Atrial Septal Defects - A Review

Atrial septal defects are of 4 types

1. Ostium secundum defect

• Most common type
• Seen in the middle of the interatrial septum at fossa ovalis

2. Ostium primum defect

• Defect seen adjacent to the central fibrous body
• Associated with cleft anterior mitral valve leaflet - can result in mitral regurgitation

3. Sinus venosus defect

• Abnormal communication seen between right atrium and junction of either superior (more common) or inferior vena cava
• May be associated with partial anomalous pulmonary venous drainage

4. Coronary sinus defect - is rare.

Diagnosis

1. ECG

• Right axis deviation and right bundle branch block in ostium secundum ASD. rSR’ seen in precordial leads
• Left axis deviation in ostium primum ASD or in ostium secundum ASD with mitral valve defect

2. Echocardiography

• ASD best visualized in subcostal view on transthoracic echo
• Highly sensitive for ostium primum defects
• Least sensitive for sinus venosus defect
• 2D and Color doppler
• Right atrium and ventricle are dilated
• Paradoxical septal motion is seen
• Left to right shunt is seen
• Bubble contrast echo is useful

Further investigation is rarely required. Transesophageal echo may be useful if not visualized well on TTE, especially if defects are < 10mm wide.