Aortic Coarctation

Introduction
Background


Coarctation of the aorta is a narrowing of the aorta most commonly found just distal to the origin of the left subclavian artery. Most patients with coarctation have juxtaductal coarctation. Older terms, such as preductal (infantile-type) or postductal (adult-type), are often misleading.

Pathophysiology

The vascular malformation responsible for coarctation is a defect in the vessel media, giving rise to a prominent posterior infolding (the "posterior shelf"), which may extend around the entire circumference of the aorta. The gross pathology of coarctation varies considerably. The lesion is often discrete but may be long, segmental, or tortuous in nature.

Histology

The coarctated aortic segment reveals an intimal and medial lesion consisting of thickened ridges that protrude posteriorly and laterally into the aortic lumen. The ductus (ie, patent embryonic remnant) or ligamentum arteriosus (closed and fibrosed) inserts at the same level anteromedially. Intimal proliferation and disruption of elastic tissue may occur distal to the coarctation. At this site, infective endarteritis, intimal dissections, or aneurysms may occur. Cystic medial necrosis occurs commonly in the aorta adjacent to the coarctation site and acts as a substrate for late aneurysm formation or aortic dissection in some patients.

Embryology

Coarctation is due to an abnormality in development of the embryologic left fourth and sixth aortic arches that can be explained by 2 theories, the ductus tissue theory and the hemodynamic theory.

In the ductus tissue theory, coarctation develops as the result of migration of ductus smooth muscle cells into the periductal aorta, with subsequent constriction and narrowing of the aortic lumen. Commonly, coarctation becomes clinically evident with closure of the ductus arteriosus. This theory does not explain all cases of coarctation. Clinically, coarctation may occur in the presence of a widely patent ductus arteriosus, and it may occur quite distant from the insertion of the ductus arteriosus, such as in the transverse arch or abdominal aorta.

In the hemodynamic theory, coarctation results from reduced volume of blood flow through the fetal aortic arch and isthmus. In a normal fetus, the aortic isthmus receives a relatively low volume of blood flow. Most of the flow to the descending aorta is derived from the right ventricle through the ductus arteriosus. The left ventricle supplies blood to the ascending aorta and brachiocephalic arteries, and a small portion goes to the aortic isthmus. The aortic isthmus diameter is 70-80% of the diameter of the neonatal ascending aorta.

Based on this theory, lesions that diminish the volume of left ventricular outflow in the fetus also decrease flow across the aortic isthmus and promote development of coarctation. This helps to explain the common lesions associated with coarctation, such as ventricular septal defect, bicuspid aortic valve, left ventricular outflow obstruction, and tubular hypoplasia of the transverse aortic arch. This theory does not explain isolated coarctation without associated intracardiac lesions.
Frequency
United States

This condition represents 5-10% of all congenital cardiac lesions. It represents 7% of critically ill infants with heart disease.
Mortality/Morbidity
Patients who are not treated for coarctation of the aorta may reach the age of 35 years; fewer than 20% survive to age 50 years. If coarctation is repaired before the age of 14 years, the 20-year survival rate is 91%. If coarctation is repaired after the age of 14 years, the 20-year survival rate is 79%.
After repair of the aortic coarctation, 97-98% of patients are New York Heart Association (NYHA) class I. Impaired diastolic left ventricular function and persistent hypertrophy due to increased pressure gradient at the coarctation site during exercise may result in myocardial hypertrophy despite successful hemodynamic results. Overall, left ventricular systolic function is normal or hyperdynamic in these patients.
Pregnancy: Most women reach childbearing age. If maternal coarctation is not repaired, the risk to fetus and mother is increased. The maternal mortality rate is approximately 3-8%. Even women who have had their coarctation repaired have an increased risk of aortic dissection and rupture of a cerebral aneurysm in the third trimester and peripartum period due to hemodynamic and hormonal changes. All pregnant women with a history of coarctation, either native or repaired, should be considered high risk. Significant stenosis—native, residual, or recurrent—is a contraindication to pregnancy.
Race

Coarctation is 7 times more common in whites than Asian persons. It has a lower incidence among Native Americans than other population groups in Minnesota.
Sex

Male-to-female predominance is 1.3-2:1 in most series.
Age

Age at detection of coarctation of the aorta is dependent on severity of obstruction and coexistence of other lesions.
Clinical
History

The history of those with coarctation of the aorta includes the following.

