Coarctation of the Aorta

Introduction

• CoA accounts for 6 to 8% of all congenital heart disease (CHD) and occurs with an incidence of 3 to 4 out of 10,000 live births. It is believed to occur more commonly in males.^2,3,4
• The underlying cause of CoA is unknown; however, a genetic basis for its development has been implicated. It is associated with other cardiovascular lesions and syndromic phenotypes.^3,4
• Most cases of CoA are discrete and localized to the aortic isthmus (the segment of aorta between the left subclavian artery and DA), although a longer segment of aortic involvement is possible.²
• The severity of the CoA determines the degree of LV pressure overload and lower body hypoperfusion.¹
• The signs, symptoms, and age at diagnosis may also be influenced by the presence of other congenital cardiac lesions.¹

Etiology

Embryology

• Morphologically, CoA is characterized by localized narrowing of the aortic lumen by a ridge of thickened and in-folded aortic wall tissue.³
• CoA is considered a diffuse aortopathy as the segment of aorta and adjacent tissue often demonstrate abnormal histology, impaired vascular properties, and inflammation.⁴
• The mechanism for development of CoA is not fully understood. Theories about its pathogenesis include:
  • Abnormal embryogenetic development³
  • Abnormal aortic development from reduced intrauterine antegrade aortic blood flow³
  • Abnormal migration of ductal tissue into the aortic wall leading to constriction of the aortic lumen with closure of the DA³

Genetic Factors

• Variations in NOTCH1, MCTP2 and FOXC1 have been identified in patients with CoA. Mutations in the NOTCH1 gene have been identified in patients with other left-sided obstructive lesions.⁴

Epigenetic Factors

• There are no known environmental factors.

Pathophysiology

• The pathophysiology of CoA depends on the severity of aortic obstruction and the presence of associated congenital cardiac defects.^1,5
• In utero, the physiologic effect of coarctation is negligible because perfusion of the abdomen and lower extremities occurs predominantly through the DA.¹
• After birth, infants with severe CoA experience an acute increase in LV afterload with closure of the DA. The following pathophysiologic changes may occur:
  • LV dysfunction, low cardiac output (CO), cardiogenic shock, left atrial hypertension, and pulmonary edema.^1,5
  • Lower body hypoperfusion, renal and hepatic dysfunction, and acidosis.³
• In neonates and infants with CoA and an intracardiac left-to-right shunt, the reduction in pulmonary vascular resistance after birth enhances left-to-right shunting and reduces distal aortic perfusion via the DA.⁵
• Patients with mild or moderate CoA develop collateral circulation around the coarctation and tolerate closure of the DA without hemodynamic compromise. LV hypertrophy is common.^3,5
  o Collateral vessels originate from the subclavian arteries and perfuse the descending aorta through intercostal, subscapular, internal thoracic, and epigastric arteries.¹

Associated Anomalies

• CoA often occurs with other forms of CHD. The most common associated lesion is a bicuspid aortic valve.^1,3,4,5
• Other forms of CHD commonly associated with CoA are distal aortic arch hypoplasia, ventricular septal defect, and patent ductus arteriosus (PDA).^1,3,5
• CoA may be seen in the setting of a constellation of left-sided obstructive lesions known as Shone’s complex (supravalvar mitral ring, parachute mitral valve, subaortic membrane, and aortic stenosis).^1,3,4,5
• CoA is the most common cardiac defect in Turner syndrome. It is also associated with PHACE, DiGeorge, Noonan, and velocardiofacial syndromes.^1,3,4,5

Diagnosis

Presentation

• The presentation of CoA depends on the patient’s age, the severity of the aortic obstruction, and the presence of other cardiac lesions.^1,5
• Patients with severe CoA present in infancy with closure of the DA. Initial signs are variable and may include feeding intolerance, tachypnea, cardiogenic shock, or cardiopulmonary arrest.^1,5
• Patients with mild or moderate CoA often present in childhood or adulthood, as perfusion distal to the coarctation is maintained by collateral circulation. These patients may present with murmur, proximal systemic HTN, or diminished femoral pulses.^1,3,5

