AORTOPULMONARY WINDOW

The aortopulmonary window (APW) is a rare congenital heart defect characterized by an abnormal communication between the ascending aorta and the main pulmonary artery, resulting from a defect in the embryologic separation of the common arterial trunk. This condition leads to a left-to-right shunt, allowing oxygenated blood to pass from the aorta to the pulmonary artery, causing pulmonary overcirculation and progressive pulmonary hypertension if left untreated.

During fetal development, the separation between the aorta and pulmonary artery occurs through the formation of the conotruncal septum, derived from neural crest cells. A failure in its fusion can result in defects of varying severity, including aortopulmonary window and other anomalies of the conotruncal region, such as persistent truncus arteriosus. The classification of aortopulmonary window is based on its position and size:

Type I (Proximal): The defect is located in the most proximal portion, between the ascending aorta and the main pulmonary artery.
Type II (Distal): The defect is positioned distally, near the bifurcation of the pulmonary artery.
Type III (Total): A large communication involving a wide portion of the ascending aorta and the pulmonary artery.

Pathophysiology

An aortopulmonary window allows oxygenated blood to pass from the aorta into the pulmonary artery, creating a high-pressure left-to-right shunt. The main pathophysiological consequences include:

Pulmonary overcirculation: Increased blood flow to the pulmonary circuit, leading to elevated venous return to the left atrium and dilation of the left heart chambers.
Increased pulmonary artery pressure: Excessive blood flow into the pulmonary artery leads to progressive pulmonary hypertension**.
Progression to Eisenmenger syndrome: If left untreated, the rise in pulmonary vascular resistance leads to shunt reversal (right-to-left), resulting in systemic cyanosis.

Clinical Presentation

Symptoms depend on the defect size and the magnitude of the shunt. Newborns with a large aortopulmonary window quickly develop signs of congestive heart failure. Key symptoms include: Tachypnea, exertional dyspnea, continuous or systolic murmur heard in the left parasternal region, bounding peripheral pulses due to wide pulse pressure, failure to thrive in neonates with severe pulmonary overcirculation.
In advanced cases, cyanosis occurs due to shunt reversal.

Diagnosis

Diagnosis is based on clinical and instrumental investigations:

Echocardiography with Doppler: First-line imaging technique to confirm the defect and quantify the shunt.
Cardiac catheterization: Used for direct measurement of pulmonary artery pressure and assessment of pulmonary hypertension reversibility.
Cardiac magnetic resonance (CMR): Helpful in complex cases for detailed anatomical characterization.
Chest X-ray: May reveal **cardiomegaly** and **pulmonary overcirculation**.

Treatment

Surgical repair is the definitive treatment for aortopulmonary window and should be performed as early as possible to prevent irreversible pulmonary vascular damage.

Direct defect closure using a synthetic patch or autologous pericardium.
Ligation and separation of the aorta and pulmonary artery in more extensive cases.

In cases of severe pulmonary hypertension, palliative pulmonary artery banding may be necessary before definitive closure. If treated early, aortopulmonary window has an excellent prognosis. However, if left uncorrected, it can progress to irreversible Eisenmenger syndrome, making surgical correction no longer feasible.

Conclusion

Aortopulmonary window is a rare but potentially fatal congenital heart defect if not promptly treated. Early diagnosis and surgical intervention are essential to ensure a favorable outcome and prevent pulmonary hypertension and heart failure.

References

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Brown JW, Ruzmetov M, Okada Y, Vijay P, Turrentine MW. (2004). *Surgical repair of aortopulmonary window: a 40-year experience.* The Annals of Thoracic Surgery, 77(2), 506-510.
Sadiq M, Latif F, Rehman AU. (2003). *Aortopulmonary window: 15 years' experience at a tertiary care centre.* Journal of Ayub Medical College Abbottabad, 15(4), 12-15.
Saxena A, Kothari SS, Juneja R, et al. (1993). *Aortopulmonary window: clinical profile and surgical results—experience with 21 cases.* International Journal of Cardiology, 42(3), 265-270.