Aortopulmonary septal defect
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Aortopulmonary septal defect (APSD) is a congenital anomaly where there is an abnormal communication between the proximal aorta and the pulmonary trunk in the presence of separate aortic and pulmonary valves.
APSD should not be confused with the radiographic term aortopulmonary window, which refers to a mediastinal space on chest radiographs and CT scans.
Aortopulmonary septal defects occur in <1% of all cardiac malformations 1,2.
The clinical presentation of aortopulmonary septal defects is dependent on the size of the defect and on the associated lesions. The presentation is usually similar to that of other patients with left-to-right shunts. Severe cases present as congestive heart failure. Cardiac examination reveals an enlarged heart, and like patients with patent ductus arteriosus (PDA), the pulses are bounding. A systolic murmur can be heard along the left sternal border. However, unlike patients with a PDA, a diastolic component to the murmur is rare. Patients with associated arch abnormalities frequently present with shock coinciding with the closing of the ductus arteriosus.
Aortopulmonary septal defect results when there is a failure of fusion of the two opposing conotruncal ridges that are responsible for separating the truncus arteriosus into the aorta and pulmonary artery. The defect occurs between the ascending aorta and the main pulmonary artery and may be found just above the semilunar valves or between the more distal ascending aorta and main pulmonary artery.
It has similar hemodynamic features to a patent ductus arteriosus, or, even more so, to a common truncus arteriosus, the anatomical difference from the latter being the presence of two separate semilunar (aortic and pulmonary) valves 1,2.
Several classifications of APSD have been proposed at the time of writing (July 2016), this below-mentioned classification is most widely accepted in literature.
This classification separates APSD into four types 3:
type I: proximal APSD located just above the sinus of Valsalva, a few millimeters above the semilunar valve
type II: distal APSD located in the uppermost portion of the ascending aorta
type III: total defect involving the entire aortopulmonary septum or ascending aorta
type IV: intermediate defect
50-70% of all patients with APSD are associated with other cardiac malformations 3,4,5:
right ventricular outflow tract (RVOT) anomalies
left ventricular outflow tract obstruction
Allows direct visualization of the defect. The defect can be best visualized from different views by echocardiographic study, including parasternal short and long-axis views, high parasternal short-axis view, and subcostal coronal view. At Doppler echocardiography, abnormal continuous forward flow in the pulmonary arteries indicates the presence of an aortopulmonary communication 2.
CT angiography allows direct visualization of the defect and associated anomalous anatomy.
Allows direct visualization of the anomalous anatomy. SSFP cine sequences can offer an additional functional assessment.
Treatment and prognosis
Early surgical or device closure is indicated as soon as the diagnosis is established to prevent congestive heart failure and pulmonary hypertension. Associated cardiovascular defects should also be repaired. The outcome of patients with this anomaly is excellent if correction is performed before complications of the disease arise 2.