Is it your understanding that the two conditions are related? I'm not in the medical field, so my question is one of curiosity. I believe the bypass is to correct a blocked artery, in this case the left anterior descending (LAD, also known as 'the widowmaker.'). The amyloidosis is, I would think, an unrelated condition where some of the heart's muscle proteins are amyloidized, which makes them less able to function as myocytes, and this results in vessel wall thickening and stiffening.
You will surely get some first-hand experience from some members seeing your post.