Diagnostic Studies

• Transthoracic echocardiography (TTE) is the first-line imaging modality given its availability, safety, and ability to measure hemodynamic parameters. Two-dimensional and Doppler techniques are used to localize the lesion, measure the aortic dimensions, and estimate the degree of stenosis.^1,3,4
  • The presence of a PDA may interfere with aortic velocity measurements and complicate a diagnosis of coarctation.^1,3,4
  • A comprehensive TTE exam should be performed to identify associated cardiac and valvular abnormalities, as well as assess ventricular function.¹
• Computed tomography (CT) provides high spatial resolution of cardiac and vascular structures and allows for multidimensional reconstruction of relevant anatomy.^1,3,4 Disadvantages include the use of ionizing radiation and the risk of nephropathy from iodinated contrast.^3,4
• Cardiac magnetic resonance imaging (CMR) is the preferred modality for noninvasive diagnosis and follow-up evaluation of CoA. It is utilized for high-quality visualization of aortic anatomy and morphology, measurement of ventricular volume, mass, and systolic function, as well as delineation of collateral circulation.^1,3,4
• Cardiac catheterization is no longer the primary diagnostic modality due to advances in three-dimensional imaging techniques; however, it remains the gold standard for assessing pressure gradients across the affected segment of the aorta. A diagnosis of CoA is confirmed by a pressure gradient of greater than 20 mmHg. Pressure gradients less than 20 mmHg can be measured with CoA and collateral flow or reduced CO. Angiography is useful for defining collateral circulation, evaluating it, and planning a transcatheter intervention.^1,2,3,4

Treatment Strategies

General

• Early intervention in the treatment of CoA is indicated to prevent long-term cardiovascular complications and mortality.^1,2,3
• Indications for treatment of CoA include:
  • Supine noninvasive blood pressure (NIBP) gradient greater than 20 mmHg between upper and lower limbs^1,3
  • Peak-to-peak coarctation gradient greater than or equal to 20 mmHg^2,3
  • Peak to peak coarctation gradient lower than 20 mmHg with radiological evidence of coarctation and significant collateral flow^1,2,3
• Other indications for intervention include HTN, congestive heart failure (CHF), LV hypertrophy, and pathological blood pressure response to exercise.³
• For neonates and infants with isolated CoA, surgical intervention is recommended in the absence of contraindications. Medical optimization before intervention or operation is indicated for patients with low birth weight, prematurity, or other risk factors for surgery.⁶

Medical Management

• In the setting of severe CoA, an infusion of prostaglandin E₁ (PGE₁) is indicated to recruit or maintain ductal patency and to relax juxtaductal aortic tissue.^1,3,5
• Inotropic medications and diuretics should be administered for CHF.^1,5
• Noninvasive positive pressure ventilation or intubation and mechanical ventilation may be required for patients with apnea from PGE1, acidosis, cardiac or respiratory failure.^1,5
• Intravenous (IV) vasodilators such as sodium nitroprusside and nicardipine, as well as beta blockers such as esmolol, are used for the acute treatment of HTN.^1,5

Surgical Management

• Surgical resection of the coarctation segment (coarctectomy) and aortic anastomosis is the treatment of choice for neonates,6 infants,6 and young children with CoA.³
• Cardiopulmonary bypass (CPB) is usually not required for the surgical management of isolated CoA. Left heart bypass may be used in older children and teenagers to maintain distal perfusion during aortic cross-clamping when adequate collateralization is absent.¹
• The surgical approach depends on the patient’s age and aortic arch anatomy.
  • For neonates and infants with isolated CoA, surgical repair through a thoracotomy is indicated. Coarctectomy with end-to-end anastomosis or extended end-to-end anastomosis is performed.^3,6
  • For neonates and infants with CoA and aortic arch hypoplasia that cannot be addressed adequately through a thoracotomy, a sternotomy is preferable.⁶
  • In these patients, CPB with regional cerebral perfusion or deep hypothermic circulatory arrest is usually required.^1,6
  • Subclavian flap aortoplasty is performed less commonly due to the risk of decreased length and strength of the left upper extremity.⁶
  • In adults, CoA is often managed with resection of the affected segment and placement of an interposition graft.³

