Coarctation of the aorta

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Coarctation of the aorta (CoA) refers to an area of narrowing of the aortic arch, most commonly between the left subclavian artery and the ductus arteriosus ( aortic isthmus.)^1-3 It can be classified as simple when it occurs without important intracardiac lesions and complex when it occurs in association with significant intracardiac defects.

CoA encompasses a spectrum of lesions, ranging from segmental narrowing to severe tubular hypoplasia of the whole transverse arch. In particular, tubular hypoplasia refers to a uniform narrowing of the transverse arch, whereas segmental coarctation is usually determined by a localized shelf-like lesion, often with a degree of proximal tapering of the aortic arch toward the lesion; the two lesions often are associated.

From the anatomic standpoint, discrete coarctation is characterized by a posterior eccentric fold (posterior shelf) inside the isthmus, opposite to the orifice of the arterial duct. When this closes at birth or soon afterward, it causes further narrowing of the aortic lumen.

From the embryological standpoint, two hypotheses have been proposed: the ductal tissue theory proposes that the aortic constriction is due to migration of ductal smooth muscle cell into the aorta, whereas the hemodynamic theory proposes that the coarctation results from reduced flow through the aortic arch.

5% of newborns with congenital heart disease.

In 35%–45% of cases, CoA is an isolated heart defect (above all in infant and child forms), but in the remaining 55%–65% of cases, other cardiac anomalies (VSD, aortic and mitral valve anomalies, bicuspid aortic valve, transposition of the great arteries, and DORV) are associated.^1-3 The presence of multiple left-sided obstructive cardiac lesions associated to the coarctation of the aorta has been referred to as Shone syndrome.The presence of a persistent left superior vena cava has also been reported in association with coarctation of the aorta in a certain number of cases.

Extracardiac malformations are frequently associated with CoA (25%–35% of cases): these include urinary, gastrointestinal, central nervous system, and facial anomalies. Risk of chromosomal anomalies is high, reaching 30% —mainly monosomy X, but also trisomies 21 and 18 and 22q11 microdeletion.

Even with good visualization of the fetal aortic arch, prenatal diagnosis of discretecoarctation is very difficult.^4-5 However, when associated with tubular hypoplasia of the entire arch, the US diagnosis is less difficult and can be reasonably made during the prenatal period.Sonographic findings possibly suggesting the presence of coarctation include direct and indirect signs^1-3, the latter being burdened with a significant percentage of false positives.

Indirect signs include a significant prevalence of the right cardiac sections over the left ones on the four-chamber view and of the pulmonary artery over the ascending aorta on the outflowviews and on the three-vessel view . The right ventricular-to-left ventricular width ratio has been reported as 1.69 in fetuses with CoA and 1.19 in normal fetuses. It has been reported that isolated right dominant heart in fetus is a risk factor for postnatal CoA particularly when diagnosed in the second- trimester whereas most of fetuses with this sign in the third-trimester have a normal heart after birth.⁶

Direct signs of CoA, when possible, can be gathered by assessing the three-vessel and tracheaview⁷: on this plane, the ductal arch appears significantly larger than the aortic arch. The transverse part of the aortic arch is severely reduced in size, especially if tubular hypoplasia of the whole arch is present.

On the longitudinal view of the aortic arch, the narrowing is usually located at the isthmus; if tubular hypoplasia of the whole arch is present, the entire transverse arch is elongated and narrow, and the left subclavian artery appears to arise at the junction of the ductus arteriosus with the descending aorta. However, particular attention should be paid when evaluating the aortic arch on longitudinal views in order to not mistake, in the case of severe coarctation, the prevalent and dilated ductal arch for a normal aortic arch. This is why the three-vessel and trachea view is currently the preferred option for the comparative assessment of the ductal and aortic arches. Z-scores for the measurement of the size of tha aortic isthmus, the transverse arch and the angle between the isthmus and the ductus arteriosus were proposed to improve the accurate description of this anomaly.⁸ Recently, visualization of CoA shelf and isthmal flow disturbance to distinguish hypoplastic from normal aortic arch has been reported.⁹

On color Doppler, a complete or partial inversion of the flow in the distal part of the arch and/or in the ascending aorta and a left-to-right interatrial shunt can be seen.

