesenteric arteritis, and spinal cord ischemia (Figure 7).^25,35 Identified risk factors for spinal cord injury include prolonged cross-clamp times, hyperthermia, poorly developed collaterals, low proximal and distal aortic blood pressures, and elevated cerebral spinal fluid pressures. ⁴⁴ Early mortality for catheter-based interventions is less than that for surgical correction, with associated complications including recoarctation, stent migration, aneurysm formation, femoral artery injury, and rarely, stroke or aortic rupture. ³⁵

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Figure 7.

An adult patient in the catheterization lab years after a subclavian flap aortoplasty. Note the abnormal development of the patient’s right hand. This patient had a left-sided aortic arch with an aberrant right subclavian artery (RSA) and the RSA was sacrificed to incorporate into the repair.

After surgical or interventional correction of aortic coarctation, all patients should maintain at least yearly surveillance with their cardiologist and undergo aggressive management of blood pressure and other cardiovascular risk factors.^25,35 Evaluation of the repair site by MRI/CT should be considered at least every 5 years based on individual patient anatomy and comorbidities. ²⁵ These patients are at ongoing risk for accelerated coronary artery disease, hypertension, bicuspid aortic valve complications, and cerebrovascular events (from a higher rate of berry aneurysms and accelerated atherosclerosis) as well as aortic complications such as recoarctation, aneurysm formation, dissection, and rupture. ⁶⁰

Summary

Coarctation of the aorta is a common left-heart obstructive lesion. Critical coarctation usually manifests during the neonatal period and is treated with PGE₁ to maintain ductal-dependent flow to the lower body, lest the child progress to frank heart failure and shock. More moderate lesions usually manifest later in childhood or adulthood with upper-body hypertension, headache, and evidence of aortic collaterals. Uncorrected aortic coarctation leads to significant early morbidity and mortality. Perioperative management goals most importantly include supporting appropriate perfusion to all organ systems during the periods before, during, and after aortic cross-clamp. The intraoperative period is marked by dramatic fluctuations in blood pressure in vascular beds both proximal and distal to the coarctation and aortic cross-clamp, and these must be managed appropriately to limit the risk of intraoperative morbidity. Both surgery and catheter-based interventions have demonstrated safety and efficacy for the correction of aortic coarctation with significant improvements in subsequent mortality and morbidity. The choice to pursue surgical correction versus transcatheter intervention is best determined through multidisciplinary decision making. After correction, close follow-up is important because of elevated risks of recoarctation, accelerated coronary artery disease, and especially, systemic hypertension.