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3.1 AORTIC COARCTATION

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EPIDEMIOLOGY/GENETICS

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Definition Aortic coarctation (AC) is a narrowing of the aorta; greater than 90% occur between the left subclavian artery and the ductus arteriosus (aortic isthmus). The most severe form of AC is complete interruption of the aortic arch, with most interruptions occurring between the left carotid artery and the left subclavian artery.

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Epidemiology The prevalence is 0.6 per 1000 live births and has a M2:F1 ratio. AC accounts for 7% of all congenital cardiac disease. Of AC, 32% are isolated, while the remaining 68% have additional anomalies, including cardiovascular (24%), genitourinary (20%), central nervous system (12%), and skeletal (6%) anomalies.

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Embryology There are two theories to explain the different types of AC. A preductal AC is theorized to result from decreased blood flow through the left ventricle and aorta leading to impaired growth of the isthmus. A ductal, or postductal, AC is suspected to result from ductal tissue present around the posterior aspect of the proximal descending aorta. This tissue constricts along with the ductus, causing aortic constriction.

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Inheritance Pattern The inheritance pattern is thought to be polygenic. There is a strong association with monosomy X (Turner syndrome). At least 5% of girls with coarctation may be found to have monosomy X; thus, the prevalence may be higher prenatally. The recurrence risk for isolated coarctation is 2% when one sibling is affected and 6% when two siblings are affected. The recurrence risk for congenital heart defects in offspring given one affected parent is 4% when the mother is affected and 2% when the father is affected. Coarctation also occurs in mosaic trisomy 16, DiGeorge syndrome (deletion 22q), Noonan syndrome, and many other syndromes.

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Teratogens Maternal diabetes mellitus.

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Prognosis With isolated coarctation of the aorta, surgical management generally results in a good long-term outcome. When coarctation occurs along with other, more complex intracardiac disease, it is often the associated disease that more strongly influences the prognosis. If the AC goes undetected in the newborn, severe heart failure and acidosis can occur.

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SONOGRAPHY

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FINDINGS
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  • Ultrasound identification of a discrete narrowing of the aortic arch is limited due to compensation from the ductus arteriosus.

  • Indirect signs of AC can lead to a very strong suspicion in the mid-second and early third trimester. These include the following:

    • Discrepant ventricular size with the right larger than the left. This finding is more useful in the second compared to the third trimester.

    • The ratio of the diameter of the ascending aorta to the diameter of the main pulmonary artery is a helpful clue to AC, with a normal ratio being 1.25. One study found that AC was associated with a ratio greater than 2.

    • At 14 to 16 weeks, a significant discrepancy between a large ductus arteriosus and a smaller aorta may be seen.

    • Left-to-right ...

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