Ostium Membrane Opening

Ostium means a small orifice or opening, such as a body organ. And the words ostium primum means an opening in the lower portion of the membrane dividing the embryonic atria into right and left sides. It is also called foramen primum. An ostium primum atrial septal defect can be caused due to failure in fusing. This is the most common type of the atrial septal defect and is often associated with the trisomy 21.

While the heart is in the developing mode, there is a time when the atria start to communicate with one another by a small opening which is between the free edges of the septum primum and the atrioventricular cushions, called the Ostium primum also known as the interatrial foramen primum, below the free margin of the septum. One of the most common causes that lead to Ostium primum atrial septal defect is genetic.

The most common defect, which is the Ostium primum atrial septal defect, is located in the most anterior and inferior aspect of the atrial septum. This defect is the simplest form of atrioventricular canal or atrioventricular septal defect. The causes of this defect in children are still unknown. Research into the molecular genetic basis for atrioventricular canal and atrioventricular septal defects is still in process.

Except for an anterior and inferior space that is present in the Ostium primum, the septum primum is divided by the rudimentary atrium during the fetal development. During the fifth week of the gestation the ostium primum is sealed by the fusion of the superior and the inferior endocardial cushions. Incase this fails it leads to ostium primum atrial septal defect.

The endocardial cushion helps in the completion of two separate atrioventricular and the inlet interventricular septum. This is the only reason that Ostium primum atrial septal defect is so commonly associated with the malformations of all these structures. This defect may also exist in isolation but they quite commonly coexist with the cleft in the anterior leaflet of the mitral valve.

In the United States Ostium primum atrial septal defect are quite commonly associated with the trisomy 21, which is commonly called Down syndrome. The incidence of trisomy 21 is 1 per 800 live births. This defect has increased a lot in children who are born to older mothers. The risk for the children inherited this defect from their parents who have atrioventricular septal defect is about 9 to 14%.

The risk of those patients with Ostium primum atrial septal defect is about 40-50%. And is about 65% for all those patients who have some form of the atrioventricular septal defect. Children who have trisomy 21 are at a quite higher risk than the general population of developing pulmonary vascular obstructive disease, which happens at quite young age. Ostium Primum