COARCTATION OF THE AORTA

Coarctation of the aorta comprises 5-8% of all congenital heart disease, occurring 2-5 times more often in males than females. One-third of Turner's syndrome (XO) patients has a coarctation. There is an association with a bicuspid aortic valve with a reported incidence of 30-40% or more. Other cardiac anomalies including PDA and VSD may be associated, and the most important associated noncardiac abnormality is intracerebral aneurysm.

In most cases, the constriction is located at the junction of the ductus arteriosus (juxtaductal) below the origin of the left subclavian artery. Pathological findings include medial thickening and intimal hyperplasia forming a ridge that encircles the aortic lumen. This abnormality predisoposes to dissection or rupture in the area of the coarctation.

Clinical features:

The severity and location of the coarctation will determine the age and features of the clinical presentation.

In utero, the presence of the ductus allows blood to bypass the aortic narrowing. When the PDA and PFO close, the cardiac output to the lower extremity must all go through this narrowed segment.

The major clinical manifestation is a difference in systolic blood pressures between the upper and lower extremities, while the diastolic blood pressures are usually similar. Other classic findings are hypertension in the upper extremities, diminished or delayed femoral pulses (referred to as the brachial-femoral delay), and low blood pressures in the lower extremities. If the origin of the left subclavian is distal to the narrowing, the left arm blood pressure may also be diminished. In 3-4% of cases, both the right and left subclavian arteries originate distal to the coarctation so all four extremities will have diminished blood pressures and pulses.

Severe narrowing will present in infancy with poor perfusion, metabolic acidosis, shock, dyspnea, diaphoresis, and congestive heart failure. This may be delayed until a few weeks of life when the ductus arteriosus closes. Heart failure will rarely occur outside of the neonatal period unless it is a result of long-standing hypertension as an adult.

Less severe disease can present later in childhood or even in adulthood with chest pain with exercise, cold extremities, claudication with physical activities, hypertension and headaches. An elevated blood pressure may be the only sign. There may be a systolic ejection murmur from a bicuspid aortic valve heard best at the apex, and there may be other murmurs present if there are associated heart defects. There is development of extensive collateral vessels to bypass the narrowed segment of the aorta. This may present with rib notching on radiographic exams or continuous murmurs from the collaterals. Because of the increased risk of intracranial aneurysms, patients also have a higher chance of subarachnoid or intracerebral hemorrhage.

Diagnosis:

1. Discrepancy in UE and LE blood pressure (UE > LE). Normally, the lower extremity pressures are higher.

2. Delayed or weakened femoral pulses compared to brachial or radial pulses. Palpation should be done simultaneously. Normally, the femoral pulse is felt before the radial pulse.

3. A murmur may be present over the precordium or the upper back. Usually systolic but may extend into diastole.

4. Newborns may have a discrepancy in pre- and post-ductual oxygen saturation.

5. Electrocardiogram may be normal. In the neonate with severe disease, right ventricular hypertrophy may be seen while in older patients left ventricular hypertrophy may be seen with increased voltage and ST and T wave changes over precordial leads.

6. Echocardiogram and cardiac catherization confirm the diagnosis, and are also useful in defining the patient’s cardiac anatomy and defining other anomalies. However, echocardiography is often adequate for the evaluating surgeon without need for further imaging. The only major indication for catheterization is for therapeutic intervention. Continuous wave Doppler can determine severity of coarctation by looking at the flow velocity across the coarctation. Echocardiography can also detect coarctation as early as 16-18 weeks gestation.

Therapy:

For infants in heart failure, need to stabilize with prostaglandin E1 to keep the ductus open, dopamine +/- dobutamine, correction of the metabolic acidosis, hypoglycemia, and anemia. Surgical repair is attempted once neonate is stabilized. It is rare for emergency surgery since the introduction of prostaglandin E1.

Indications for intervention in children: hypertension, heart failure, peak instantaneous pressure gradient across the gradient of more than 20 mm Hg by Doppler or catheterization, or collateral circulation on MRI. Correction of coarctation should be done in infancy or early childhood to prevent development of hypertension.

Types of surgery: Resection with end-to-end anastomosis; subclavian flap aortoplasty for infants with long-segment coarctation; bypass graft when distance to be bridged is too long for end-to-end anastomosis; and prosthetic patch aortoplasty (rarely used)

Surgical mortality <1%. Possible complications include postoperative paradoxical hypertension due to initially increased catecholamines, left recurrent laryngeal nerve paralysis, phrenic nerve injury, and subclavian steal. Recoarctation can occur as a long-term complication in 5-10% of patients.

Balloon angioplasty is an alternative treatment and should be offered to children and adults with native coarctation or recoarctation after surgery. It is not recommended in infants under 6 months of age due to high recurrence rate, though it can be used to stabilize an infant who is in critical condition, followed by surgical repair once the infant’s condition improves. Complications include immediate residual pressure gradients of >20 mm Hg (20-35%), recoarctation (especially in infants), aortic dissection, aortic rupture, aneurysm formation (5-7%), femoral artery occlusion (up to 15%). 

For patients with a weight greater than 25 kg, implantation of a stent after angioplasty can be used. This limits the risks of angioplasty with lower residual gradient and better luminal diameter. The stent can be dilated as the child grows.

Surgery and balloon angioplasty have similar recurrence rates and incidence of aneurysm formation so either can be offered to patients older than 6 months. For patients with long-segment or tortuous native coarctation, surgical repair is recommended.

After surgery, the patient should have at least yearly follow up including monitoring of blood pressure looking for systemic hypertension. Imaging of the repair site with MRI or CT at intervals of 5 years or less recommended to look for recoarctation or aneurysm formation. To rule out intracranial aneurysm, patients should undergo at least one MR or CT looking at intracranial vessels. Endocarditis prophylaxis is not recommended for patients unless surgical repair or stenting has occurred in the past 6 months.

References
1. Rao S. Coarctation of th Aorta.  Current Cardiology Reports. 2005 7:425