Ostium secundum ASD
Complete RBBB, RBBB pattern or rsR' pattern in lead C1.
Normal axis or right axis deviation due to right ventricular diastolic overload.
Right atrial abnormality (may not be observed in children).
Prolongation of the PR interval: first degree atrioventricular block (less frequent than ostium primum ASD).
Crochetage : notched R wave in inferior limb leads (may disappear after closure of the defect).
If the defect is very large, severe atrial dilatation results in atrial flutter of fibrillation in adults.
In adult patients with ASD, closure of the defect does not decrease the incidence of atrial fibrillation.
Ostium primum ASD
rsR' pattern in lead C1 (V1).
Left axis deviation (due to absence of the left anterior fascicle).
Left axis deviation persists even after closure of the defect.
Determination of QRS axis is very important in the differential diagnosis of ostium secundum
and ostium primum ASD.
Right axis deviation is not observed in ostium primum ASD.
Left atrial abnormality.
Complete or incomplete RBBB.
Prolongation of the PR interval (first degree atrioventricular block).