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).