Depending on the type of bypass, subclavian stenosis can compromise a bypass graft. The left Internal Mammary (LIMA) is a branch of the subclavian artery and if LIMA is used for bypass, subclavian stenosis can cause problem with blood supply to the heart. Depending on the stenosis this can be treated with a percutaneous catheter based procedure/ stent, and may not require surgery.
So this is something that happened after the bypass? Did the bypass cause this? If it was there during the bypass would it not have been caught by the doctor doing the bypass....I am not sure what mammary was used for the bypass...I will have to ask my mother about that one....It just seems to me that the blockage was probably there when the bypass was done unless it got clogged again within a year and a half....