Aortopulmonary (AP) window is a rare congenital heart defect resulting from abnormal separation of the common arterial trunk into the aorta and pulmonary artery [1–6]. An AP window is found in 0.2% of patients with congenital heart disease [2]. A variety of terms have been applied to this defect, including AP fistula, aortic septal defect, AP septal defect, and AP fenestration. A closely related defect is origin of a pulmonary artery (either the right or the left) from the ascending aorta. Although the term hemitruncus has been used for aortic origin of a pulmonary artery, this term is inaccurate and should therefore be avoided.

Historical Aspects

AP window was first described by Elliotson in 1830 [4]. Cotton [5] reported the first case in the United States in 1899. Abbott’s [6] classic review of 1000 cases of congenital heart disease included only 10 cases of AP window. In 1948, Gross [7] successfully ligated an AP window in a patient undergoing thoracotomy for closure of a patent arterial duct, but noted that this surgical approach would be dangerous in many patients. Scott and Sabiston [8] also described a closed method for division of AP window. In 1957, Cooley and associates [9] reported the first successful division of AP window during cardiopulmonary bypass. A variety of techniques [2, 8–23], have since been described for repair of AP window (Table 19.1).

Aortic origin of a pulmonary artery was first reported by Fraentzel [24] in 1868. Armer and associates [25] in 1961 reported the first successful repair of aortic origin of the right pulmonary artery by means of an interposition graft. Kirkpatrick and colleagues [26] in 1967 reported the first successful repair.

Embryology and Anatomy

During normal development, a protrusion from the dorsal wall of the aortic sac grows into the lumen of the distal outflow tract in oblique fashion, growing so as to separate the origins of the arteries of the fourth from the sixth pharyngeal arches. As it grows into the distal outflow tract, it becomes an embryonic AP septum [27]. If development proceeds normally, the protrusion approaches the distal end of the cushions within the remainder of the outflow tract, which are separating its intermediate and proximal components. Just before the protrusion fuses with the distal end of the cushions, which by this stage have also fused with each other to separate the developing aortic and pulmonary roots, it is possible to recognize an embryonic aortopulmonary foramen (Figure 19.1). It is failure to close this foramen during subsequent development that produces the window in postnatal life. It is likely that eccentric growth of the protrusion can leave either of the right or left pulmonary arteries, which take their origin from the sixth arch arteries close to the floor of the aortic sac, in continuity with the intrapericardial component of the aorta. This accounts both for overriding of the right pulmonary artery in association with persisting AP window, or anomalous origin of one pulmonary artery from the intrapericardial aorta [28, 29].

Most commonly, the window is a single defect beginning a few millimeters above the arterial valves on the left wall of the aorta [3, 27, 30]. Both the window and direct aortic origin of a pulmonary artery are associated with two normal arterial valves, thus differentiating these defects from common arterial trunk. The window itself can be very small, or as large as several centimeters in diameter. Aneurysmal dilatation may be seen in large defects. There is usually minimal length to the defect, as the term window implies, although tubular windows are described, including spiral variants [29].

Either the right or left pulmonary artery may arise from the ascending aorta [31, 32]. Such direct origin from the intrapericardial aorta should be differentiated from extrapericardial origin via either a persistently patent arterial duct, or systemic‐to‐pulmonary collateral arteries. The anomalously arising pulmonary artery, most commonly the right, usually originates from the posterior aspect of the ascending aorta a short distance above the sinotubular junction. The anomalous pulmonary artery is usually found on the opposite side to the aortic arch, with no communication found between the ascending aorta and the pulmonary trunk.

Various numeric classifications have been proposed for classification of the different types of window [2, 21, 33]. In essence, the defect can be small, intermediate in size, or large (Figure 19.2). It is this approach that is used in the Congenital Heart Surgery Nomenclature and Database Project [21]. Aortic origin of either pulmonary artery is classified as a separate defect.