The use of power Doppler in longitudinal plane is preferred for for a better definition of the aortic coarctation where a typical “shelf sign” can be seen at the isthmic region.

However, it should be recalled here that prenatal diagnosis of CoA remains challenging, with a high rate of false-positive and false-negative diagnoses.^4-5

Four-dimensional echocardiography may be used to assess the discrepancy in the size of the aortic and ductal arches .

Differential Diagnosis : the marked prevalence of the right heart sections over the left on the four-chamberview, present in the critical form of coarctation, should be differentiated from hypoplastic left heart syndrome (HLHS) and from total anomalous pulmonary venous connection ( TAPVC). However, the former is characterized by a sealed or atretic mitral valve, which is mainly normal in coarctation. In addition, color Doppler confirms normal left ventricular filling in diastole and thus differentiates aortic coarctation from HLHS. As far as TAPVC is concerned, the recognition of a single pulmonary vein entering the left atrium on color Doppler rules out this diagnosis.

On the aortic arch views (transverse and longitudinal), severe coarctation should be differentiated from interrupted aortic arch (IAA): in the latter case,the aortic arch cannot be demonstrated and a malalignment VSD is almost always associated.

The overall prognosis depends on the severity of the lesion, on the presence of associated cardiac and extracardiac lesions that can significantly influence operative mortality and the life expectancy, and on correct perinatal management.¹⁰ The overall mortality rate is less than 5% for isolated CoA. In symptomatic neonatal cases with associated cardiac lesions, the mortality rate is about 20%, ranging from 2% in cases associated with VSD to 40% in cases associated with complex cardiac anomalies or when the preoperative clinical condition is poor.³ The surgical techniques commonly used are resection of the coarcted tract with terminoterminal and terminolateral anastomoses, a subclavian flap, and widened aortoplasty. Long-term follow-up studies (>five years) have reported a 20% recoarctation rate.

A detailed anatomic scan should be performed by an expert to exclude the presence of extracardiac anomalies. Karyotyping is indicated because of the high risk of chromosomal disorders. If there is a suspicion of any anomaly of the aortic arch, delivery should be planned in a tertiary referral center, in order to allow early transfer of the newborn to the pediatric cardiology unit for final diagnosis and correct neonatal management; in fact, critical coarctation of the aorta is a ductus-dependent defect.

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2. Abuhamad A, Chaoui R . Coarctation of the aorta and interrupted aortic arch. In A practical guide to fetal echocardiography, Abuhamad A, Chaoui R. (eds). Lippincot Williams & Wilkins 2010
3. Paladini D, Volpe P. Coarctation of the Aorta. In Ultrasound of congenital fetal anomalies (eds Paladini D, Volpe P). CRC Press. 2014
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5. Sharland GK, Chan KY, Allan LD. Coarctation of the aorta: difficulties in prenatal diagnosis. Br Heart J1994; 7: 70–5.
6. Head CEG, Jowett VC, Sharland GK, Simpson JM. Timing of presentation and postnatal outcome of infants suspected of having coarctation of the aorta during fetal life. Heart 2005; 91:1070–74.
7. Gardiner H, Chaoui R. The fetal three-vessel and tracheal view revisited. Seminars in fetal & neonatal medicine. 2013 Oct;18(5):261-8. .
8. Pasquini L, Mellander M, Seale A, et al. Z-scores of the fetal aortic isthmus and duct: an aid to assessing arch hypoplasia. Ultrasound Obstet Gynecol 2007;301 29:628-33.
9. Jowett V, Aparicio P, Santhakumaran S, et al. Sonographic predictors of surgery in fetal coarctation of the aorta Ultrasound Obstet Gynecol 2012; 40: 47–54
10. Paladini D, Volpe P, Russo MG, et al. Aortic coarctation: prognostic indicators of survival in the fetus. Heart 2004; 90: 1348–9.

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