Atrial septal defect

Electrocardiogram from a patient with a large atrial septal defect (3:1 left-to-right shunt). There is a right ventricular conduction delay with right axis deviation due to right ventricular hypertrophy. (qR complexes are sometimes seen in leads V1 and V2 with right-sided chamber enlargement). The tall P waves in V2 and V3 are due to right atrial enlargement. In comparison, mitral stenosis is associated with right ventricular hypertrophy plus left (not right) atrial enlargement.