The primary findings of this study were as follows: 1) The protocol yielded an overall thrombosis rate of 0.068/pt-yr with a procedure rate of 1.43/pt-yr. There was no difference in the thrombosis rate among the three sub-protocols. 2) The target rate of abtAVF was comparable with the protocol rate of the ang sub-protocol group. 3) The abtAVF group had significantly higher thrombosis and AVF loss rates, and a lower thrombosis-free primary patency compared with the n-abtAVF group. However, there were no significant differences in the secondary patency. 4) The n-abtAVF(periodic) group had the lowest thrombosis rate. 5) The n-abtAVF (od) group had a higher thrombosis rate, but a lower procedure rate compared with the n-abtAVF(periodic) group.
To avoid AVF thrombosis, a follow-up protocol with a protocol rate greater than or equal to the target rate of the follow-up group should be selected to prevent AVF thrombosis. In the present study, the target rate of the abtAVF group and the protocol rate of the ang sub-protocol were similar, while the thrombosis rate of the abtAVF group was significantly higher than that of the ang sub-protocol. We believe this may have been attributed to a lower procedure rate in the abtAVF group. Among the 33 abtAVFs, only 14 were followed under the ang sub-protocol, while the others were followed under the opd sub-protocol. Under the opd sub-protocol, the interval from stenosis detection to angioplasty was approximately 2 weeks. Such a deferred correction of stenosis may lead to AVF thrombosis. Therefore, we believe that if the abtAVFs were followed under the ang sub-protocol, at the expense of an increased procedure rate, their thrombosis rates could have been reduced. That is, the appropriate IPF for the abtAVFs may be 103.5 days rather than 115.6 days.
Regarding the n-abtAVF group, if the goal of follow-up was to pursue a low thrombosis rate, the periodic sub-protocols (opd or ang) were considered appropriate because they yielded the lowest thrombosis rate. If patients wanted to undergo a procedure only when there was AVF dysfunction and the interventionist considered that their AVFs were not difficult to salvage once thrombosis occurred, the od sub-protocol was a reasonable option, because the goal of follow-up is to maintain an acceptably higher thrombosis rate compared with other target follow-up groups by following a sub-protocol with a lower procedure rate.
According to Quencer et al. (6), VA site thrombosis accounts for 65–85% of access loss. Therefore, lowering the thrombosis rate would reduce the risk of VA site loss. However, in the present study, the thrombosis rate of the abtAVF group was significantly higher than that of the n-abtAVF group, although their AVF loss rates were similar. This may have been attributed to recent innovations in endovascular techniques, which allowed us to handle challenging situations during the salvage procedure. Such innovations include endovascular bypass techniques for AVFs without recanalizable outflow veins, and the venotomy and manual propulsion technique for removal of massive thrombi (7–10). Therefore, some VA sites may have been abandoned in the past but are now salvageable.
An important question is whether pursuing a low AVF thrombosis rate should be considered a patient-important outcome measure for AVF monitoring and surveillance. According to dissenters, surveillance leads to an increased procedure rate without confidence that it extends the life of the AVF as measured by secondary patency rates (11, 12). However, other studies reported that preemptive treatment of subclinical stenosis reduced the AVF loss rate and prolonged the functional life of AVFs (13).
From the perspectives of the patient and the interventionist, we believe that pursuing a low thrombosis rate should be considered a patient-important outcome measure. In addition to the pain at balloon dilatation and thrombus propulsion during the salvage procedure, there may be severe complications, such as venotomy wound infection and bleeding, hypovolemic shock, and pulmonary embolism. Additionally, compared with simply dilating stenoses, interventionists generally require more time and use more tools to salvage thrombotic VA sites. To salvage engorged and tortuous AVFs, especially those with more than one pseudoaneurysm, the procedure may take 2–3 h, and the risk of salvage failure is relatively high.
It may be controversial to recommend pursuing a low thrombosis rate for every VA site. We believe that pursuing a low thrombosis rate should be mandatory for the following populations of VA sites:
-
Salvage-challenging AVFs: These AVFs have the following features: a) a thrombotic, enlarged, and tortuous AVF with one or multiple pseudoaneurysms; b) a thrombotic AVF with heavy and extensive calcifications, especially around the perianastomotic area; and c) a thrombotic AVF without recanalizable outflow veins. Once a salvage-challenging AVF develops thrombosis, the odds of achieving successful salvage become very low. That is, for salvage-challenging AVFs, avoiding thrombosis prolongs their usable lives.
-
Patients who have nearly exhausted all available VA sites for hemodialysis.
In the present study, the overall thrombosis-free primary patency at 1 year was 94.1%. This was comparable with the results of AVFs followed by clinical monitoring combined with Qa surveillance (87–97%) (13–15). The 1-year thrombosis-free primary patency was lowest in the abtAVF group (78.3%). However, this was superior to results of AVFs followed up exclusively by clinical monitoring (61–62%) (13, 14). The AVF loss rate of the abrupt thrombosis group (0.027/pt-yr) was comparable with rates reported previously for AVFs followed by clinical monitoring combined with the Qa surveillance (0.024–0.066/pt-yr) (13, 16).
The present study had the following limitations. 1) The study was designed and conducted retrospectively. 2) There may have been recall bias in identifying abtAVFs. 3) The follow-up protocol and sub-protocols were not verified for follow-up of AV grafts. 4) The efficacy of the ang sub-protocol for follow-up of the abtAVF group requires verification with further study.