Aortopulmonary window (AP window) is a very rare congenital cardiac defect causing a communication between the aorta and pulmonary artery. The resultant left to right shunt causes volume overload to the pulmonary circulation and subsequently congestive heart failure, pulmonary hypertension, and pulmonary vascular obstructive disease if left untreated.
An aortopulmonary window can occur in isolation or, in up to 50% of cases, in association with other cardiac defects, including interrupted aortic arch (most frequent), coarctation of the aorta, transposition of great vessels, and tetralogy of Fallot. Variation of pulmonary arteries, head and neck vessels and coronary have been described in association with this defect. Although considered a conotruncal defect, DiGeorge syndrome is not associated with AP window.
Aortopulmonary window is a very rare defect accounting for 0.2% to 0.6% of all congenital malformation. There is a male preponderance. No specific genetic abnormalities have correlations with AP window, although Berry syndrome, a combination of AP window, interrupted aortic arch, and right pulmonary artery originating from the aorta is a defined entity.
The aortopulmonary septum forms at nine weeks during embryonic life. The aortopulmonary septum spirals and divides the truncus arteriosus into two great vessels, aorta and pulmonary artery. A deficiency in the aortopulmonary septum results in the AP window. These defects can vary in size and position. A defect that is away from the aortic valve is termed type I. The defect can be proximal, closure to the aortic valve, which is termed type II. A defect involving the whole length of aortopulmonary septum termed as type III. These defects tend to be larger with increased pulmonary blood flow with the onset of early pulmonary obstructive vascular disease if ever left untreated. There are some cases where the AP window may be restrictive and has presented in adult life, which can undergo successful repair. The Society of Thoracic Surgeons has recommended a fourth subtype, the “intermediate defect,” where a smaller and central defect is present with a surrounding circumferential rim of tissue.
The physiology of AP window resembles that of a large patent ductus arteriosus (PDA) or ventricular septal defect (VSD), and the degree of shunting is dependent on the size of the defect and the ratio of systemic and pulmonary vascular resistances. Postnatally, once the pulmonary vascular resistance falls, there is increased pulmonary blood flow and early onset of pulmonary over circulation. Chronic volume overload may cause pulmonary vascular changes early; hence it is imperative that these lesions are recognized early and treated early in life. Moreover, aortic arch obstruction, when present, further increases the left to right shunt. In this case, ductal closure will further decrease perfusion to the lower body and increase pulmonary overcirculation.
Aortopulmonary windows can induce the early onset of pulmonary overcirculation. Signs of pulmonary overcirculation include increased work of breathing, tachypnea, difficulty gaining weight, and chest retractions. The severity of the signs and symptoms vary as per the fall in the pulmonary vascular resistance. If the AP window is associated with an interrupted arch, symptoms usually start around 2 to 3 weeks of life, owing to ductal closure.
The infant may repent in extremis with poor feeding, cold and clammy extremities, poor systemic circulation, reduced urine output, and diminished femoral pulses. On examination, one may find signs of congestive heart failure such as tachypnea, a diaphoretic child with hepatomegaly. Pulses may be bounding due to run off into the lungs. A murmur may rarely be audible. A mid-diastolic rumble may be heard along the apex, indicating volume overload to the left side of the heart.
Diagnostic evaluation either when the infant presents in extremis or due to respiratory distress. A chest X-ray would show increased pulmonary vascular markings with mild to moderate cardiomegaly. The absence of the aortic knuckle and prominence of the main pulmonary segment may explain other subtle findings on chest X-ray. The electrocardiogram is very non-specific and may show deep Q waves in lateral precordial leads owing to increased pulmonary blood flow.
The echocardiogram is diagnostic of the AP window and also can identify associated anomalies. A 2D-echocardiography can detect the lack of wall or fallout between the aorta and pulmonary artery best visualized in subcostal and short-axis parasternal views (Video 1,2). The differentiating feature from truncus arteriosus is that the AP window has two well-formed semi-lunar valves. Due to volume overload to the main pulmonary artery, the left atrium and left ventricle may be enlarged. The descending aorta shows a diastolic reversal of flow due to run off into pulmonary arteries. Additional abnormalities such as coarctation of aorta and origins of branch pulmonary arteries require evaluation. Ventricular septal defects may be present in rare instances in addition to the AP window. In the late presentation of the AP window, echocardiographic features of elevated pulmonary vascular resistance can be appreciated.
A diagnostic cardiac catheterization should be performed to assess for pulmonary vascular reactivity in late presentations of the AP window. Cardiac catheterization would reveal equal systemic pressures both in the aorta and pulmonary artery. Left atrial pressures would appear elevated, and there would be an increase in pulmonary blood flow.
The definitive management in the AP window would be corrective cardiac surgery, which is performed typically in the neonatal period. Medical management of the congestive heart failure is an option if the patient's conditions are conducive to perform corrective surgery. Earlier surgeries can prevent irreversible changes in the pulmonary vasculature. Surgical techniques are quite simple in isolated defects, which involves division and separation of the great vessels with patch closure of the defect.
The surgical approach involves cardiopulmonary bypass and median sternotomy. Surgical outcomes are excellent with 10-year freedom from cardiac re-operation, reaching up to 100% in an isolated AP window. The surgeon also repairs associated defects concomitantly. Re-operations may be necessary to address issues such as re-coarctation. Catheter closure of smaller defects has also been described in isolated case reports.
Aortopulmonary window has a similar presentation as truncus arteriosus, large VSD, and large PDA. A diastolic reversal of flow can also be present with truncus arteriosus and large PDA. 2D-echocardiography can identify and differentiate between a variety of these defects. Large pulse pressures are present in the aortic pressure estimation due to diastolic runoff. Angiograms identify the defect between the aorta and pulmonary artery. Pulmonary vaso-reactivity testing should take place to identify suitable surgical candidates.
Diagnosis and management of the AP window require interprofessional input from different teams. Fetal cardiologists, perinatal providers, pediatric cardiologists, and pediatric cardiac surgeons play an essential role in the diagnosis and management of these defects. Lifelong follow-ups are often necessary for complex AP window patients to identify residual lesions and further management of these lesions. After a successful repair, a sizeable percentage of patients have normal physical and echocardiographic of the heart and live a completely productive life with no exercise limitations.
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