Coarctation of the Aorta

Introduction

Coarctation of the aorta comprises 5-8% of all congenital heart disease, occurring 2-5 times more often in males than females. Mean age for repair of a significant coarctation is around 17 years of age, thus detection by general pediatricians is very important.

http://en.wikipedia.org/wiki/Coarctation_of_the_aorta : Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

One-third of Turner's syndrome (XO) patients have 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.

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.

Location

There are three type of aortic coarctations:

Schematic drawing of alternative locations of a coarctation of the aorta, relative to the ductus arteriosus. A: Ductal coarctation, B: Preductal coarctation, C: Postductal coarctation. 1: Aorta ascendens, 2: Arteria pulmonalis, 3: Ductus arteriosus, 4: Aorta descendens, 5: Truncus brachiocephalicus, 6: Arteria carotis communis sinistra, 7: Arteria subclavia sinistra
http://en.wikipedia.org/wiki/Coarctation_of_the_aorta

1. Preductal coarctation (B):
   The narrowing is proximal to the ductus arteriosus. Blood flow to the aorta that is distal to the narrowing is dependent on the ductus arteriosus; therefore severe coarctation can be life-threatening. 
2. Ductal coarctation (A):
   The narrowing occurs at the insertion of the ductus arteriosus. This kind usually appears when the ductus arteriosus closes.
3. Postductal coarctation (C):
   The narrowing is distal to the insertion of the ductus arteriosus. This type is most common in adults. It is associated with notching of the ribs (because of collateral circulation),  hypertension in the upper extremities, and weak pulses in the lower extremities.

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, there is a need to stabilize them with prostaglandin E1 to keep the ductus open, and pressor support as needed with dopamine +/- dobutamine.  Correction of electrolyte abnormalities is important (i.e., metabolic acidosis, hypoglycemia).  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.

Surgical mortality is <1% and recoarctation can occur as a long-term complication in 5-10% of patients.

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 MRI 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. Bruce, C.J., and Breen J.F. (2000). "Aortic coarctation and bicuspid aortic valve." NEJM, 342. 
2. Kenny, D., and Hijazi, Z.M. (2012). "Coarctation of the aorta: from fetal life to adulthood." Cardiology Journal, 18(5), 487-495.
3. Rao, S. (2005). "Coarctation of the aorta".  Current Cardiology Reports: 7(425), 425-434.