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Congenital Heart Defects - AVSD
 1. Central defect in the atrio-ventricular septum. Typically one defect. The portion above the atrio-ventricular valves is often referred to as the "primum ASD" and the portion below the valves as the VSD. 
Horizonal Cross-section through a Normal Heart
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 2. There is a single, complex atrio-ventricular valve spanning the area of the defect rather than the two separate valves guarding two separate atrio-ventricular openings.  3. In addition to rebuilding the central septum of the heart with a patch, the single atrio-ventricular orifice and its valve are separated into right and left components and valve reconstruction involves attaching these valves to the patch and typically closing the cleft of the left-sided atrio-ventricular valve to reduce regurgitation or leakage. |
Atrioventricular septal defects (AVSD) are a relatively common family of congenital heart defects.
The primary defect is the failure of formation of the part of the heart that arises from an embryonic structure called the endocardial cushions. The endocardial cushions are responsible for separating the central parts of the heart near the tricuspid and mitral valves (AV valves), which separate the atria from the ventricles.
The structures that develop from the endocardial cushions include the lower part of the atrial septum (wall that divides the right atrium from the left atrium) and the ventricular septum (wall that divides the right ventricle from the left ventricle) just below the tricuspid and mitral valves.
The endocardial cushions also complete the separation of the mitral and tricuspid valves by dividing the single valve between the embryonic atria and ventricles. An atrioventricular septal defect may involve failure of formation of any or all of these structures.
