78 and heart attack history probably not a good candidate for the operation. I had my op at 64 and actually waited too long and ended up with nerve damage. 71 now and doing well except for bouts of numbness.
Good luck & God Bless You
My cousin had both knees replaced in his mid-70’s. One knee replacement worked very good, other not so good. Although I am in exceptionally good shape for my age, I agree with you, it is best to avoid serious optional surgery in late 70’s..