Fetal atrioventricular septal defect
Atrio-ventricular septal defect (AVSD) is characterized by an incomplete division of the atria and ventricles, resulting in a single common valve between the atria and ventricles. This condition is commonly seen in children with Down syndrome. Typically, there are 2 big categories of AV canal (AVSD): partial AV canal and complete AV canal. Complete AV canal can further be subdivided regarding balanced and unbalanced. There may also be associated anomalies, as more complex anatomical variants (such as those with heterotaxy, total abnormal pulmonary venous connection/return, interruption of inferior vena cava with with azygos continuation, etc.). Unbalanced AV canal may present complex variations, with: outflow tract obstruction (pulmonary or systemic), the inflow(s) committed to one ventricle, the hypoplasia of one of the ventricular chambers, etc.).
Case of balanced atrio-ventricular septal defect
Fetal case of complete atrioventricular septal defect. The atrial and ventricular components with common atrioventricular orifice. There is balanced ventricles with no left or right-sided atrioventricular valvular regurgitation. No evidence of LVOT obstruction or antenatal suspicion of coarctation. Both atrioventricular valves are at the same level (in normal anatomy: tricuspid valve implanted lower than the mitral valve).
Cases by Dr Wadi Mawad - pediatric cardiologist at the Montreal Children's Hospital: Balanced, unbalanced, single-ventricle AVSD with TAPVR:
Common AV valve opening equally over 2 well developed ventricules