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The ostium primum atrial septal defect is a defect in the atrial septum at the level of the tricuspid and mitral valves. This is sometimes known as an endocardial cushion defect because it often involves the endocardial cushion, which is the portion of the heart where the atrial septum meets the ventricular septum and the mitral valve meets the tricuspid valve.
The secundum atrial septal defect usually arises from an enlarged foramen ovale, inadequate growth of the septum secundum, or excessive absorption of the septum primum. About 10 to 20% of individuals with ostium secundum ASDs also have mitral valve prolapse .
Foramen secundum atrial septal defects are the most common atrial septal defects. This defect can arise as a result of defects of the septum primum and the septum secundum. For the septum primum, the problem can arise as a result of excess resorption of the septum during the process of apoptosis in order to form the foramen secundum.
Now, we also have the septum secundum which grows downward just to the right of the septum primum, and covers the ostium secundum like a curtain, leaving a small opening called the foramen ovale, and essentially creating a makeshift valve that allows blood to go from right atrium to left atrium, but not the other way.
The gap below it is known as the ostium primum (from Latin 'first opening'), and becomes increasingly small. The septum primum eventually fuses with the endocardial cushion, closing the ostium primum off completely. Meanwhile, perforations appear in the superior part of the septum primum, forming the ostium secundum (from Latin 'second opening').
Failure of the septum primum to fuse with the endocardial cushion can lead to an ostium primum atrial septal defect. [1] This is the second most common type of atrial septal defect [2] and is commonly seen in Down syndrome. Typically, this defect will cause a shunt to occur from the left atrium to the right atrium.
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Septal defects that may occur with Lutembacher's syndrome include: Ostium primum atrial septal defect or ostium secundum which is more prevalent. [1] Lutembacher's syndrome affects females more often than males. [1] It can affect children or adults; the person can either be born with the disorder or develop it later in life.