DCB evidence stokes demand for more research

The second day of the 2023 meeting of ASDIN played host to a packed afternoon session on new technologies for interventional nephrology. Amidst this came a presentation from Daniel Patel (Volusia Flagler Vascular Center, Daytona Beach, USA) on drug-coated balloon (DCB) use in arteriovenous fistula (AVF) stenosis.

Patel launched into a discussion of plain balloon and DCB angioplasty, noting that the former has a primary patency rate of only 50% after six months according to a 2019 systematic meta-analysis led by Ian Jun Yan Wee (National University of Singapore, Singapore). “Is there a better way to do what we do?” he asked. “Is there a physiological way rather than a mechanical way that we can get a better outcome here?”

Moving to focus on paclitaxel, he raised results from a study into its use with the Lutonix (BD) balloon published in 2018 in the Clinical Journal of the American Society of Nephrology (CJASN). This study, by Scott Trerotola (Perelman School of Medicine of the University of Pennsylvania, Philadelphia, Pennsylvania) et al, found that DCB angioplasty was equivalent in terms of safety with plain-balloon, but that it “did not meet the primary effectiveness end point at 180 days compared with conventional angioplasty”. It demonstrated no “no difference in access circuit patency” as well as “no lesion-specific benefit of DCB”.

Patel said “the story is not completely over for Lutonix”, drawing attention to the ABISS trial underway in France that has suggested “some improvement in Lutonix outcomes”, but that there was not yet meaningful data from this study to analyse. He also posed the question of whether paclitaxel-based DCBs could demonstrate better primary patency rates with higher doses. Initial concerns regarding risk of mortality with Pacl -

“Downright scary” distal radial artery cannulation illuminated

Rajeev Narayan (San Antonio Health Center, San Antonio, USA) has presented at ASDIN 2023 to give his tips and tricks on distal radial artery cannulation. “There are many things that are exciting in the field of nephrology,” said moderator of the session Anil Agarwal (Veterans Administration Central California Health Care System, Fresno, USA), introducing Narayan and his talk’s topic, “but some of them are downright scary”. Narayan aimed to shed some useful light on the procedure.

“BASICALLY,” NARAYAN SAID, “THE MORE YOU do something, the better you get at it—so this talk is mainly for those who do not do [distal radial artery cannulation] as much.” Beginning with indications, Narayan said that the procedure was appropriate for haemodynamic monitoring, as well as access for maturation of percutaneous arteriovenous fistula and dialysis access procedures.

He then moved on to assessing the safety of the procedure for a patient, something for which he emphasised the value of the complete superficial palmar arch (SPA) itaxel doses have not been demonstrated multiple DCB dialysis access studies, Patel argued. More recent studies, he said, are beginning to examine the effects on animal models of higher doses of the drug in angioplasty than have previously been tried, up to 6μg compared to the 3–4μg of previous studies. These include a 2021 investigation by Ole Gemeinhardt (Humboldt-Universität zu Berlin, Berlin, Germany) et al and the deep palmar arch (DPA), making reference to a review by Marek Brzezinski (VA Medical Center, San Francisco, USA) et al from 2009. Using a modified Allen test (MAT), he advised clinicians to use the following instructions: “Make a fist for 30 seconds with occlusion of both radial and ulnar arteries. Open the hand and release ulnar artery.” Then, he said, if colour returns in 3–12 seconds, the patient will likely be able to tolerate radial artery occlusion. If the patient can demonstrate a complete palmar arch with ultrasound or Doppler, he added, this may be “better at predicting ischaemia to the hand with radial artery occlusion”. If the ulnar artery is not patent, he stressed, “I would avoid distal radial artery cannulation”.

The IN.PACT Arteriovenous (AV) Access IDE study, published in The New England Journal of Medicine (NEJM) and carried out by Robert A Lookstein (Ichan School of Medicine at Mount Sinai, New York City, New York) et al, did also find that DCB was superior to plain-balloon angioplasty “for the treatment of stenotic lesions in dysfunctional haemodialysis arteriovenous fistulas during the six months after the procedure”. Its three-year data has also shown the benefits of “reduced interventions” while also demonstrating “improved patency” and “potential for cost savings” in comparison to treatment with plain balloon angioplasty. Sirolimus was also addressed in the course of Patel’s talk. Describing it as “effective in preventing arterial re-stenosis”, he cited the MATILDA trial published in the European Journal of Vascular and Endovascular Surgery (ESVS) and the ISABELLA trial cited in the Journal of Vascular Access (JVA). These prospective studies signalled efficacy of Sirolimus in treating dialysis access stenosis, Patel suggested, though he noted further studies are ongoing.

