A "secondary AV fistula" refers to a fistula created after a pre-existing graft or fistula has either outright failed or been determined to be suboptimal for continued dialysis. The creation of secondary fistulas represents an important way in which nephrologists might increase their overall percentage of patients dialyzing via AV fistula (see "Fistula First Campaign") rather than simply targeting incident CKD patients initiating dialysis.
From a terminology perspective, a "Type I secondary AV fistula" refers to when the outflow vein of a pre-existing AVF or AVG is able to be used as a target for a new "converted" AVF; the advantage of Type I AVFs are that they can often be used shortly after placement, not requiring lengthy maturation times and potentially avoiding the use of a transient dialysis catheter altogether. In contrast, a "Type II secondary AV fistula" refers to an entirely new AVF, which can occur either on the ipsilateral or contralateral side with reference to the failed fistula.
How well do secondary AVF perform? In one 2002 report by Ascher et al, 71 secondary fistulas demonstrated a 1-year and 2-year primary patency rate of 58% and 22%, respectively. These results are not suprisingly worse than the primary patency rates for primary AVFs (75% and 61%, respectively), but nonetheless demonstrate that in a few dialysis patients, the creation of a secondary AVF can give successful, long-term dialysis access. Hopefully, a better understanding of the process by which AV fistula fail could eventually lead to medications or surgical breakthroughs which might prolong the longevity of secondary access attempts.