Abstract
Aortopulmonary (AP) window is a very rare congenital heart disease resulting from a defect in the shared wall between the great arteries during embryogenesis. There are four major types of AP window based on the latest accepted classification by the Society of Thoracic Surgeons Congenital Heart Surgery Database Committee. Hemitruncus is a misnomer because there are two semilunar valves in this lesion, and it should be correctly termed as the anomalous origin of the right (more common) or left pulmonary artery from the ascending aorta. AP window and anomalous branch pulmonary artery from ascending aorta lead to a left-to-right shunt. The patients present with symptoms of congestive heart failure and will develop pulmonary hypertension and pulmonary vascular obstructive disease if left untreated. Echocardiography remains the main diagnostic modality in detecting and defining these lesions. Cardiac computed tomography, magnetic resonance imaging, and cardiac catheterization can provide additional information in selected cases. Medical management includes treating the heart failure symptoms using medications. Transcatheter closure is feasible in selected cases. Surgical repair using patch closure is the preferred treatment and should be done early to avoid the development of pulmonary hypertension. Pulmonary hypertensive crisis can complicate the immediate postoperative care. Long-term survival as well as late results of surgical correction of AP window without associated anomalies is excellent.
Key words
Aortopulmonary window, Hemitruncus, Pulmonary Hypertension, Cardiac defect, Congenital, Congenital Cardiac Surgery, Anomalous
Epidemiology
Aortopulmonary (AP) window, also known as AP septal defect, is a persistent communication between the walls of the intrapericardial aorta and pulmonary trunk due to failure of closure of the embryonic AP foramen. AP window was first described by J. Elliotson in 1830. This abnormality occurs during septation of the truncus arteriosus into the pulmonary artery and aorta and is associated with two separate semilunar valves. It is a rare congenital anomaly representing only 0.1% to 0.2% of all congenital heart disease. Some studies have shown a male preponderance (2 : 1). It is associated with additional congenital heart anomalies in approximately 50% of cases, the most common being an interrupted aortic arch (IAA). The first successful surgical closure of AP window was reported by Robert Gross in 1952.
Classification
According to the classification by Mori et al., there are three subtypes of AP window. Type I consists of a proximal defect close to the sinotubular junction, with very little inferior rim above the semilunar valves. Type II defines a distal defect toward the margins of the pericardial reflection, with absence of a superior rim at the pulmonary artery bifurcation. Type III refers to a large defect that extends from the semilunar valves to the pulmonary artery bifurcation. In 1979 Richardson et al. proposed a classification similar to Mori’s classification. Types I and II remained the same. The Richardson type III describes the anomalous origin of pulmonary artery (AOPA) directly from the ascending aorta. This type is erroneously referred to as “hemitruncus” but is no longer recognized as a morphologic variant of truncus arteriosus because there are two semilunar valves. The Society of Thoracic Surgeons Congenital Heart Surgery Database Committee accepted the original Mori classification with the addition of a fourth subtype, an “intermediate” defect, consisting of a smaller, central defect with a circumferential rim of tissue, and proposed that aortic origin of either pulmonary artery be classified as a separate defect ( Figs. 54.1 to 54.4 ).
Embryology
The septum dividing the truncus is formed proximally by the fusion of the distal right and left truncal wall cushions forming two channels (aortic and pulmonary) and distally by the contributions from the fourth and sixth aortic arches. The aortic channel aligns distally with the fourth arch to form the aorta, and the sixth aortic arch aligns with the other channel to form the pulmonary artery. This results in complete septation of the truncus arteriosus with separate aorta and pulmonary artery and with two separate semilunar valves. AP window and anomalous origin of pulmonary artery from the aorta occur due to deficiency in the septation of the truncus arteriosus during embryologic development.
Some authors have suggested that it is incorrect to describe the lesions as “aortopulmonary septal defects” due to the separate nature of formation of the walls of the intrapericardial arterial trunks. There is no known stage in embryogenesis, with a complete septum formed between the cavities of the arterial trunks. Hence, the AP window is described as a persistence of the embryonic AP foramen from a failure of fusion of distal cushions with each other, or the arterial spine formed from the fourth and sixth aortic arches.
Proximal AP window (type I) can occur due to failure of fusion of the truncal wall cushions, whereas distal defect (type II) and AOPA can result from abnormal migration of the sixth aortic arch.
