<s>[INST] context: Wide fixed splitting of S2 in association with ejection systolic murmur suggests the diagnosis of Atrial septal defect.
Ideally, with hypertrophy of the right side of the heart, right axis deviation should be present, but sometimes left axis deviation is also seen in A.S.D.


The explanation for the presence of left axis deviation in A.S.D


Atrial septal defects are of two types


Ostium primum atrial septal defect
Ostium secundum atrial septal defect


This division depends upon the development of interatrial septum and related structures.
Ostiutn secundum type atrial septal defect is the classical atrial septum defect.
Presence of interatrial septum is the only developmental anomaly in ostium secundum type and associated with right axis deviation.
In contrast, the ostium primum defects are characterized by the presence of certain other developmental abnormalities, besides the interatrial septum.
Once such abnormality is the malformation or lack of development of the anterosuperior division of the left bundle branch.
Maldevelopment of antero superior division of the left bundle branch is responsible for abnormal left axis deviation. [/INST] question: A young female presents with a history of dyspnoea on exertion. On examination, she has wide, fixed split S2 with ejection systolic murmur (III/VI) in left second intercostal space. Her ECG shows left axis deviation. The most probable diagnosis is – | options: A: Total anomalous pulmonary venous drainge B: Tricuspid atresia C: Ostium primum atrial septal defect D: Ventricular septal defect with pulmonary arterial hypertension | answer: C </s>