Background: Stenosis is the main cause of arteriovenous fistula (AVF) failure. It is unclear, however, if surveillance for stenosis enhances AVF function and longevity and if there is an ideal time for intervention.
Methods: In a 5-year randomized, controlled, open trial we compared blood flow surveillance and pre-emptive repair of subclinical stenoses (one or both of angioplasty and open surgery) with standard monitoring and intervention based upon clinical criteria alone to determine if the former prolonged the longevity of mature forearm AVFs. Surveillance with blood pump flow (Qb) monitoring during dialysis sessions and quarterly shunt blood flow (Qa) or recirculation measurements identified 79 AVFs with angiographically proven, significant (>50%) stenosis. The AVFs were randomized to either a control group (intervention done in response to a decline in the delivered dialysis dose or thrombosis; n = 36) or to a pre-emptive treatment group (n = 43). To evaluate a possible relationship between outcome and haemodynamic status of the access, AVFs were divided into functional and failing subgroups, according to Qa values higher or lower than 350 ml/min or the absence or presence of recirculation.
Results: A Kaplan-Meier analysis showed that pre-emptive treatment reduced failure rate (P = 0.003) and the Cox hazards model identified treatment (P = 0.009) and higher baseline Qa (P = 0.001) as the only variables associated with favourable outcome. Primary patency rates were higher in treatment than in control AVFs in both functional (P = 0.021) and failing subgroups (P = 0.005). They were also higher in functional than in failing AVFs in both control (P<0.001) and treatment groups (P = 0.023). Access survival was significantly higher in pre-emptively treated than in control AVFs (P = 0.050), a higher post-intervention Qa being the only variable associated with improved access longevity (P = 0.044). Secondary patency rates were similar in pre-emptively treated and control AVFs in both functional (P = 0.059) and failing subgroups (P = 0.394). They were also similar in functional and failing AVFs in controls (P = 0.082), but were higher in pre-emptively treated functional AVFs than in pre-emptively treated failing AVFs (P = 0.033) or in the entire control group (P = 0.019).
Conclusions: We provide evidence that active blood flow surveillance and pre-emptive repair of subclinical stenosis reduce the thrombosis rate and prolong the functional life of mature forearm AVFs. We also show that Qa is a crucial indicator of access patency and a Qa >350 ml/min portends a superior outcome with pre-emptive action in AVFs.