Congenital Aortopulmonary Window- Types, Pathophysiology, Symptoms, Evaluation, Management

Introduction

Congenital aortopulmonary window is one of the rarest congenital heart diseases that occurs from the defect present between the proximal aorta and the main pulmonary artery. This abnormality could be isolated, but fifty percent of the individuals might be associated with cardiac abnormalities such as arch abnormalities, interrupted aortic arch, specifically coarctation of the aorta, Atrial Septal Defect (ASD), and Tetralogy of Fallot. To prevent irreversible pulmonary vascular disease, once the aortopulmonary window is diagnosed, surgical closure or catheter-delivered devices should be performed as soon as possible. Following the repair of the simple aortopulmonary windows, in the current era, the early mortality rate is low. It will also depend on the presence of associated lesions, especially interrupted aortic arch.

What Is an Aortopulmonary Window?

Aortopulmonary window is a cardiac abnormality that results from abnormal communication between the proximal aorta and the main pulmonary artery when two normally separated aortic and pulmonary valves are present. It is a relatively rare cardiac lesion when compared to other cardiac malformations.

What Are the Types and Clinical Features of Aortopulmonary Windows?

Aortopulmonary windows can be classified into proximal, distal, and total defects. The most common are the proximal defects located in the proximal aorta above the sinus of Valsalva. Distal types are seen in the upper portion of the ascending before the aortic branches. The total defects are large and involve most ascending aorta between the Valsalva and aortic branches. The clinical feature of aortopulmonary windows is that most individuals have the manifestations of a large left-to-shunt right. It might be asymptomatic in individuals with small defects, and symptoms are present in individuals with large defects, such as congestive heart failure and pulmonary hypertension in the first weeks of life. In the first months of life, severe pulmonary vascular hypertension can occur.

What Is the Pathophysiology of Aortopulmonary Windows?

During embryonic life, at nine weeks, an aortopulmonary septum forms, which will spiral and divide the truncus arteriosus into two great vessels, the pulmonary artery and the aorta. A deficiency in the aortopulmonary septum leads to aortopulmonary windows, and these defects can vary in size and shape. It is termed type I when the defect is away from the aortic valve. The defect is termed type II when it is proximal, closure to the aortic valve. The defect is termed type III, which involves the whole length of the aortopulmonary septum. When there is increased pulmonary blood flow, these defects tend to be larger with the onset of early pulmonary obstructive vascular disease if left untreated. The physiology of the aortopulmonary window will resemble a large Patent Ductus Arteriosus (PDA) or Ventricular Septal Defect (VSD) based on the size of the defect, the ratio of systemic and pulmonary vascular resistance and the degree of shunting.

What Are the Symptoms of an Aortopulmonary Window?

There are no symptoms noticed if the defect is small. Large defects can cause symptoms such as heart failure, delayed growth, irritability, poor eating and lack of weight gain, rapid heartbeat, respiratory infections, and rapid breathing. In most cases, surgery is successful to correct the defect.

How Is the Aortopulmonary Window Evaluated?

A diagnostic evaluation is done when the infant presents extremis or due to respiratory distress. There will be increased pulmonary vascular markings with mild to moderate cardiomegaly when viewed through chest X-ray. The absence of the aortic knuckle and the prominence of the main pulmonary segment can explain the other subtle findings on the X-ray. The electrocardiogram is considered non-specific and may show deep Q waves in lateral precordial leads due to increased pulmonary blood flow.

The diagnostic tool of the aortopulmonary window is an echocardiogram, which can identify the associated anomalies. A lack of wall or fallout between the aorta and pulmonary artery can be detected by 2D-electrocardiography, which can be best visualized in subcostal and short-axis parasternal views. The aortopulmonary window will have two well-formed semilunar valves. The left ventricle and left atrium might be enlarged due to volume overload to the pulmonary artery.

There can be an appreciation of echocardiographic features of elevated pulmonary vascular resistance in the late presentation of the aortopulmonary window. To assess for pulmonary vascular reactivity, cardiac catheterization is a diagnostic tool for the late presentation of the aortopulmonary window. Both in the pulmonary artery and aorta, cardiac catheterization would reveal equal systemic pressures.

How Is an Aortopulmonary Window Managed?

Cardiac surgery is the definitive management in the aortopulmonary window typically performed in the neonatal period. Congestive heart failure can be managed medically, which is an option if the patient’s condition is conducive to performing corrective surgery. Earlier surgeries can prevent irreversible changes in the pulmonary vasculature. In isolated defects, surgical techniques are quite simple, involving division and separation of the great vessels with patch closure of the defect. Median sternotomy and cardiopulmonary bypass are the surgical approaches, and their outcomes are excellent. Concomitantly, the surgeon also repairs the associated defects. To address the issues such as re-coarctation, reoperations might be necessary.

What Is the Differential Diagnosis of the Aortopulmonary Window?

An aortopulmonary window will resemble truncus arteriosus, a large vascular defect, and a large patent ductus arteriosus, as it has a similar presentation of a diastolic flow reversal. This can be identified and differentiated between various defects with the help of two-dimensional electrocardiography. Due to diastolic runoff, large pulse pressures are present in the aortic pressure estimation. An angiogram will identify the defect between the aorta and pulmonary artery. To identify suitable surgical candidates, pulmonary vaso-reactivity testing should occur.

Conclusion

Aortopulmonary window is one of the rarest congenital heart diseases that occurs from the defect between the proximal aorta and the main pulmonary artery. Surgical closure or catheter-delivered device is recommended in all patients to manage the aortopulmonary window. It should be performed as soon as possible once diagnosed to prevent irreversible pulmonary vascular disease.