Background
Aortopulmonary window (APW) is a defect between the great vessels that results from failure of the conotruncal ridges to fuse. It is separate from truncus arteriosus in that it is associated with essentially normal aortic and pulmonary valves. The defect usually begins just above the sinuses of Valsalva and then extends a variable distance distally into the arch. [1]
For patient education resources, see the Heart Health Center, Aortic Aneurysm of the Abdomen and Thorax (Chest) and Congestive Heart Failure.
History of the Procedure
Aortopulmonary window was first described in the 19th century, and the first repair was performed in 1952 by Robert E. Gross, MD, at Boston Children's Hospital. [2] Subsequent development of cardiopulmonary bypass techniques simplified the repair. Currently, an incision directly into the aortopulmonary window or the aorta is used. Most lesions are repaired by direct patch repair of the defect.
Problem
Aortopulmonary window produces a large and usually unrestricted left-to-right shunt that worsens as pulmonary vascular resistance falls during the newborn period. Congestive heart failure and low cardiac output can rapidly follow. These patients are particularly susceptible to Eisenmenger syndrome at an early age because of combined systolic and diastolic run-off into the pulmonary circulation. Aortopulmonary window is frequently associated with other cardiac defects that affect outcome and complicate repair.
Epidemiology
Aortopulmonary window may occur as an isolated lesion or as part of a larger complex of lesions and represents approximately 0.2% of all congenital cardiac lesions. Two of the largest series reported, from Boston Children's Hospital and Northwestern University, show that an active center can expect about one case per year. [3]
Etiology
Aortopulmonary window represents a failure of the conotruncus to differentiate into the aorta and pulmonary artery. No genetic associations or environmental risk factors are known. The two competing embryologic theories are (1) that aortopulmonary window is part of a spectrum of conotruncal abnormalities, which includes truncus arteriosus at one end of the spectrum, and (2) that aortopulmonary window is unrelated to truncus arteriosus because the lesions associated with each defect are so dissimilar.
Pathophysiology
The hemodynamic abnormalities are similar to those seen with a large, unrestrictive ventricular septal defect (VSD) or patent ductus arteriosus. Aortopulmonary window is characterized by a large left-to-right shunt that becomes progressively worse as pulmonary vascular resistance falls during the newborn period. Volume overload and pulmonary overcirculation lead to progressive left ventricular dysfunction and congestive heart failure.
The common association of distal arch obstruction or interrupted aortic arch with aortopulmonary window acts as an obstruction to systemic flow and further increases the left-to-right shunt. [4] Perfusion to the lower body therefore depends on flow through the ductus arteriosus. Closure of the ductus results in severe hypoperfusion of the lower body, pulmonary overcirculation, and impending congestive heart failure.
Presentation
The presentation depends on the size of the lesion and the systemic and pulmonary vascular resistances. As discussed above, the presence of obstructive lesions in the distal aorta increases the severity of symptoms.
Rarely, the lesions are small and restrictive, in which case the symptoms may be mild. More commonly, however, the defects are nonrestrictive, and the patient presents with congestive heart failure. Symptoms may include tachypnea, tachycardia, irritability, poor feeding, and lack of weight gain. If the shunt is sufficiently large, infants may present in severe heart failure with low cardiac output and severe acidosis.
Physical examination reveals an active precordium with a second heart sound that is accentuated and not split. A systolic murmur and widened pulse pressure are characteristic.
Patients who present after infancy have a high prevalence of pulmonary vascular hypertension and a rapid progression to Eisenmenger syndrome within the first years of life. These patients may present with milder symptoms because of improvement in the left-to-right shunt and decreased pulmonary overcirculation. Any infant older than approximately 6 months should be considered at high risk for pulmonary hypertension, and cardiac catheterization should be considered.
Indications
The presence of an aortopulmonary window (APW) is the only indication necessary for repair. Spontaneous closure is not known to occur. Delay in repair risks development of pulmonary vascular hypertension and Eisenmenger syndrome. Therefore, repair should be undertaken at the time of diagnosis and after initial stabilization.
Relevant Anatomy
Aortopulmonary window (APW) represents a spectrum defined by the distal extension of the defect. Large defects produce a confluence of the aorta and main pulmonary artery. In these patients, the branch pulmonary arteries are often abnormally positioned. In particular, the right pulmonary artery may originate from the aorta and further distal extension is associated with interrupted aortic arch (usually type A) and patent ductus arteriosus, a constellation of findings known as Berry syndrome. [5]
More than half of patients with aortopulmonary window have additional associated lesions. They range from patent ductus arteriosus and atrial septal defect (ASD) to interrupted aortic arch, tetralogy of Fallot, and total anomalous pulmonary venous drainage. [6]
The coronary arteries can arise abnormally. One or both of the coronary arteries may arise from the area of the confluence or from the pulmonary artery. [7]
Contraindications
The primary contraindications to surgery in patients with aortopulmonary window (APW) are similar to those in a patient with a large ventricular septal defect (VSD). Ideally, patients should undergo repair before the onset of pulmonary vascular hypertension. In patients older than 6 months, cardiac catheterization should be considered. If significant pulmonary hypertension is present, reversibility should be demonstrated by the administration of vasodilators. The presence of irreversible pulmonary hypertension is a contraindication to repair.
