Definition

Coarctation refers to a stenosis of the proximal descending thoracic aorta that is almost always opposite the insertion of the ductus arteriosus—that is, at the junction of the distal aortic arch and the descending aorta just below the origin of the left subclavian artery (Fig. 38-1).¹^–⁴

FIGURE 38-1 Diagram of aortic coarctation showing narrowing of the proximal descending aorta (arrow) just below the level of the left subclavian artery.

Prevalence and Epidemiology

Coarctation of the aorta occurs in 3.2 of 10,000 births and accounts for 5% to 10% of all cases of congenital heart disease.¹^–⁴ Coarctation is more common in white males than in white females, with a male-to-female ratio of 1.3 to 2.0 : 1.³ Most cases are sporadic, but there may be a genetic inheritance.

Coarctation is thought to be the result of a malformation of the aortic media, leading to a posterior infolding or shelf.^1,^5,⁶ Most often, the shelf is discrete and opposite the ductus arteriosus. However, the malformation may be a long segment and circumferentially surround the aorta. In the latter form, there is typically diffuse tubular hypoplasia of the transverse arch and isthmus.^1,^7,⁸

Histologic examination shows thickened intima and media that protrude posteriorly and laterally into the aortic lumen. The ductus arteriosus or ligamentum arteriosus inserts anteromedially at the same level.¹

The physiologic changes in cardiovascular function vary with the severity of the coarctation (severe or mild) and the presence of associated anomalies. In critical or severe coarctation, impedance to left ventricular outflow increases. The resultant hemodynamic changes include diminished stroke volume, increased left ventricular end-diastolic pressures, and elevated left atrial pressures. If there is associated aortic stenosis or a large ventricular septal defect, left ventricular systolic pressure and end-diastolic volume will further increase. The end result is heart failure and pulmonary edema. In addition to cardiac abnormalities, there are changes in vascular physiology. The diminished perfusion of the distal aorta and lower body leads to renal failure and bowel ischemia.

In milder forms of coarctation, the left ventricular myocardium hypertrophies to normalize myocardial wall stress and maintain normal systolic ventricular function. Left ventricular ejection fraction is often normal to increased. Collateral vessels also develop, which act as a source of lower body perfusion and help maintain normal flow to abdominal viscera.¹

MANIFESTATIONS

Clinical Presentation

Critical or severe coarctation manifests in the first few days to first week of life. Symptoms include cyanosis (especially of the lower body), heart failure, shock, multiorgan failure and necrotizing enterocolitis.¹^–⁵

Milder forms of coarctation manifest later in life. Because left ventricular function is maintained and cardiac outflow is good, patients come to clinical attention because of hypertension or a heart murmur related to a bicuspid aortic valve.¹^–⁴ Blood pressure in the upper extremities is typically higher than that in the lower extremities. However, if there is an aberrant right subclavian artery, the pressure in the right upper arm may be equal to or lower than that in the left upper arm.

Imaging Studies

Indications and Algorithm

Imaging is performed to confirm the site, morphology and severity of the coarctation, extent of associated collateral circulation, any associated valvular lesions, and degree of left ventricular hypertrophy. The initial imaging examination is usually chest radiography and echocardiography. In uncomplicated cases, computed tomography (CT) or magnetic resonance imaging (MRI) is the study used to follow chest radiography to confirm the diagnosis of coarctation.

The identification of collateral flow is important in surgical planning. The aorta is cross-clamped during surgical repair if collateral flow is sufficient for lower body perfusion. If collateral formation is inadequate, the use of cardiopulmonary bypass for perfusion of the lower body may be indicated.

Techniques and Findings

CT angiography is performed with a pulmonary embolism protocol using thin collimation (<1 mm), pitch lower than 1.5,⁹^,¹⁰ fast scan time, and a single breath-hold, when possible. In adolescents and adults, contrast medium is injected via a power injector at a high flow rate of 3 to 4 mL/sec using a contrast volume of 100 to 150 mL (280 to 320 mg I/mL). Scan delay time can be determined with an automatic bolus tracking system with the cursor over the aortic isthmus or empiric timing. Empiric timing, using a delay of 20 to 25 seconds after the start of the injection, is a default method if the bolus tracking fails to trigger. Electrocardiographic (ECG) gating is not needed for the evaluation of coarctation.

The volumetric data are reconstructed at 3- to 5-mm slice thickness for routine viewing and at 1- to 2-mm slice thickness for multiplanar reformatting and three-dimensional reconstructions. A standard reconstruction algorithm is used for reconstruction.