Aorto-Pulmonary Window

Summary: An aortopulmonary window results from a developmental defect in the septum that normally separates the aorta and the pulmonary artery during the division of the arterial trunk. This creates a large communication directly between the ascending aorta and the main pulmonary artery, located above the aortic and pulmonary valves. The pathophysiology is similar to that of a very large PDA, involving a large arterial shunt with significantly increased pulmonary blood flow. Clinically, affected infants often present with early cardiac failure, poor weight gain, and significant left heart dilation. Diagnosis can be antenatal or postnatal via echocardiography. When echo shows significant left heart dilation but no PDA or large ventricular septal defect (VSD), clinicians should actively look for an aortopulmonary window. The left ventricle is usually hyperkinetic. Early surgical closure with a patch is essential, ideally before two months of life. This is critical because pulmonary vascular resistance can fix very early in these cases, leading to irreversible pulmonary hypertension (Eisenmenger syndrome). Post-operative monitoring for pulmonary hypertensive crises is crucial.

Review

Aortopulmonary window (APW) is a rare congenital heart defect characterized by an abnormal communication or opening between the intrapericardial components of the ascending aorta and the main pulmonary trunk. This occurs in the presence of two distinct, patent arterial (semilunar) valves arising from separate subaortic and subpulmonary outflow tracts. It is distinguished from common arterial trunk by the presence of these two separate valves. APW is considered a rare congenital heart lesion, accounting for only 0.1% to 0.6% of all congenital heart malformations. The embryological basis for APW is thought to be a failure of fusion of the embryonic aortopulmonary foramen during the developmental separation of the aorta and pulmonary trunk. This involves incomplete fusion of the proximal central cushions.

APW defects can vary in size, from a few millimeters to a large opening. They are typically located between the left lateral wall of the aorta and the right wall of the pulmonary trunk. A common classification system, proposed by Mori et al., divides APW into three types based on location: 

• Type I (proximal, above the sinuses of Valsalva), 

• Type II (distal, near the origin of the right pulmonary artery), and 

• Type III (total, involving most of the ascending aorta and pulmonary trunk). 

• Recent studies often report Type I as the most common, followed by Type III and then Type II.

APW may occur as an isolated lesion, but it is frequently associated with other congenital cardiac abnormalities. The reported association rate varies, but some sources indicate it occurs with other defects in one third to half of cases, while a recent study found associated lesions in 90% of cases. Common associated lesions include arch abnormalities, specifically interrupted aortic arch (IAA) and coarctation of the aorta (CoA). IAA, when associated with APW, is nearly always Type A and is generally not linked to DiGeorge syndrome, suggesting APW may be distinct from conal septum abnormalities seen in some other arch defects. Other associated defects include ventricular septal defect (VSD), atrial septal defect (ASD), patent ductus arteriosus (PDA), anomalous origin of a coronary artery (particularly the right pulmonary artery from the ascending aorta), Tetralogy of Fallot, and Transposition of the Great Arteries (TGA). Anomalous coronary arteries, including ARCAPA (anomalous right coronary artery from pulmonary artery) and coronary fistulas, are rare but recognized associations. A specific rare combination of distal APW, IAA (usually Type A), and aortic origin of the right pulmonary artery is known as Berry syndrome.

The clinical presentation of APW in infants is typically with symptoms of congestive heart failure due to a large left-to-right shunt through the defect. Symptoms can include tachypnea, poor eating, diaphoresis, dyspnea, and failure to thrive. Infants may also experience recurrent pneumonia. The defect dimensions determine the amount of shunting and pulmonary arterial pressures. Hemodynamically, a large APW is similar to a very large PDA, causing pulmonary overcirculation, dilation of the pulmonary artery, left atrium (LA), and left ventricle (LV), and leading to pulmonary hypertension. Physical examination findings may include a parasternal lift due to right ventricular (RV) overload, a loud single second heart sound indicating pulmonary hypertension, and increased peripheral pulses. A murmur, potentially similar to a PDA murmur, may be present, especially with smaller defects.

