Tackling the main culprit, stenosis in the arteriovenous anastomosis and outflow veins, with balloon angioplasty before it is “too late” can boost maturation rates in slow-to-mature arteriovenous (AV) fistulas. Robert Jones, consultant interventional radiologist at the Queen Elizabeth Hospital Birmingham, UK, set out his endovascular treatment strategy of balloon-assisted maturation at the recently held Vascular Access Society of the Americas 2021 Spring Virtual Conference (VASA). He also deliberates on whether drug-coated balloons (DCB) might have a role to play in the immature fistula.
AV fistulas can have high rates of protracted maturation with up to 60% being reported in the literature as ‘slow to mature’. Best efforts at “precisely and quantitatively” defining these fistulas are covered by the statement that they “do not see increase in flow and diameter to adequately support dialysis,” explained Jones.
Relatively narrow window of time for optimising interventional success
“When and how do we best pick up a slow-to-mature fistula with a view to intervention?” asked Jones who went on to frame the “relatively narrow window” for maturation interventions with the statement: “If a fistula has not matured by four to six weeks, it is unlikely to.”
This time window charts the latest Kidney Disease Outcomes Quality Initiative (KDOQI) guideline that considers it reasonable for operators to evaluate for postoperative complications within two weeks [of access creation] and an appropriate member of the vascular access team to evaluate for AV fistula maturation by four to six weeks after.
Jones also touched on an important-to-recognise later presentation scenario that could prompt endovascular intervention—when maturation failure is identified later on by unsuccessful attempts at fistula cannulation.
Up to 50% of fistulas need help to mature
Postoperative AV access maturation rates can vary; according to Jones, but approximately half of fistulas will need at least one intervention before they are functional.
Stenosis is the main offender in the slow-to-mature fistula and most commonly occurs in the in the juxta-anastomotic region. Accessory side-branch veins can also be responsible for slow maturation in 30–50% of cases and can occur in isolation or in association with stenosis, he reported.
Again, referring to the KDOQI guideline that states good quality studies comparing surgical and endovascular techniques for post-operative maturation are either lacking, or have conflicting results, Jones highlighted that an individualised patient approach with a first-line endovascular approach is customary in this nearly fact-free zone.
“Despite there being little high-quality data that directly compares maturation rates achieved using endovascular interventions against those achieved with surgery, balloon assisted maturation takes centrestage, and I often consider using a brachial artery access using a micro-puncture kit to get a diagnostic fistulogram as a roadmap in the first instance at the time of intervention,” he said.
The road to balloon-assisted maturation
Jones recommended an endovascular plan to treat maturation failure that begins with a physical exam to locate the type and level of the lesion. This is followed by an ultrasound exam to confirm these findings; exclude any thrombosis; and assess the depth of the fistula. “Ultrasound can also identify accessory veins,” clarified Jones. Finally, a fistulogram and intervention complete the pathway. “This [fistulogram] allows us to create a definitive roadmap and anatomical assessment to map out where the stenosis and accessory veins are, and the relevant lesion is then treated,” he said.
Jones urged VASA attendees to consider the whole access circuit with the reminder that stenoses in the arterial circuit can occur quite proximally and so could need additional cross-sectional imaging in a small number of cases, especially when a peripheral lesion cannot be identified using standard assessment.
“I tend to start with an 0.018” balloon platform, then move to a high-pressure balloon if necessary. If unsuccessful, I move to a cutting balloon,” Jones stated.
With regard to the management of branch veins, Jones suggested adopting a ‘watch and wait’ strategy to see how the fistula fares after balloon maturation. “Or, you could compress the branch vein under ultrasound to determine its significance. If on compression of the branch vein there is improved palpable thrill over the fistula itself, the branch vein should ideally be occluded in the same episode. If it is superficial, consider suture ligation (or coiling), but if it is located in the deep vasculature, use coils [to obliterate],” he said, illustrating with case examples that repeat interventions are often required to keep the circuit patent.
“There is evidence supporting repeated sequential angioplasty produces a good result, and this is often required to achieve continuity in outflow from the artery to the vein and a fairly uniform vessel that will go on to mature.”
Complications can occur, and include haematoma, extravasation from rupture, and thrombosis. These are most commonly seen in forearm fistulas according to the literature, cautioned Jones.
Primary patency outcomes of endovascular maturation are reported to be slightly inferior to those achieved with surgery, as determined by Jan Tordoir and colleagues in a systematic review published in the European Journal of Vascular and Endovascular Surgery (EJVES) in 2018. The review also reported clinical success rates with endovascular maturation procedures (angioplasty and vein obliteration) in the range of 43–97%.
Jones pressed home the importance of secondary patency in fistula intervention and the benefit that the minimally invasive balloon-assisted maturation strategy conveys with rates reported to be 68– 96% in the systematic review. He also referenced data from Timmy Lee and colleagues published in the Journal of the American Society of Nephrology in 2019 on the positive association between the number of interventions in the slow-to-mature fistula and likelihood of functional primary patency loss and frequency of post-maturation interventions.
“In summary, balloon-assisted maturation can increase the number of functional fistulas: get in there early with a three-step management approach involving the physical exam, ultrasound and then, finally, intervention. Remember to consider the whole access circuit and you are looking to treat stenosis and accessory veins,” Jones stated. Looking to the future, Jones told Renal Interventions that more data is required in this area, and that it would be particularly interesting to determine the value of drug-coated balloons (DCB) in treating immature fistulas. “To date, studies have examined the application of DCB in treating dysfunctional fistulas already in use, with only a few cases reported of this application in the immature fistula,” he said.