Aortopulmonary (AP) window is a rare congenital anomaly, accounting for 0.2 to 0.5 percent of all congenital heart defects.¹ It consists of a communication between the aorta and the pulmonary artery or its branches. Although closely related to AP window, pulmonary artery origin from the ascending aorta (also erroneously termed “hemitruncus”) is classified as a separate defect.

AP window was first described by Elliotson in 1830 in an autopsy study.² In 1948, Robert Gross successfully ligated an AP window in a patient undergoing a thoracotomy for closure of a patent ductus arteriosus (PDA).³ In 1957, Cooley and associates described the first successful repair of AP window using cardiopulmonary bypass.⁴

The pathophysiology of AP window is similar to that of a ventricular septal defect, PDA, or truncus arteriosus consisting of a left-to-right shunt. The amount of left-to-right shunting is related to the size of the defect and the pulmonary vascular resistance. Patients with small defects can be completely asymptomatic. With large defects, and as the pulmonary vascular resistance decreases in the first weeks of life, symptoms of congestive heart failure develop rapidly, and irreversible pulmonary vascular disease can occur as early as during the first 12 months of life. If untreated, 40 percent of patients will die of intractable heart failure during the first year of life, and survivors will succumb to the sequelae of congestive heart failure and severe irreversible pulmonary vascular disease during childhood (Fig. 67-1).⁵

This defect has also been called AP septal defect; however, in terms of the structure of the postnatal heart and beyond the initial few months of gestation, there is no such thing as an AP septum. Almost as soon as the aortic and pulmonary pathways become separate entities within the developing heart, each of the intrapericardial arterial trunks develops its own discrete arterial wall. AP window is the failure of formation of the separate adjacent walls of the intrapericardial arterial trunks, with persistence of the AP foramen that certainly does exist during embryological development.⁶ This defect can be differentiated from common arterial trunk by the presence of two separate arterial valves arising from separate subarterial ventricular outflow tracts.

AP window was classified by Mori et al.⁷ into three types (Fig. 67-2):

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  Type I: The most common type; involves proximal defects located between the semilunar valves and the pulmonary bifurcation.

  
  
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  Type II: Distal defects located in the uppermost portion of the ascending aorta, with the posterior border of the defect formed by the pulmonary bifurcation.

  
  
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  Type III: The defect is posterior in the aorta, creating a communication with the right pulmonary artery.

The Congenital Heart Surgery Nomenclature and Database project uses a classification system that is similar to the one just described.⁸ A Type 1 proximal defect involves an AP window located just above the sinus of Valsalva, a few millimeters above the semilunar valves, with a superior rim but little inferior rim separating the AP window from the semilunar valves. Type 2 distal defect is located in the uppermost portion of the ascending aorta, with a well-formed inferior rim but little superior rim. Type 3 total defect involves the majority of the ascending aorta, with little superior and inferior rims. The intermediate type is a defect similar to the Type 3 but with well-defined superior and inferior rims. Interrupted aortic arch (IAA) is one of the most common associated cardiovascular lesions seen in patients with an AP window; the ventricular septum is usually intact and type A interruption is most commonly encountered.

AP window is also associated with VACTERL syndrome, which involves vertebral anal, tracheoesophageal renal and limb anomalies. Other associated lesions include tetralogy of Fallot, ventricular and atrioventricular septal defects, anomalous origin of the either coronary arteries from the pulmonary artery, transposition of the great arteries, and double aortic arch.

The clinical presentation is related to the magnitude of the left-to-right shunt. In early life patients present with signs and symptoms of congestive heart failure, including failure to thrive and frequent respiratory tract infections. The smaller size defects are associated with minimal or no symptoms. On cardiac ausculation a systolic murmur is usually heard. Cyanosis is a late finding, presenting with the development of severe pulmonary vascular obstructive disease. When associated malformations are present, the clinical presentation can change to reflect the combined hemodynamic features, with IAA usually presenting with metabolic acidosis and poor perfusion after PDA closure, making the clinical diagnosis of AP window more challenging.