Excerpt from Aortic Coarctation

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Background

Coarctation of the aorta is a complex cardiac lesion that requires careful follow-up care through adulthood and pregnancy. Before 1944, no therapy existed for this condition. Since 1972, surgical repair has decreased the mortality rate from 65% to 35%. In the new millennium, we hope to treat coarctation of the aorta with minimal mortality and decreasing morbidity, and without opening the chest.

Definition

Coarctation of the aorta is a narrowing of the aorta most commonly found just distal to the origin of the left subclavian artery.

Classification

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.

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