A young female presents with history of dyspnoea on exeion. On examination, she has wide, fixed split S2 with ejection systolic murmur (IIINI) in left second intercostal space. Her ECG shows left axis detion. The most probable diagnosis is ?

Ans. is 'c' i.e., Ostium primum atrial septal defect Wide fixed splitting of S2 in association with ejection systolic murmur suggests the diagnosis of Atrial septal defect. o Ideally with hyperophy of the right side of the hea, right axis detion should be present, but sometimes left axis detion is also seen in A.S.D. Explanation for the presence of left axis detion in A.S.D. o Atrial septal defects are of two types Ostium primum atrial septal defect Ostium secundum atrial septal defect o This division depends upon the development of interatrial septum and related structures. o Ostium secundum type atrial septal defect is the classical atrial septum defect. o Presence of interatrial septum is the only developmental anomaly in ostium secundum type and associated with right axis detion. In contrast the ostium primum defects are characterized by presence of ceain other developmental abnormalities, besides the interatrial septum. o Once such abnormality is the malformation or lack of development of the anterosuperior division of the left bundle branch. o Maldevelopment of antero superior division of the left bundle branch is responsible for abnormal left axis detion.