Aortopulmonary window

What is Aortopulmonary Window?

Aortopulmonary window or aortopulmonary septal defect (APSD) is a congenital heart disease, which represents the presence of a communication between the adjacent parts of the ascending aorta and the pulmonary trunk.

Embryology

Aortopulmonary septal defect is caused by violation of division of the conotruncus into the aorta and pulmonary trunk. Under the influence of various etiologies, the aortopulmonary window is formed due to the incomplete fusion of the aorticopulmonary septum.

Anatomy

APW can be located differently: proximally, distally, or may occupy intermediate position. The dimensions of the defects vary widely: from little 2 mm communications to wide defects, significantly affecting hemodynamics. 

A feature that distinguishes the aortic pulmonary window from truncus arteriosus is the preservation of two normal semilunar valves. Aortopulmonary septal defects are often associated with other congenital heart abnormalities: interrupted aortic arch, coarctation of the aorta, etc.

Classification

1. Type I - aortopulmonary window is located above the level of the Valsalva sinuses.
2. Type II - the location of the defect in the distal part of the septum, capturing the orifice of the right pulmonary artery.
3. Type III – large defect, both pulmonary arteries originate from the posterior surface of the aorta.
4. Type IV - intermediate.

Hemodynamics

APSD refers to CHD with increased pulmonary perfusion. The severity of hemodynamic disturbances is determined by the size of the window and the ratio of general and peripheral vascular resistance. The volume of shunted blood from the aorta to the pulmonary artery is low, if the size of the window is small, and the pressure in the pulmonary artery may be normal. If the size of the window is large, pulmonary hypertension is noted at an early age.

The left ventricle and the left atrium experience a volume overload during the diastole due to the large blood volume returning from the lungs. The right ventricle is not subjected to volume overload. However, due to the blood ejection into high-pressure vessels, a moderate pressure overload develops. With the development of pulmonary hypertension, the overload on the left ventricle decreases, while on the right ventricle it persists or even increases.

A reflex spasm of the pulmonary vessels occurs as a response to hypervolemia. It’s a compensatory mechanism that protects against overflow and reduces predisposition to pulmonary edema. However, a prolonged increase in the smooth muscles tone of the precapillary vessels activates the next stage of compensatory reactions aimed at the structural fixation of the lumen of the pulmonary vessels - sclerosis. Irreversible changes in the pulmonary vessels with reversal of the shunt gradually develop to adolescence.

Workup

• Echocardiography, CT. Visualization of the APSD and concomitant congenital heart defects.
• ECG. The symptoms are variable, reflecting the degree of the overload on the left or right heart. Signs of overload of the left heart appear first. In presence of pulmonary hypertension – deviation of the electrical heart axis to the right, hypertrophy of the right ventricle signs. 
• Chest radiography. The heart is moderately dilated, the pulmonary artery bulges, the edges of the left atrium and the left ventricle protrude. The arc of the ascending aorta is not protruded, edematous lungs, strengthened pulmonary pattern.
• Cardiac catheterization. Allows setting the degree of pulmonary hypertension, the magnitude and direction of blood shunt.

Clinical presentation

Clinical symptoms are characteristic for defects with a left-right blood shunt (dyspnea, tachycardia, lack of appetite, poor weight gain). Recurrent respiratory diseases, congestive crackles, hypotrophy occur with the development of heart failure.

Cyanosis may occur briefly in the first weeks of life, while crying. It is associated with the development of venous blood shunt from the pulmonary artery into the aorta. Cyanosis in older age indicates the development of pulmonary hypertension.

The earliest and characteristic symptom is dyspnea, with abdominal and chest breathing, involving auxiliary muscles. Pulse pressure is increased due to leakage of arterial blood into the lungs.

Auscultatory findings depend on the size of the APW and the volume of blood shunt. It should be remembered that this defect is often combined with other CHDs, which can distort the auscultatory picture.

• Loud systolic murmur.
• Continuous murmur (if the defect is small) in the ІІ – ІІІ intercostal space on the left sternal border.
• Short murmur with strengthened second heart sound above the pulmonary artery - a sign of the development of pulmonary hypertension.
• If the resistance of the pulmonary vessels increases, murmurs may be absent, or the diastolic Graham Still's murmur (pulmonary valve insufficiency) may be determined.

Treatment

Surgical treatment is indicated in the early terms, within the first year of life, considering the rapid development of pulmonary hypertension and other complications. If the defect is relatively small, it is possible to perform ligation of the APW. In other cases, the closure of the defect using a patch is performed.

After development of pulmonary hypertension, it is impossible to perform a radical operation, so a two-stage surgery is performed: 1 - narrowing of the pulmonary artery; 2 - radical surgery.