Florian LangEncyclopedia of Molecular Mechanisms of Disease10.1007/978-3-540-29676-8_131
© Springer-Verlag GmbH Berlin Heidelberg 2009
Aortopulmonary Septal Defects
Lucia K. Ma1, Patrick T. S. Ma2 and Alexander K. C. Leung3
Royal College of Surgeons, Dublin, Ireland
Heart Health Institute and Department of Cardiac Science, The University of Calgary, Calgary, AB, Canada
Department of Pediatrics, Alberta Children's Hospital, The University of Calgary, Calgary, AB, Canada
Aortopulmonary window; Aortopulmonary fenestration or fistula; Aortic septal defect; Partial persistent truncus arteriosus; APSD
Definition and Characteristics
Aortopulmonary septal defect (APSD) is a rare congenital cardiac abnormality defined as a communication between adjacent portions of the ascending aorta (AAo) and the pulmonary artery (PA), with the presence of separate semilunar valves. APSD may exist as an isolated lesion, the rest (47−77%) are found in conjunction with other congenital heart disease, including patent ductus arteriosus, ventricular septal defects (20%) tetralogy of Fallot (6%), right aortic arch (5–20%), transposition of the great arteries (10%), interrupted aortic arch (8%), coarctation of the aorta (13–20%) and coronary artery anomalies (23%) . APSD is subdivided into three subtypes. Type I occurs between the origin of the main PA and the posteromedial wall of AAo immediately above the sinus of Valsalva. Type II describes a communication between the AAo and the origin of the right PA. It involves the anomalous origin of the right PA from the aorta. Type III is a defect between the PA and the majority of the AAo together with a Type II defect; here the right PA arises from the posterior or posterolateral AAo, and is completely separate from the main PA trunk. Most APSD is large and the blood flow is from left to right after birth. The common presentation is that of early congestive heart failure (CHF), irreversible pulmonary hypertension (PH), acute decompensation from intercurrent infections and death. Only a minority of patients with uncorrected APSD reaches their teens or young adulthood. The patients with smaller APSD are underdeveloped, tachypnoeic and have a tendency toward recurrent respiratory infections. Physical signs include bounding arterial pulse with wide pulse pressure, cardiac enlargement with a prominent apical impulse. The murmur of APSD is loud and harsh, and can be holosystolic or early systolic. Alternatively it can be continuous in restrictive APSD which accounts for 20% of all APSD cases. The murmur is usually loudest in the third left intercostal space. Other murmurs include Graham Steell murmur resulting from a dilated pulmonary trunk, and an apical mild diastolic mitral murmur caused by increased flow. When the flow across the APSD shunt is reversed from the development of suprasystolic PH, patients would develop increasing generalized cyanosis, a loud pulmonic ejection murmur, a loud single second beat, the stigmata of the Eisenmenger complex, and the disappearance of the systolic murmur across the defect.
APSD is a rare defect consisting of about 0.1−0.6% of congenital heart disease. The male to female ratio is about 1.8:1 and no racial trend exists.
Molecular and Systemic Pathophysiology
The aberrant embryogenesis of APSD originates from the incomplete fusion and/or malalignment of the right and left conotruncal ridges which may cause defective and unequal partitioning of the aortopulmonary (AP) trunk (Type I) and a more posterior and dorsal aorta. The abnormally positioned aorta may then connect to the right sixth aortic arch, which is the precursor of the right PA. Hence, the right PA may connect to the main PA as well as having an orifice into the aorta (Type II), giving rise to the anomalous origin of the right PA from the AAo. The pathophysiology of APSD is closely related to the size of the defect, the direction of blood flow across the shunt and the development of pulmonary hypertension. Regardless of the size, APSD does not affect the fetus. After birth, the fall in pulmonary vascular resistance (PVR) causes progressive shunting of blood from the systemic to the pulmonary circuit across the APSD. This results in PH, CHF and the development of pulmonary vascular obstructive disease which eventually would progress to shunt reversal and the Eisenmenger complex. The above progression is also highly dependant on the nature of the other congenital heart lesions if present.
The diagnostic features of APSD are dependant on the size and direction of the shunt, the presence of PH and associated congenital abnormalities. Differential diagnosis includes coronary artery anomalies, large patent ductus arteriosus, truncus arteriosus, pulmonary arteriovenous fistula, ruptured sinus of Valsalva aneurysm, and ventricular septal defect. Echocardiogram is usually the method of choice for the diagnosis of APSD . It shows enlarged cardiac chambers and measures PA pressure; the APSD can best be delineated with color flow Doppler. Cardiac magnetic resonance angiography can accurately visualize and measure the size of the APSD. Cardiac catheterization performed before surgery can identify a shunt at the level of the PA and assess the extent of PH and related congenital abnormalities. Selective aortography and manipulation of the catheter from the main PA directly to the AAo confirm the diagnosis.
As most APSD are large, irreversible PH occurs early. Hence, surgical closure is ideally performed in the first few months of life . Currently, the procedure of choice involves transaortic closure of the APSD by direct suture (small defects) or by using a prosthetic patch (large defects) while providing cardiopulmonary bypass [4,5]. Stenosis of grafts or surgical sites of the APSD repair are the most common long term complications. Patients should also receive bacterial endocarditis prophylaxis for life.
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