Catheter-Based Interventions

• Balloon angioplasty is a palliative strategy for neonates and infants who are at high risk for surgery. It is often avoided in patients less than 3 to 6 months of age due to the high risk of re-CoA associated with reactive ductal tissue.³
• Endovascular stenting is the treatment of choice for children weighing more than 20 to 25 kg and adults with a discrete CoA.^1,3 It is minimally invasive and has a lower risk of re-CoA or aneurysm than angioplasty alone. The stent can be repeatedly dilated as the patient grows to reach adult size.³
• Risks of stent placement include access complications due to sheath size, stent migration, embolization, occlusion of aortic branches, aortic dissection, and rupture. Additional complications include re-stenosis, stent fracture, and aneurysm.³

Anesthetic Considerations for Interventional/Surgical Management

Preoperative Evaluation

• Evaluation depends on the patient’s age, disease severity, and clinical status.¹

Labs

• Laboratory studies may include:
  • Complete blood cell count
  • Basic or complete metabolic panel
  • Prothrombin time and partial thromboplastin time
  • Arterial blood gas
  • Lactate
  • Blood type and crossmatch

Imaging/Diagnostics

• Standard diagnostic studies include1:
  • 12-lead electrocardiogram (ECG)
  • Chest radiograph
  • Transthoracic echocardiogram
• Additional studies based on patient age, severity of disease, and clinical status may include^2,3,4:
  • Head ultrasound
  • Computed tomography
  • CMR
  • Catheter angiography

Intraoperative Care

• Standard American Society of Anesthesiologists (ASA) monitors, including ECG, NIBP, pulse oximetry, and waveform capnography, are indicated for all interventions.¹
• Further choices for monitoring, access, and anesthetic technique depend on whether the intervention is catheter-based or surgical, patient age, clinical status, comorbid conditions, and institutional practices.¹

Monitoring

• Catheter-based procedure:
  • Standard ASA monitors with NIBP are placed proximal to the site of CoA (most commonly the right upper extremity) to reflect coronary and cerebral perfusion pressure.¹
  • Invasive arterial line proximal to the site of CoA is considered for patients with comorbidities, including hypertension or ventricular dysfunction.¹
• Surgical procedure:
  • The Standard ASA monitors include a pulse oximeter on the right hand, a right upper extremity invasive arterial line, and consideration for a lower extremity invasive arterial line versus an NIBP cuff and a second pulse oximeter.^1,5
  • Bilateral cerebral near-infrared spectroscopy (NIRS). Consideration for renal NIRS.^1,5,7
  • Nasopharyngeal and bladder or rectal temperature.⁵
  • Monitoring of central venous pressure may guide management in patients with poor clinical status, ventricular dysfunction, or pulmonary hypertension.

Access

• Catheter-based procedure:
  • One or two sites of large-bore peripheral IV access is usually adequate. Two sites of access provide separate lines for medication administration by bolus and infusion.
• Surgical procedure:
  • Placement of central venous access depends on a patient’s clinical condition, disease severity, and institutional practices. Central venous access is useful for administering inotropic and vasoactive medications and for resuscitation.¹
  • Peripheral IV access may be sufficient in patients with a stable clinical status, such as those presenting for elective intervention.