Echocardiography is generally the diagnostic imaging modality of choice for APW. It allows for the direct imaging of the communication and flow through it using color Doppler. Echocardiography can also demonstrate the presence of two separate arterial valves, helping to distinguish APW from common arterial trunk. Antenatal diagnosis is possible, though rare, often suspected with a dilated LA/LV. Chest X-ray may show cardiomegaly, prominent pulmonary vascular markings, and hyperinflation. ECG can be normal but may show left atrial enlargement or LV/RV hypertrophy. CT and MRI can be helpful for detailed anatomy, especially to rule out coexisting anomalies or when echocardiography is uncertain. Cardiac catheterization is not routinely required for diagnosis but might be indicated in older patients to assess pulmonary vascular resistance if late repair is considered.

Early surgical repair is indicated for APW, typically at presentation and preferably before age 3–6 months to prevent pulmonary vascular changes. Preoperative management may involve medical treatment for heart failure. Surgical repair usually involves median sternotomy and cardiopulmonary bypass. The typical technique involves division of the window with patch repair of both the aortic and pulmonary defects, taking care to identify and protect the coronary ostia. A transcatheter approach has been reported but is not the approach of choice.

Postoperative care for simple APW is usually uncomplicated. However, patients, especially those with late presentation, may have potential for postoperative pulmonary hypertension. Other potential residual lesions or complications include residual shunt, narrowing of the pulmonary artery or aorta, or coronary ostial stenosis.

Outcomes after surgical repair of APW are generally excellent, particularly when performed early in life. Operative mortality for isolated defects is low, often less than 2%. Outcome in complex cases depends on the associated defects. Long-term outcomes are also reported as excellent, with low rates of late complications. However, patients with complex APW, especially those with concomitant arch repair, have a higher risk of requiring reoperation, often for aortic obstruction. If left unrepaired, a large APW can lead to progressive pulmonary vascular disease, obstructive pulmonary hypertension (Eisenmenger syndrome), heart failure, and has a poor prognosis with significant mortality in infancy.

References

• Abdulla, Ra-id, Al-kubaisi, Maytham, Alsaleh, Leen, & Awad, Sawsan. (2016). Pediatric Electrocardiography.

• Dipchand, A. I., et al. (eds.). (2024). Manual of Cardiac Care in Children. Springer Nature Switzerland AG. https://doi.org/10.1007/978-3-031-70973-9 

• Morgan, Conall, & Dipchand, Anne I. (n.d.). Aortopulmonary Window. In A. I. Dipchand et al. (eds.), Manual of Cardiac Care in Children.

• Park, I. S., & Kim, S.-J. (2019). [Book title likely related to Echocardiography in Congenital Heart Disease],. © Springer Nature Singapore Pte Ltd.

• Park, I. S., & Goo, H. W. (2019). Patent Ductus Arteriosus Aortopulmonary Window. In I. S. Park & H. W. Goo, [Book title likely related to Echocardiography in Congenital Heart Disease],. © Springer Nature Singapore Pte Ltd.

• Rudolph, Abraham M. (2009). Congenital Diseases of the Heart: Clinical-Physiological Considerations (Third Edition). A John Wiley & Sons, Ltd., Publication. ISBN: 978-1-405-16245-6

• ScienceDirect. (2011). Aortopulmonary Window. Seminars in Thoracic and Cardiovascular Surgery: Pediatric Cardiac Surgery Annual, 14(1), 67-74. https://doi.org/10.1053/j.pcsu.2011.01.017.

• Echocardiography in Congenital Heart Disease Made Simple.

• Aortopulmonary window. In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Aortopulmonary_window&oldid=1193287110.

• Bin-Moallim, Mohammed, Hamadah, Hussam K, Alhabshan, F., Alghamdi, A.A., & Kabbani, M.S. (2020). Aortopulmonary window: Types, associated cardiovascular anomalies, and surgical outcome. Retrospective analysis of a single center experience. Heart Views, 32(2), 127–133. https://doi.org/10.37616/2212-5043.20.

AP windown from the apical view in 2D (outlined by the red arrow).