A 12-month update on a study investigating the use of the Absorb drug-eluting scaffold (Abbott) in below-the-knee arteries (ABSORB BTK) indicates that bioresorbable vascular stents can achieve good immediate angiographic results and promising 12-month patency.
The update was presented by Ramon Varcoe, Sydney, Australia at the 2016 Leipzig Interventional course (LINC; 26–29 January, Leipzig, Germany).
Metal drug-eluting stents can achieve good results, Varcoe told the audience. “I have been using them for a long time because they work,” he said, “and three previous randomised controlled trials have shown that drug-eluting stents are clearly superior to standard therapy of bare metal stenting or plain balloon angioplasty.” However, “these devices are far from perfect”. Issues include late thrombosis rates, fixed and rigid blood vessels post-deployment, artefacts on imaging and that they are impediments to future interventions.
Absorb is a bioresorbable everolimus-eluting scaffold with a multilink design and circumferential hoops. The scaffold (150µm strut thickness) has straight connection bridges and radiopaque platinum markers to ensure accurate placement.
The Absorb stent represents “a new concept, a new paradigm in the way that we stent below-the-knee vessels,” Varcoe told delegates. “Rather than leaving behind a metal implant which makes the vessel rigid, we are trying to restore the function of that vessel, and by doing so reduce late occlusive events.” Thus far, Varcoe said that the research team have observed plaque regression and luminal gain as the stent structure dissolves. The structure itself is “mostly taken away in the 12–18 month window and is completely invisible by three years,” he noted.
The single-centre study enrolled patients with chronic lower limb ischaemia with Rutherford classification 3–6. These patients needed to have a life expectancy of more than one year and de novo lesions of >60%. The team only wanted to use two scaffolds in any one lesion, so lesion length was capped at 5cm, and the diameter range was 2.5–4mm. Treated inflow lesions were accepted and the trial focused on the tibial arteries (although it did include the distal popliteal).
At first the team focused on safety and feasibility, with the primary safety endpoint as major adverse event rate at 30 days and the feasibility endpoint as technical success. “It quickly became apparent that this was a safe device and easy to deploy in this part of the body, so we then focused our attention on clinical endpoints,” Varcoe said. Clinical improvement was measured by primary, assisted primary and secondary patency rates, as well as target lesion revascularisation and total vascular regeneration (measured using duplex ultrasound follow-up at one, three, six and 12 months, with a peak systolic velocity ratio of >2). The team also looked at improvements in patients’ Rutherford-Becker Class classifications.
Thirty-seven limbs (in 32 patients, age range 65–97 years) have so far been treated with 48 scaffolds, 73% of which exhibited critical limb ischaemia and 27% intermittent claudication. Mean lesion length was relatively short at 18.7±11.1mm. There was a range of vessels treated across all of the below-the-knee arteries, although most were in the proximal third of the tibial arteries, particularly the tibial-peroneal trunk, “whose length and diameter really does suit this device,” Varcoe said.
Varcoe reported 100% procedural success with one acute occlusion (day one, no dual antiplatelet therapy, which was “an oversight” on the part of the investigators). Four deaths occurred outside of 30 days and were unrelated to the device. Sustained clinical improvement (measured by Rutherford-Becker category) was seen in 73% of patients. Primary patency and assisted primary/secondary patency were “a remarkable” 95.5% and 100%, respectively, Varcoe reported. The study team achieved 100% salvage, while target lesion revascularisation and total vascular regeneration rates were both 4.5%.
Varcoe compared the results with existing randomised control trials evaluating infrapopliteal lesions treated with plain balloon angioplasty, bare metal stents, drug-eluting stents or drug-coated balloons. He told the audience that the standard therapy arms—plain balloon angioplasty and bare metal stenting—of the trials cluster around primary patency rates of approximately 50–60%. Drug-eluting stent results tend to cluster slightly higher; at approximately 80% primary patency. The ABSORB BTK results sit above all of these at 95.5% primary patency.
“Vascular restorative therapy with a bioresorbable scaffold offers several advantages over metal drug-eluting stents,” Varcoe concluded. “Bioresorbable scaffolds can be implanted safely within the tibial vasculature, and excellent immediate angiographic results and promising 12-month patency can be achieved.”
“I think that the idea of leaving nothing behind is a great concept and one that we all believe in at this point in time, but most of us know that there is a need for stent-like scaffolding in many of our patients,” Varcoe suggested. “This particular device serves both purposes—stent-like scaffolding and leaving nothing behind.”