Morphology
AP window is most commonly a single communication between the intrapericardial portions of the aorta and the pulmonary artery and usually is located a few millimeters above the two separate semilunar valves. It may be round, oval, or spiral and may vary in size from a few millimeters to over a centimeter. It is characterized by the presence of proximal separate walls of aorta and pulmonary artery with two distinct roots.
In AOPA a single pulmonary artery (most commonly the right pulmonary artery) arises anomalously from the ascending aorta, most often from the posterior or posteromedial aspect of the ascending aorta, a short distance above the sinotubular junction. This anomaly is associated with two separate semilunar valves, and therefore the term hemitruncus is misleading because this is not a lesion with a common arterial “trunk” but rather simply an anomalous origin of a branch pulmonary artery from the aorta.
Associated Lesions
Additional congenital heart lesions are present in up to 50% of patients with AP window and commonly are related to obstruction to systemic or pulmonary outflow. The most common associated defect is interrupted aortic arch (most commonly type A). The combination of distal AP window, AOPA, intact ventricular septum, and IAA is described as Berry syndrome.
- 1.
Some other commonly associated lesions that have been reported include patent ductus arteriosus, septal defects, Tetralogy of Fallot, coronary abnormalities, and transposition of great arteries.
- 2.
AP window has also been reported with extra cardiac anomalies as part of the VATER association (vertebral defects, imperforate anus, tracheoesophageal fistula with esophageal atresia, radial and renal dysplasia.
- 3.
The spectrum and frequency of association of cardiovascular lesions with AP window was well studied by Bagtharia et al as shown in Table 54.1 .
TABLE 54.1
Associated Spectrum of Congenital Cardiovascular Anomalies With Aortopulmonary Window
Anomaly
n
% of All Patients
Anomalies of aortic arch
21
51
Interrupted aortic arch at isthmus
5
12
Interrupted aortic arch between left common carotid and left subclavian artery
1
2
Aortic coarctation
4
10
Aortic isthmal hypoplasia
3
7
Aortic atresia
1
2
Right aortic arch
4
10
Double aortic arch
1
2
Anomalous origin of right subclavian artery
1
2
Left subclavian artery from pulmonary trunk
1
2
Ventricular septal defect
7
17
Atrial septal defect
15
36
Patent arterial duct
16
38
Anomaly of pulmonary outflow
8
19
Stenosis of pulmonary arteries
3
7
Tetralogy of Fallot (1 with nonconfluent pulmonary arteries)
2
5
Pulmonary valvar stenosis
1
2
Aortic origin of right pulmonary artery
1
2
Isolated left pulmonary artery from duct
1
2
Left ventricular outflow obstruction
4
10
Subaortic stenosis
3
7
Aortic valvar stenosis
1
2
Persistent left superior caval vein to coronary sinus
3
7
Superior-inferior ventricular relationship
2
5
Coronary arterial anomaly
2
5
Right coronary artery from pulmonary trunk
1
2
Absent left coronary orifice
1
2
Mitral valvar and pulmonary venous stenosis
1
2
Modified from Bagtharia R, Trivedi KR, Burkhart HM, et al. Outcomes for patients with an aortopulmonary window, and the impact of associated cardiovascular lesions. Cardiol Young . 2004;14(5):473-480
- 4.
Of note, Tetralogy of Fallot can be difficult to diagnose because AP window allows a significant amount of blood to shunt into the pulmonary circulation, providing adequate palliation for tetralogy of Fallot until significant pulmonary vascular disease develops. Right aortic arch is commonly present in patients with AP window with tetralogy of Fallot, and the presence of a right aortic arch with AP window should alert providers to rule out tetralogy.
Extracardiac anomalies associated with AP window have rarely been reported with VATER association (vertebral defects, imperforate anus, tracheoesophageal fistula with esophageal atresia, radial and renal dysplasia).
The AOPA may be associated with AP window, as mentioned above, or may individually be associated with other cardiac anomalies such as PDA, IAA, septal defects, and Tetralogy of Fallot.
Physiology
The left-to-right shunt across the AP window depends on the size of the defect and the relative resistances in the pulmonary and systemic circuits. This physiology is similar to that found in PDA but differs from PDA because AP window generally causes flow reversal in the entire thoracic aorta and not just the descending aorta ( Figs. 54.5 and 54.6 ). This diastolic runoff can have deleterious consequences on both systemic and coronary perfusion.
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