The atrioventricular canal, or AV canal, is the structure that forms the center of the heart. During normal fetal development, the endocardial cushions grow together to form walls that divide the left and right sides of the heart from each other and form the right and left valves that divide the atria from the ventricles.
An AV canal defect, or endocardial cushion defect, is a condition that arises because the endocardial cushions fail to divide the left and right sides of the heart and form the atrioventricular valves in the normal way.
This results in a group of related abnormalities that includes an atrial septal defect, or ASD, a ventricular septal defect, or VSD, and malformed AV valves.
In an AV canal defect, the walls, or septa, between the right and left sides of the heart are not completely formed, which allows blood to flow from the left chambers of the heart into the right chambers. The AV valves, which include the tricuspid and mitral valves, also form abnormally, often resulting in a single, or common, AV valve which directs blood into both the right and left ventricles.
An AV canal defect can be repaired surgically. The procedure includes closing the atrial and ventricular septal defects with one or two patches.
The single AV valve is divided into two valves to reconstruct the right-sided, or tricuspid, and left-sided, or mitral valve. The leaflets of the left AV valve, or mitral valve, often need to be partially closed with stitches to reduce leakage, or regurgitation.
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