![]() Consequently, the right ventricle dilates while the left ventricle is pressure loaded, resulting in the ventricular size disproportion. As a result, left ventricular afterload increases and its output decreases, whereas right ventricular output increases. Narrowing of the aortic isthmus results in diversion of blood flow from the pulmonary artery to the descending aorta by way of the ductus arteriosus. The hemodynamic consequences of COA are usually tolerated well in the fetus because blood flow to the lower body and the placenta is supplied predominantly through the ductus arteriosus with only ~10% of the combined cardiac output crossing the aortic isthmus. ![]() Internally, the caliber of the isthmus is not narrowed and blood flow is not obstructed. “Pseudo‐coarctation” of the aorta refers to deformity of the aortic isthmus characterized by tortuosity but without luminal narrowing. Involvement of the thoracic and abdominal aorta and branches has been reported in Takayasu aortitis, supravalvar aortic stenosis (Williams syndrome, familial aortic stenosis, and sporadic supravalvar aortic stenosis), and midaortic syndrome. The morphology and pathophysiology of abdominal COA is different to the typical COA of the aortic isthmus in that the involved segment is often long, the aortic media is markedly thickened, and involvement of the renal and mesenteric vessels is common. Rarely, COA affects other segments of the aorta. COA is particularly common in patients with multiple left heart obstructive lesions and is part of the Shone complex. It can be seen in other more complex cardiac defects particularly when the aortic outflow is narrowed. COA is commonly associated with bicommissural aortic valve, ventricular septal defect (VSD), subvalvar and valvar aortic stenosis, and common atrioventricular canal. The commonly used echocardiographic definition determining transverse aortic arch hypoplasia in neonates is an internal diameter 50%) of associated cardiac abnormalities suggests that COA is a more complex defect than isolated narrowing of the aorta. The anatomic criteria for defining arch hypoplasia are: (i) a proximal aortic arch that measures 60% of the ascending aortic diameter (ii) a distal aortic arch that measures 50% of the ascending aortic diameter or (iii) isthmus narrowing of 40% of the descending aorta. The aortic arch is divided into three segments: (i) the proximal arch, between the brachiocephalic (innominate) artery and the left common carotid artery (ii) the distal arch, between the left common carotid artery and the left subclavian artery (known as the transverse arch) and (iii) the isthmus, between the left subclavian artery and the ligamentum or ductus arteriosus ( Figure 22.1). COA is often attributed to the presence of ductal tissue in the aortic wall which constricts the isthmus during closure of the ductus arteriosus after birth. The incidence of chromosome 22q11 microdeletion is increased in patients with interruption of the aortic arch. Particular syndromes have been associated with COA it occurs in 12% of patients with Turner syndrome (45,XO). The role of genetic factors is increasingly recognized, and more recently variations in the NOTCH1 gene have been associated with COA. This is supported by the observation that 71% of cases of aortic atresia also have COA. Abnormal flow distribution during fetal life with decreased aortic flow has long been suspected. No single etiologic cause has emerged for COA but evidence points to an interplay between genetic, environmental, and hemodynamic factors. In a prenatal series, COA constituted up to 10% of all fetal diagnoses of congenital heart disease. COA is 1.3–1.7 times more likely in males. In ~64% of patients, COA presents soon after birth, whereas in the remaining 36% it presents at an older age. The incidence of COA is approximately 36 (range 29–49) per 100,000 live births, representing the seventh most common type of congenital heart disease, or approximately 5–7% of patients with congenital heart disease. ![]() The term is also used to describe strictures of other segments of the thoracic or the abdominal aorta. Hypoplasia of the aortic arch and other associated cardiovascular anomalies are common. Great Ormond Street Hospital for Children University College London, London, UKĬoarctation of the aorta (COA) refers to narrowing of the aortic isthmus. Jan Marek, Matthew Fenton, and Sachin Khambadkone Aortic Arch Anomalies: Coarctation of the Aorta and Interrupted Aortic Arch
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