Early life: Depending on severity of obstruction and associated cardiac lesions, patients may present with congestive heart failure, severe acidosis, or poor perfusion to the lower body.
Beyond infancy: Patients are usually asymptomatic. They may present with hypertension, headache, nosebleed, leg cramps, muscle weakness, cold feet, or neurologic changes.

Physical

The diagnosis of coarctation generally can be made on physical examination. Blood pressure differential and pulse delay are pathognomonic.

Physical appearance
Patients may appear healthy. If coarctation compromises the origin of the left subclavian artery, the left arm is smaller than normal. Otherwise, general development is normal.
In XO Turner syndrome, a condition frequently associated with coarctation, a phenotypic female has the following features: short stature, webbed neck, absent or scanty axillary and pubic hair, broad chest and widely spaced hypoplastic or inverted nipples, low posterior hairline, small chin, prominent ears, cubitus valgus, short fourth metacarpals and metatarsals, distal palmar triaxial radii, narrow hyperconvex nails, and extensive pigmented cutaneous nevi.
Arterial pulse: Abnormal differences in upper and lower extremity arterial pulses and blood pressures are clinical hallmarks of coarctation of the aorta. Pulses distal to the obstruction are diminished and delayed. This may be appreciated best by simultaneous arm and leg pulse palpation.
Auscultation
A continuous and/or late systolic murmur is best heard posteriorly over the thoracic spine. Collateral arterial murmurs are crescendo-decrescendo in shape and delayed in onset and termination because of their origins in vessels some distance from the heart. The collateral murmurs are present bilaterally.
If the patient has associated bicuspid aortic valve, an aortic ejection sound, a short midsystolic murmur, and/or early diastolic murmur of aortic regurgitation may be audible.
Associated cardiac defects
These are observed in approximately 50% of patients with coarctation.
The most commonly reported defects are left-sided obstructive or hypoplastic defects and ventricular septal defects. Bicuspid aortic valve is observed in 85% of patients. Also, aortic arch hypoplasia is commonly found in coarctation associated with intracardiac defects.
Right-sided cardiac obstructive lesions, such as pulmonary stenosis, pulmonary atresia, or tetralogy of Fallot, are observed rarely.
Extracardiac vascular anomalies
These commonly occur in patients with coarctation. A right subclavian artery that arises aberrantly from the descending aorta distal to the coarctation occurs in 5% of patients. Rarely, both subclavian arteries originate distal to the coarctation.
Berry aneurysms of the circle of Willis occur in 3-5% of patients and may result in subarachnoid bleed.
After years of coarctation, large collateral arteries develop from the upper to lower body (ie, internal mammaries connecting to external iliac arteries and spinal and intercostal arteries connecting to the descending aorta).
Hemangiomas also have been reported with coarctation.
Extracardiac nonvascular anomalies
Extracardiac nonvascular anomalies occur in 25% of patients with coarctation of the aorta. Coarctation of the aorta occurs in 35% of patients with Turner syndrome.
Abnormalities of the musculoskeletal system, genitourinary system, gastrointestinal system, or respiratory system may be observed in as many as 25% of children with coarctation. In addition, an increasing number of children have head and neck abnormalities observed by ultrasonography.
Causes

The exact etiology of coarctation of the aorta is not known.

Genetics: Coarctation is 7 times more common in white persons than Asian persons. It has a lower incidence among Native Americans than other population groups in Minnesota.
Environment: Environmental variation and seasonal variation have been suggested to influence the development of coarctation. A study has shown increased incidence of coarctation in late fall and winter births.
Gridlock mutation: In 1995, Weinstein et al discovered a recessive mutation in zebrafish that causes a focal malformation resembling coarctation in humans.1 The mutation, named gridlock, results in failure of vascular channel formation at the site where bilaterally paired dorsal aortas join together and continue posteriorly as a dorsal midline channel, the medial dorsal aorta.

http://emedicine.medscape.com/article/150369-overview