In addition to demonstrating comparable performance in terms of long-term patency, durability and associated complications, early-cannulation arteriovenous (AV) grafts may hold some advantages when contrasted with standard expanded polytetrafluoroethylene (ePTFE) graft products. That is according to transplant and vascular access surgeon Nicholas Inston (Queen Elizabeth Hospital Birmingham, Birmingham, UK), who discussed the potential held by early-cannulation grafts, and the appropriate scenarios in which to use them, at the Vascular Access Society of the Americas 2021 Spring Virtual Conference (VASA, 21–22 May, online).
“Early-cannulation grafts appear to have no disadvantages compared to standard ePTFE grafts—and they may hold some advantages,” he said. “These advantages are likely to be mainly seen early on in avoiding central venous catheters [CVCs] in late-presenting patients, and when used for salvage. Ultimately, however, the use of early-cannulation grafts, as well as the choice of which graft to use, comes down to availability and personal preference.”
Inston opened his presentation at VASA 2021 by discussing when he personally chooses to use an AV graft—noting that the most common situations include when the patient in question has exhausted all autologous options or has unfavourable veins, as well as occasions when there is simply no time to use their native tubes. He added that one of the key benefits early-cannulation grafts hold over autologous AV fistulas is the lack of any maturation period associated with the former, as grafts can potentially be ready and functioning within 72 hours of implantation.
Regarding practical reasons for using and selecting an early-cannulation graft, Inston stated that one of the most important questions is: can you get hold of the graft? “If it is on the shelf, we can use it,” he said. “Personally, I tend to be in a position where I can get Acuseal [Gore] and Flixene [Getinge]—but this will vary in different countries. Affordability will also apply to this, although affordability of grafts when applied against using a CVC is very insignificant.”
Inston highlighted the importance of handling from a physician’s point of view, stating that ‘kinkability’, tunnelling systems, graft deployment systems (GDS), and wall thickness, should all be taken into consideration, and went on to stress the significance of timing in the deployment of early-cannulation grafts, adding that there is evidence to suggest using them “in an aggressive fashion” could decrease the need for CVCs in dialysis patients.
In terms of the performance seen in early-cannulation grafts, Inston also asserted, through a 2019 Journal of Vascular Access (JVA) systematic review authored by himself and Julien Al Shakarchi (Department of Renal Surgery, University Hospitals Birmingham, Birmingham, UK), that “no major differences” were seen in primary and secondary 12-month patency between several products—including Vectra (Thoratec) and AVflo (Nicast), which both displayed “adequate long-term patencies”, as well as the aforementioned Acuseal and Flixene grafts. Regarding complications, the same review showed “very little difference” between any of the early-cannulation grafts for infection rates and occurrences of access thrombosis.
Inston also touched on the durability of these grafts, stating that “these grafts are designed for early cannulation, but their structure implies they would be more suitable for prolonged dialysis access”. He went on to add that multiple studies have shown no real benefits to using standard ePTFE grafts compared to early-cannulation grafts in terms of patency or failure rates at 18 months. Inston concluded his presentation by warning of the complications that can arise from repeated graft cannulation—including material breakdown, and outflow stenosis leading to pseudoaneurysm—but did also cite a benchtop study in which ePTFE grafts were associated with “significant injury” from needling, while the early-cannulation grafts used in the study, Acuseal and Flixene, were not.
The long-term future of early-cannulation grafts
Following VASA 2021, Shawn Gage, a member of the VASA board of directors, and founder of medical device company InnAVasc Medical (Durham, USA)—who was also a senior vascular physician’s assistant (PA) and functioned as a junior vascular surgeon for nearly 15 years within the Division of Vascular Surgery at Duke University—spoke to Renal Interventions in an effort to expand on some of the current challenges facing AV grafts.
Gage highlighted the fact that high flow in veins and resulting neointimal hyperplasia, and infection risks, seen following implantation of a graft are both complications associated with ePTFE and early-cannulation options alike that are not currently addressed by any graft products on the market today. He also alluded to several approaches that may provide hope on these fronts, including human biologic graft materials that have been investigated as a solution to infections, and the fact that everything from altering flow dynamics to the use of drug-coated balloons have been looked at as a means for managing venous outflow pathology.
However, while many of these potential solutions are still relatively early stage right now, an area that may see advancements in the more immediate future is also one that Inston highlighted in his VASA 2021 presentation: durability. While Gage concurred with Inston’s claims that there appears to be little difference between the two main graft types—early-cannulation and standard ePTFE—in terms of functional durability and patency outcomes, he added that it is still “very important to have improved durability over what we currently have”. “Any time you put one [a graft or fistula] in, you want to maintain it for as long as you can, and, if you can make a graft survive for five years, that is a big deal,” Gage claimed. “Unfortunately, current graft lifespans are somewhere between one and two years—it is not very long.”
In addition, the increased uptake in at-home dialysis in recent years, which holds several benefits compared to in-centre dialysis but also involves grafts being needled on a more frequent basis, has only compounded the need to ensure long-term durability, according to Gage. “If you are starting to undergo at-home dialysis five or six days per week, rather than three, you are going to significantly accelerate the degradation process and shorten the lifespan of the graft,” he added. “That is really where durability in this new home-haemodialysis era is going to be extremely important.”
Gage also noted that the definition of durability is important to consider as well, and may go beyond simply “how long the graft stays open and working”. He said: “Now, we really need to drill down into failure modes, and how the graft is failing—is it failing because of clotting, and if it is clotting, is it failing because of an outflow vein narrowing? That is a common complication that neither one of these grafts [standard ePTFE or early-cannulation] solves. Or, are we talking about failure from issues of material degradation, such as pseudoaneurysms, and bleeding and haematomas?”
Gage concluded that, without a randomised clinical study, it will be hard to characterise these different failure modes in early-cannulation grafts, adding that “it is absolutely fair to say that a lot more research is needed to try to figure out if it is even worth using an early-cannulation graft—we think it is, but this bears further investigation”. Gage also stated that, in addition to working with Inston closely in the future to spin out this idea of what durability means in early-cannulation grafts, another key area he would like the two to focus on further down the line is developing a guidance document, or a set of guidelines, around how to best utilise these grafts, and in which scenarios.
“There are times where patients do not have another option, and then the risks associated with early access become worth it for the potential benefits—but, in patients that do have other options, perhaps it makes sense to wait for one or two weeks before accessing,” he added. “This allows for postoperative pain and inflammation to resolve while still being aggressive with early catheter removal.”