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KEY POINTS
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Key Points

  • Atrioventricular (AV) canal defect is the most common form of congenital heart disease detected prenatally and usually involves both a lower atrial and an upper ventricular septal defect, together with a common AV valve orifice.

  • In 70% of cases there will be additional cardiac malformations, and in the majority of isolated cases additional chromosomal abnormality will be diagnosed, most commonly trisomy 21.

  • Prenatal diagnosis of complete AV canal defect should be straightforward, by failure to visualize the normal crux on a four-chamber cardiac view.

  • Management of pregnancy includes detailed echocardiographic and general fetal anatomic evaluation, amniocentesis, and planned delivery with complete pediatric cardiology backup.

  • Overall prognosis is variable as prenatally diagnosed AV canal defects represent a heterogenous group.

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CONDITION
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Atrioventricular (AV) canal defect is also known as an AV septal defect, common AV canal, endocardial cushion defect, ostium primum atrial septal defect, or persistent ostium atrioventriculare commune. Complete AV canal defect consists of an unrestrictive atrial septal defect, an unrestrictive ventricular septal defect, and a single common AV valve. It occurs because of failure of development of the endocardial cushion during embryogenesis and persistence of the primitive single AV canal beyond 6 weeks of gestation. Although the AV canal defect may involve a wide spectrum of abnormalities of the atrial and ventricular septa and the AV valves, the complete form with associated AV valve regurgitation is the one that most commonly presents during the neonatal period (Chin et al., 1982).

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AV canal defects can be partial or complete. With a partial AV canal defect, there are two separate AV orifices, with communication between two atria or between the left ventricle and the right atrium. While the right AV valve is usually normal, the left valve usually has three leaflets (Becker and Anderson, 1981). With a complete AV canal defect, there is a defect in the inferior portion of the atrial septum and the superior portion of the ventricular septum, together with a single AV valve orifice, which usually has five valve leaflets. The anterior and posterior valve leaflets are inserted on the anterior and posterior surfaces of the ventricular septum, respectively; the degree of bridging of the anterior leaflet across the ventricular septum determines the type of defect (Rastelli et al., 1966). For type A complete AV canal defects, the anterior leaflet does not bridge the ventricular septum and is attached on both sides of the septum by chordae tendineae (Silverman et al., 1986). For type B complete AV canal defects, the anterior leaflet somewhat bridges the ventricular septum and is attached to the right ventricle by an anomalous papillary muscle. For type C complete AV canal defects, the anterior leaflet is not attached to the septum, and completely bridges it, being attached at either side by papillary muscles. Type A is commonly seen in trisomy 21, and type C is ...

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