Anesthetic Technique

• Catheter-based procedure:
  • In the pediatric setting, general anesthesia with an endotracheal tube or occasionally a laryngeal mask airway is preferred.¹
  • Adult patients may tolerate the procedure with IV sedation, with careful attention to blunt the painful stimulation of aortic dilation.¹
  • Movement during critical phases of the procedure, such as aortic ballooning or stenting, may lead to complications, including stent migration, aortic dissection, or other vascular injury.¹
• Surgical procedure (thoracotomy):
  • General endotracheal anesthesia is performed for surgical repair. A balanced technique with high-dose opioids and low inspired concentration of volatile anesthetics is usually tolerated.⁵
  • The patient is positioned in the right lateral decubitus position for left thoracotomy.¹
  • Lung isolation with right mainstem intubation, bronchial blocker, or double-lumen endotracheal tube is often employed for surgical exposure in the left hemithorax.¹
  • Permissive hypothermia to 34 – 35°C is performed to reduce the risk of spinal cord injury or paraplegia during aortic clamping.^1,5 The need to rewarm may hinder extubation in the operating room.⁵
  • Careful monitoring of cerebral NIRS during aortic clamp application is essential to ensure adequate brain perfusion.
  • Neuraxial blockade by caudal or epidural approach, as well as regional anesthetic techniques including erector spinae plane, serratus anterior, pectoralis II, paravertebral, and intercostal blocks are options for postoperative analgesia.^1,8 Continuous infusion of local anesthetic by catheter has been shown to reduce postoperative opioid requirements.⁸ Since regional blocks with local anesthetic may confound postoperative neurologic examination, it is essential to discuss the use of these techniques with the surgeon prior to the operation.

Hemodynamic Goals

• The primary strategy in the management of patients with CoA is to maintain CO by optimizing preload, heart rate, and contractility.^1,5 It is important to avoid increases in systemic vascular resistance,⁵ which can further impair CO and tissue oxygen delivery.
• Application of the aortic cross clamp produces a sudden increase in afterload on the left ventricle; pressure beyond the clamp is simultaneously reduced. Proximal hypertension is common and may improve distal perfusion through collateral vessels. Aortic clamping is often managed with an increase in volatile anesthetics. Sodium nitroprusside should be used with caution as it may worsen spinal cord perfusion by increasing the production of cerebrospinal fluid and reducing arterial blood pressure.^1,5
• Removal of the aortic clamp causes an immediate reduction in afterload, followed by a brief period of hypotension. This is mitigated by reducing the concentration of volatile anesthetics and expanding intravascular volume in anticipation of unclamping. Bolus dosing of epinephrine, calcium, or a vasopressor may be required to support CO and treat vasodilation from return of lactic acid and carbon dioxide from distal tissue. Brief hyperventilation is also employed immediately before clamp removal.^1,5
• Careful monitoring of arterial blood pressure is critical as rebound HTN after coarctation repair is common. IV vasodilators and/or beta blockers are frequently required.^1,5

Postoperative

• Postoperative HTN is often anticipated. It is likely related to high levels of catecholamines, activation of the renin-angiotensin-aldosterone system, and altered baroreceptor response.^1,5 Patients may require a transition to oral antihypertensive medications for an extended period of treatment.
• Pain after thoracotomy is also common and may complicate the management of HTN. Multimodal analgesia is recommended.
• Immediate complications may include bleeding, pleural effusion, recurrent laryngeal nerve injury, phrenic nerve injury, and spinal cord ischemia.¹
• Long-term considerations include HTN, re-CoA, aortic aneurysm, LV hypertrophy and dysfunction, accelerated atherosclerosis, and berry aneurysm formation.^1,3,4,9
• Postcoarctectomy syndrome (PCS) is an infrequent complication of CoA repair and usually occurs 48 – 72 hours after intervention. Clinically, PCS manifests as necrotizing arteritis in mesenteric vessels and is characterized by hypertension, ileus, abdominal pain, vomiting, fever, leukocytosis and melena. Its mechanism is unknown; theories include vascular changes in response to increased pulsatile flow, circulating catecholamines, renin and angiotensin II, and reactive vasospasm leading to intestinal ischemia. PCS is treated with bowel rest and antihypertensive therapy.¹⁰
• Lifelong follow-up, including blood pressure monitoring, imaging, and monitoring of complications, is recommended.^1,3,4,9