Finally, Patel asked: “are we there yet?” There remain many unanswered questions on DCBs, he argued, including particularly the advantages of a higher dose of paclitaxel. He also questioned whether “cutting balloon vessel prep” and employing larger-diameter balloons may be effective. He said data from the IN.PACT AV study were “compelling”, while DCBs may be“ideal for poor stent areas” like cannulation zones and vessel junctions.

Narayan urged his audience to remember “if nothing else” to cannulate above the level of the radial styloid. “We were all taught to cannulate at a 45 degree angle, but I do not really do that nowadays,” he added. “I come in at a much steeper angle nowadays and level off—I find that that is easier.” Another trick Narayan recommended was ulnar artery compression, which entailed using ultrasound “to localise and compress the ulnar artery, sometimes [found] in the upper forearm”. This can sometimes cause dilation of the distal radial artery “just enough to assist in cannulation”.

Narayan also suggested using a needle as a guide during cannulation, stating that it can be used “under ultrasound to push through clots or calcifications into a better part of the artery prior to advancing the wire”. He positied that cannulation should be performed “with haemostasis in mind”.

It was not just presentation sessions that featured during the American Society of Diagnostic and Interventional Nephrology (ASDIN) 19th Annual Scientific Meeting (17–19 February, Orlando, USA). Among the several hands-on elements of the conference were tutorials on the “one-minute check” for dialysis access as well as a cannulation simulator.

Deborah Brouwer-Maier (Transonic, Ithaca, USA) spoke to Renal Interventions during the session to explain the utility of and rationale behind the one-minute check. She noted that it is the physical examination recommended by the Kidney Disease Outcomes Quality Initiative (KDOQI) for checking a vascular access. She outlined that it is a “look, listen and feel” standardised test initially used and published by Gerald Beathard (University of Texas Medical Branch, Galveston, USA), who has featured it as part of the core curriculum with ASDIN.

The check includes “an arm elevation test, where the fistula is raised to see if it collapses— if it doesn’t collapse, it indicates the area of stenosis”. Also part of the check is “an augmentation test where you occlude to check the inflow”. Brouwer-Maier noted that it was a work group sponsored by the Fistula First Initiative that helped develop the method. It was designed to be performable by anyone from a clinician through to a dialysis technician nurse and even a caregiver. With that in mind, it was modelled on CPR checks that can be performed quickly and easily.

Brouwer-Maier made the case for the check: “When you talk to staff, most do not even take that minute to assess the access. Then, they cannulate the access and run into problems—if you do the one-minute check first, it reduces cannulation complications. You will know if the access is working, whether there is an aneurysm, an area at risk for a fatal access bleed, or an infection. You will feel the vessel and the thrill, listen to it and know whether there is a stenosis. It increases the chances of a successful cannulation in just one minute.”

Beyond educating at ASDIN, Brouwer-Maier said the aspiration was to take the check global. Centres without ultrasound may derive particular benefit, she suggested, though it also has a place in more fully equipped clinics. Cannulation mapping, demonstrated at the session by Forest Rawls (Emory Healthcare Dialysis Clinics, Atlanta, USA), was another way to assess the best approach to a given cannulation procedure.

Also featured during the Sunday hands-on sessions was a novel device for identifying what constitutes skilled cannulation. Joseph Ravi Singapogu (Clemson University, Clemson, USA), who led the team that developed the cannulation simulator, was on hand to explain how it allows the angle and pressure of a cannulation procedure to be evaluated in real time. “We have ‘sensor-ised’ cannulation: rather than the subjective opinion of a dialysis techni- cian, the expertise will be measured by sensors,” Singapogu said. “The goal is to help improve skill—and if you cannot measure, how can you track skill progress?”

