Primum atrial septal defect

What it means

An ostium primum atrial septal defect is located in the most anterior and inferior aspect of the atrial septum. The ostium primum refers to an anterior and inferior opening (ostium) within the septum primum, which divides the rudimentary atrium during fetal development. The ostium primum is normally sealed by fusion of the superior and inferior endocardial cushions around 5 weeks' gestation. Ostium primum defects result from a failure of the fusion of the embryologic endocardial cushion and septum primum.

With this type of ASD, communication persists when the septum primum fails to fuse with the endocardial cushions, thus leaving an opening between both atria near the atrial floor, being a mid/late event in atrial septation. Due to the association with endocardial cushion abnormalities, this defect may be associated with either atrioventricular valve anomalies, such as mitral valve cleft, or a complete atrioventricular septal defect.

Rare diseases that can present with this2

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Atrial septal defect, primum type · ostium primum ASD · Ostium primum atrial septal defect · Primum atrioventricular canal defect · Septum primum defect