Complete Atrioventricular Canal (aka AV canal, common atrioventricular canal, atrioventricular septal defect, endocardial cushion defect)
A complete atrioventricular canal (CAVC) describes a constellation of defects which comprise abnormalities in the structures that are derived from the endocardial cushions. In a complete AV canal, both the right and left atrium connect to the ventricles via a common (single) AV valve instead of two discrete (tricuspid and mitral) AV valves. There are deficiencies in both the atrial (primum ASD) and ventricular (inlet VSD) septum. CAVC results in a significant interatrial and interventricular systemic-to-pulmonary shunting, leading to right ventricular pressure and volume overload and pulmonary hypertension. CAVC accounts for approximately ~3% of cardiac malformations. Both sexes are equally affected and there is a significant association with Down syndrome/Trisomy 21. Patients often become symptomatic in infancy due to congestive heart failure and failure to thrive. Pharmacologic therapy (digoxin, diuretics, vasodilators) play a role as a bridge toward surgery which is usually performed between the 3-6 months of life.
Depending on the morphology of the superior leaflet of the common atrioventricular valve, 3 types of CAVC have been delineated (type A, B and C, according to Rastelli's classification). The anatomic subgroups (Rastelli's type A, B and C) can be classified on the basis of the chordal insertions and morphology of the superior bridging leaflet of the common atrioventricular valve.
Type A: The superior bridging leaflet demonstrates chordal attachments to the crest of the interventricular septum (~50-70%)
Type B: The superior bridging leaflet attaches past the crest of the ventricular septum to an anomalous papillary muscle on the right side of the ventricular septum (~3%, rare)
Type C: The superior bridging leaflet demonstrates no attachments to the ventricular septum and is referred to as a free floating leaflet (~30%).
Image above used with permission from Texas Children's Hospital and courtesy of the division of cardiothoracic surgery
Lai W, Mertens L, Cohen M, Geva T. Echocardiography in pediatric and congenital heart disease from fetus to adult. 2009. 230-248.