From the RSTC GUIDELINES FOR RECREATIONAL SCUBA DIVERS PHYSICAL EXAMINATION:
Severe Risks
Venous emboli,commonly produced during decompression, may cross major intracardiac right-to-left shunts and enter the cerebral or spinal cord circulations causing neurological decompression illness.
Now, I'm no physician, but it seems that if you can show conclusively that the ASD is completely closed, then this may not be a factor. A call to Diver's Alert Network would be wise for further advice on this point.
Of course, other factors should be considered and a review of the complete Physician's Guidelines would be prudent.