The 4+2 programs exist only in institutions that have both a general
surgery residency and a vacular surgery fellowship. The 4+2 allows you
to skip your chief year of your general surgery residency and instead
start your vascular fellowship. It is really up to the discretion of
the program if they allow this to happen. You could contact ACGME as
well to see if they will tell you if a program has been approved for a
4+2. If you are interested in this option I would contact the vascular
surgery departments of the programs you like have offer this as an
option.