I want to write about these two defects because they are very similar to each other. I also want to write about the embryological development of the heart.
This is all very important to understanding the development of heart defects
The heart begins as a bulbous muscular organ that within a few weeks begins to form a fibrous structure that will eventually develop into the future four chambers of the heart and also form the four valves.
The fibrous skeleton of the heart develops last. It eventually creates a cross like structure that ends in the so called “crux of the heart” or the middle of the heart. The fibrous skeleton begins at at the top and bottom of the heart as well as the lateral sides, It grows inward until it all meets at center, thus forming the “crux” of the heart.
If all four inward growing fibrous structures of the heart fail to meet at the center, then numerous heart defeats develop.
It will result in a VSD, ASD, or malformation of the mitral and tricuspid valves, or all of the above, As well, it may involve a malformations of the aortic and pulmonic valves.
This fibrous skeleton will form a fibro muscular portion that blends into a fibro muscular portion that eventually becomes the muscular potion that makes up most of the heart.
The pulmonic RVOT ( right ventricular outflow tract) portion is primarily fibrous, and forms an elongated right ventricular outflow tract. otherwise known as the “conus” The left ventricular outfow tract is primarily fibro muscular, and the aortic structure is derived from there.
When the crux fails to form at the center, you can end up with an ASD, VSD and a possible malformation of the mitral and or tricuspid valve. Viola…a big hole in the center of the heart as well as as multiple valvular defects.
In other words, an AV Canal (or endocardial cushion defect) ends up as a big hole in the heart, and is similar to a Tetralogy of Fallot in that in the latter, the pulmonic valve and or the RVOT and conus are also compromised (in addition to possibly mitral and tricuspid valves,
Please read further for more information.
Ken Heiden RDCS