Atrial Septal Defect, Ostium Primum

Ostium primum ASD is a variant of AV canal defect. Classified as an ASD, it is actually an endocardial cushion defect.

Less common than secundum ASDs, this defect comprises 0.5-1% of all congenital heart defects, and 15-20% of ASDs.

Approximately 50% of pts with primum ASD are female.

Ostium primum is most commonly associated with the genetic defect trisomy 21 (Down syndrome). It is also associated with Holt-Oram and Noonan syndrome.

Periop mortality rate: 1.5-6%, lower mortality if repair is done before onset of pulm Htn.

Late in clinical course of unrepaired, clinically significant ASDs; CHF is common with a L-to-R shunt.

Increased risk of atrial dysrhythmias, heart block, and air embolus with surgical repair.

Significant risk of mortality if Eisenmenger syndrome (eventual reversal of the shunt into a cyanotic R-to-L shunt) has occurred. Surgical repair is often not recommended at this point.

AV valves, which are usually abnormal

Abnormal conduction axis

CHF and Eisenmenger syndrome

Failure of inferior atrial septum to close at the level of the tricuspid and mitral valves.

Symptoms present earlier, are more severe than in secundum ASD, and include dyspnea, fatigue, atrial arrhythmias, recurrent respiratory infections, and failure to thrive.

L-to-R shunt increases pulmonary blood flow and right-sided volume overload.

Progression of clinical course: CHF (more common than in secundum pts) and shunt reversal (R-to-L flow across ASD).

Frequently associated with mitral regurgitation with a cleft in the anterior mitral leaflet (can cause left-sided volume overload) and/or tricuspid regurgitation.

Diagnosis by ECHO; characteristic appearance: Absence of the lower atrial septum.

Cardiac catheterization may be required to assess PVR and pulm Htn in large shunts.

Failure of septum primum to fuse with endocardial cushion to close ostium primum