The window is frequently found as an isolated defect. Associated cardiac lesions, including patency of the arterial duct [34], interruption of the aortic arch [35–37], ventricular septal defect [38], and tetralogy of Fallot [39], are present in up to one‐half of patients. Unlike the common form of interrupted aortic arch, the ventricular septum usually is intact in the setting of the window. Subaortic obstruction is rare in these patients. Diversion of aortic blood into the pulmonary circulation during fetal life, with decreased flow to the arch, has been proposed as the cause of this combination of defects. When a window is found in association with interruption of the aortic arch, the interruption is usually at the isthmus. This was found in two‐thirds of one large review, with one‐sixth having interruption between the left common carotid and left subclavian arteries. The site of interruption was not described in the remaining cases [35]. When there is type B interruption, then an associated ventricular septal defect is more common. Other associated anomalies include atrial septal defect and systemic venous anomalies. The association with tetralogy of Fallot is unusual, and the diagnosis can be difficult [39]. The left‐to‐right shunt through the window may provide adequate palliation until the development of significant pulmonary vascular disease. The presence of a right aortic arch may indicate the presence of tetralogy of Fallot. The ventriculo‐arterial connections are usually concordant, but a window has been described with discordant ventriculo‐arterial connections [40]. Anomalous origin of either coronary artery from the pulmonary trunk is another significant association [38, 41–44]. The orifice usually is found within a few millimeters of the window. Unlike the situation for isolated origin of a coronary artery from the pulmonary trunk, the coronary artery is exposed to aortic pressure and oxygenated blood. Thus, myocardial ischemia is not present, and shunting through the coronary artery does not occur. A left pulmonary artery sling has also been described in association with a window [45]. In this patient, although narrowed by external compression, the airway was left untreated as no segmental stricture was found [45]. In rare instances, the window can be found in association with extracardiac anomalies, including the VATER complex (vertebral defects, imperforate anus, tracheoesophageal fistula with esophageal atresia, and radial and renal dysplasia). Despite the frequency of association between the window and interrupted aortic arch, no consistent association has been found with DiGeorge syndrome, although persistence of the window almost certainly implies an abnormality in migration of cells from the neural crest [1]. Direct origin of a pulmonary artery from the intrapericardial aorta can also occur as an isolated defect. Nonetheless, as with the window, associated anomalies may be present, including patency of the arterial duct, interrupted aortic arch, ventricular septal defect, atrial septal defect, and tetralogy of Fallot.

Clinical Features and Natural History

The physiology of AP window is similar to that of patent arterial duct, ventricular septal defect, and common arterial trunk. The magnitude of the shunt is related mainly to the size of the defect and to pulmonary vascular resistance. Small defects are associated with small left‐to‐right shunts and minimal or no symptoms. The defect often is large, and a marked left‐to‐right shunt is present, resulting in congestive heart failure, pulmonary hypertension, and early development of pulmonary vascular obstructive disease. Cyanosis usually is absent unless severe pulmonary vascular disease has developed, but poor feeding, delayed growth, and repeated respiratory infections are frequently present. At cardiac examination, the heart is enlarged, and a systolic murmur frequently is heard in the third or fourth left intercostal space. Unlike patients with patent arterial duct, a continuous murmur is unusual. The peripheral pulses are bounding. The clinical course is thought to be similar to that of untreated patients with large ventricular septal defect; however, the shunt during diastole (at the expense of systemic and coronary perfusion) may produce earlier symptoms in patients with AP window. Patients with a large AP window usually do not survive infancy. Children and young adults with AP window are occasionally encountered and frequently have congestive heart failure, gradual development of irreversible pulmonary hypertension, and death by Eisenmenger syndrome. Le Bret and colleagues [46] report a case of a patient diagnosed late at age 17 with an AP window considered irreparable due to severe pulmonary hypertension, who then presented at 31 years of age with acute dissection and rupture of the pulmonary artery.

Aortic origin of a pulmonary artery also results in a large left‐to‐right shunt and exposes the lung to systemic pressure. The contralateral lung receives the entire right ventricular output. Pulmonary vascular disease may develop at an early age, particularly in the lung exposed to systemic flow. Of interest is that pulmonary hypertension usually is present in the contralateral lung.

Diagnosis

The differential diagnosis of AP window and aortic origin of a pulmonary artery includes patent arterial duct, ventricular septal defect, persistent common arterial trunk, and ruptured aneurysm of the sinus of Valsalva. The chest radiograph usually reveals cardiomegaly and increased pulmonary vascularity. Echocardiography can show the location and size of the defect (Figure 19.3) and is useful for evaluation of associated anomalies [47, 48

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