I am a 35 year old female. A few months ago an ECG showed that i have a bifascicular block (right bundle branch block with left posterior fascicle block). An atrial septal defect was suspected. One has now been found but it is small, clinically insignificant, and doesn t need to be closed. I am at a loss as to why I have this block. I have researched it extensively and have learnt that the particulr combination of block I have is very rare and very serious with a 70% chance of proceeding to complete heart block. I would appreciate your view on the matter. Apart from this recently discovered block I am in excellent health. Thank you.

Summarized question: What causes bifascicular block with an atrial septal defect?