“The pressure is a really big one,” Brouwer-Maier added. “When I used to do “cannulation camp”—training with a fake arm—all I could do was try to figure out how tightly a trainee was holding the needle to understand how much pressure they were applying. The simulator is a way for the trainee themselves to know when the pressure or angle is wrong while they perform the procedure.”

Brouwer-Maier and Singapogu were united in saying that they hoped the simulator would end the use of patients as practice models. “If we were physicians,” Brouwer-Maier said, “that would not be happening.”

Singapogu stated in summary: “You are only as strong as your weakest link. Is cannulation that weakest link?” The simulator, he hopes, will make it easier to answer that question in the negative.

In one of the select presentations at the ASDIN 2023 meeting to receive a mid-lecture round of applause, Victoria Teodorescu, associate professor of vascular surgery at Emory University (Atlanta, USA), posed the question: should nephrologists create surgical arteriovenous fistulas (sAVFs)? The rapturous response came as she answered in the affirmative.

THIS RESOUNDING ANSWER, which began the presentation, “needs a little bit of explanation,” Teodorescu stipulated. She then drew up numbers illustrating just how many patients on dialysis and requiring access there are in the USA. Taking information from the United States Renal Data System Annual Data Report, she pointed out that the number of patients receiving in-centre haemodialysis in the USA almost doubled between 2000 and 2020 from around 250,000 to around 500,000. This raises the question, she suggested, of “who exactly is going to do the access surgery?” for this expanding patient population. The solution, she suggested, may lie with nephrologists.

Historically, the surgeries necessary for haemodialysis access have been done by general surgeons, Teodorescu said. This made sense because general surgery training included a lot of vascular education, but more recent surgical training has seen this “drop off quite significantly, especially in arteriovenous (AV) access”, noting a 15-year decline (p=0.0218) according to the Accreditation Council for Graduate Medical Education (ACGME) Review Committee for Surgery. Teodorescu notes that the committee designates 10 dialysis accesses as the defined category minimum number for general surgery residents—something she says is “extraordinarily minimal experience”.

“Not all programs are created equal,” she continued, making use of the National Resident Report in the US for 2021–2022 to argue that “there are programmes where they do very little dialysis access”. Teodorescu said that, in 2022, 63 residents graduated from the 0+5 integrated vascular surgery training program, which she said was a “tiny, tiny number to do all of vascular surgery”— particularly when many showed a greater interest in aneurysms and lower extremities than dialysis access. “Just because you have finished with this particular training does not mean you know a lot about dialysis access,” she posited.

“This is not to say that we do not finish our fellows with extremely broad interventional skills, including aortas and other lower extremity interventions— other cases requiring a high degree of catheter skills,” Teodorescu said, “but we do not really have any education in dialysis itself or what is happening in the unit. We have surgeons adept in the techniques of vascular surgery but not necessarily in renal failure.”

Next, Teodorescu turned to the ASDIN recommendations for training nephrologists to bridge the gap she identified. She concurred with them, particularly in their urging the improvement of competency-based education “in all aspects of dialysis, including questions on board exams”. Teodorescu stressed this point especially in light of the fact that, in her view, future nephrologists will be charged with the responsibility for access in the dialysis unit.

The next recommendation with which she concurred was to ensure that fellows receive sufficient training in placing temporary dialysis catheters. Fellowships in interventional nephrology, she said, are also important. Access requires knowledge of dialysis, renal failure, and surgery, as well as intervention skills, she said: “We must develop a cadre of specialists who know everything about surgery, intervention, and what is going on in the dialysis unit—someone who knows why we might be having difficulty cannulating. We need the access specialist.”

This, she concluded, will pave the way for studies that will more effectively assess when surgery or intervention is the appropriate clinical decision. “We do not really have that right now,” Teodorescu remarked, “and until we each come out of our silos and know everything there is to know about everybody else’s field – nephrology, interventional nephrology and vascular surgery, we will not be serving our end-stage renal disease patients well.”

Speaking exclusively to Renal Interventions after the presentation, Teodorescu stated: “Providing the right access for the right patient requires a much broader set of skills than what any of our current training paradigms can provide. The difficult task of creating and maintaining dialysis access belongs in the hands of a new type of specialist, fully trained in surgical and interventional techniques as well as medical care of renal failure patients.”