Atrial septal defect ostium primum anatomy

Ostium primum defects usually occur due to the failure in fusion of the septum primum with the endocardial cushion.

• It occurs from the failure of fusion of the septum primum with the endocardial cushion.
• The endocardial cushion, is the portion of the heart where the atrial septum meets the ventricular septum and the mitral valve meets the tricuspid valve.
• It involves the inferior portion of the septum.
• Due to this, these defects commonly occurs in association with other cardiac anomalies such as atrioventricular valves (the mitral valve and the tricuspid valve).
• The abnormalities of the atrioventricular valves include the cleft mitral valve, and the single atrioventricular valve (a single large, deformed valve that flows into both the right ventricle and the left ventricle).
• These are usually large sized defects when compared to the secundum defects.
• Endocardial cushion defects are the most common congenital heart defect that is associated with Down’s syndrome.

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