Background
Coarctation of the aorta (CoA) is a relatively common defect that accounts for 5-8% of all congenital heart defects. Coarctation of the aorta may occur as an isolated defect or in association with various other lesions, most commonly bicuspid aortic valve and ventricular septal defect (VSD). The diagnosis of coarctation of the aorta may be missed unless an index of suspicion is maintained, and diagnosis is often delayed until the patient develops congestive heart failure (CHF), which is common in infants, or hypertension, which is common in older children. This article discusses the pathology, pathophysiology, clinical features, noninvasive and invasive evaluation, and therapy in patients with coarctation of the aorta.
Pathologic anatomy
Coarctation of the aorta may be defined as a constricted aortic segment that comprises localized medial thickening, with some infolding of the medial and superimposed neointimal tissue.
The localized constriction may form a shelflike structure with an eccentric opening or may be a membranous curtainlike structure with a central or eccentric opening. The coarctation may be discrete, or a long segment of the aorta may be narrowed; the former is more common.
In the past, coarctation of the aorta has been described as preductal (or infantile) type or postductal (or adult) type, depending on whether the coarctation segment is proximal or distal to the ductus arteriosus, respectively. However, a closer examination of the anatomy suggests that all coarctations are juxtaductal.
The classic coarctation of the aorta is located in the thoracic aorta distal to the origin of the left subclavian artery at about the level of the ductal structure. However, rarely, a coarcted segment is present in the lower thoracic or abdominal aorta. In such instances, the coarcted segment may be long and fusiform with irregular lumen; many consider these to be inflammatory or autoimmune in origin, and they may be variants of Takayasu arteritis.
Dilatation of the descending aorta immediately distal to the coarctation segment (poststenotic dilatation) is usually present. A jet lesion on the wall of the aorta distal to the coarctation site may also be present. Varying degrees of hypoplasia of the isthmus of the aorta (the portion of the aorta between the origin of the left subclavian artery and ductus arteriosus) are present in most patients with thoracic coarctation; this hypoplasia may be significant in symptomatic coarctation of the neonate and infant; in children and adults, the isthmus may have only mild narrowing. The transverse aortic arch (the arch between the origin of the right innominate artery and the left subclavian artery) is also hypoplastic in symptomatic neonates and infants. Collateral vessels that connect arteries from the upper part of the body to the vessels below the level of coarctation may be seen; these may be present as early as a few weeks to a few months of life.
The most commonly associated clinically significant defects include patent ductus arteriosus, VSD, and aortic stenosis. The earlier the infant presents, the more likely a significant associated defect is present. Bicuspid aortic valve may be seen in nearly two thirds of infants with coarctation of the aorta, whereas only 30% of those who present in childhood have such an anomaly.
Mitral valve anomalies, although less common than those of the aortic valve, are also associated with coarctation of the aorta. Sometimes, coarctation of the aorta is a complicating feature of a more complex cyanotic heart defect, such as transposition of the great arteries, Taussig-Bing anomaly, double-inlet left ventricle, tricuspid atresia with transposition of the great arteries, and hypoplastic left heart syndrome.
Aortic coarctation is extremely rare in patients with severe right ventricular outflow tract obstructions such as tetralogy of Fallot and pulmonary atresia with intact ventricular septum. Some patients with coarctation of the aorta may have cerebral aneurysms, predisposing them to cerebrovascular accidents with severe hypertension later in life. Coarctation of the aorta is the most common cardiac defect associated with Turner syndrome.
Pathogenesis
The exact mechanism by which aortic coarctation is produced is not clearly understood. The most commonly invoked hypotheses include hemodynamic and ectopic ductal tissue theories. In the hemodynamic theory, an abnormal preductal flow or abnormal angle between the ductus and aorta that increases right-to-left ductal flow and decreases isthmic flow potentiates development of coarctation. Postnatal spontaneous closure of the ductus arteriosus completes the development of aortic obstruction.
A high incidence of coarctation of the aorta in patients with congenital heart defects with decreased antegrade aortic flow in utero and virtual absence of CoA in patients with right heart obstructions lends credence to the hemodynamic theory. Abnormal extension of ductal tissue into the aorta (ectopic ductal tissue).
has been postulated to create the coarctation shelf and, with ductal closure, development of aortic obstruction. This theory, however, does not explain the variable degrees of isthmus and aortic arch hypoplasia associated with coarctation of the aorta.