Primum Atrial Septal Defect

Primum Type ASD

In this case, the ostium primum is patent because the septum primum does not fuse with the endocardial cushions. Recall that the cushions are responsible in forming a portion of septum primum, thus obliterating ostium primum. You may wish to review atrial partitioning at this time.

Figure

• FO = Foramen ovale
• IEC = Inferior endocardial cushion
• SEC = Superior endocardial cushion
• O1 = ostium primum