Metal vs 'Plastic' for Disappearing Drug-Eluting Stents Debated

October 13, 2015

SAN FRANCISCO, CA — Drug-eluting stents (DES) made of bioresorbable polymers may be all the rage, but some investigators see advantages in such "disappearing" coronary stents made of metal. In a small single-arm study reported here at TCT 2015, a sirolimus-eluting stent with a scaffold made of a magnesium alloy performed angiographically about as well as durable-metal and polymer DES over 6 months in patients with symptomatic or silent ischemia[1].

Only de novo lesions were treated. There were no cases of in-stent thrombosis and only low rates of target lesion revascularization that were "comparable to [those of] other absorbable scaffolds and permanent drug-eluting stents," said Prof Michael Haude (Lukaskrankenhaus Neuss, Germany) when presenting the study, called BIOSOLVE II. Haude is also lead author on its simultaneously published report in the Lancet.

The 1-Year Disappearing Act

Prof Michael Haude

Importantly, Haude told heartwire from Medscape, the metal alloy of the investigational stent, DREAMS 2G (Biotronik), was formulated to be absorbed in about a year, in contrast to the 2 to 3 years typical of contemporary polymer bioresorbable stents. That period, he said, probably represents an "ideal balance" between early scaffolding needs in the target vessel and the later goal of "fairly complete absorption." And, he said, the process does not seem to evoke an inflammatory response any more than permanent metal stents, based on animal studies.

With the ABSORB series of trials and their featured everolimus-eluting polymer Absorb coronary stent (Abbott Vascular) taking a high-profile position at TCT 2015, and with burgeoning broader interest in bioresorbable stents, observers at the meeting compared "plastic" and "metal" as the stuff of scaffolds.

Functionally, "the big difference between the two devices is in the speed of absorption—1 year for metal and 3 years for plastic," Prof Pascal Vranckx (Hartcentrum Hasselt, Belgium), who wasn't involved in BIOSOLVE II, said to heartwire .

"This has repercussions for antiplatelet therapy," he said, in that dual-agent antiplatelet therapy may be needed for only a year with the DREAMS 2G but much longer with polymer stents. "It would have to be shown, but it's a hypothetical advantage of this device over the Absorb stent."

Two drug-eluting bioresorbable stents have the CE mark, Abbott's Absorb and the DESolve (Elixir Medical), according to Haude and his colleagues. Haude said the "first-in-human" BIOSOLVE II study will be shown to European regulators in hopes of becoming the third.

Late Lumen Loss in BIOSOLVE II

The study prospectively enrolled 123 patients at 13 PCI centers in Belgium, Brazil, Denmark, Germany, Singapore, Spain, Switzerland, and the Netherlands. They had de novo target lesions no longer than 21 mm and with an angiographic stenosis severity 50% to 99%. Patients were prescribed dual antiplatelet therapy for at least 6 months. Results of angiography, intravascular ultrasound (IVUS), and optical coherence tomography (OCT) were interpreted at a single independent core laboratory.

Mean late lumen loss at 6 months was 0.27 mm in the target segment and 0.44 mm within the scaffold itself. "The in-segment late lumen loss of DREAMS 2G is similar to that of polymeric scaffolds," write the investigators, "whereas the in-scaffold loss is within the upper range of late lumen loss in polymeric scaffolds and slightly higher than the loss with the latest iterations of Absorb and DESolve."

On the other hand, "late lumen loss is probably a moving target in absorbable scaffolds and has low relevance for prediction of long-term outcomes," note Haude and coauthors, "because in absorbable scaffolds late lumen enlargement (beyond 1 year) was reported."

IVUS showed comparable mean scaffold area immediately postprocedure vs 6 months (6.24 mm2 and 6.21 mm2, respectively) with neointima averaging only 0.08 mm2 in area. No intraluminal masses were detected by OCT, according to the group.

From the podium after Haude's formal presentation of the study, which showed the DREAMS 2G performing incrementally better than an earlier paclitaxel-eluting version of the device, Dr Dean J Kereiakes (Christ Heart and Vascular Center, Cincinnati, OH), said of the sirolimus-eluting version: "To me it looks like a successful iteration of the device." Kereiakes is co–principal investigator of the ABSORB III study of the Abbott polymer stent, which was also presented at TCT 2015.

Do the Intangibles Make a Difference?

At a briefing on the study for the media, Dr Dan Simon (University Hospitals Case Medical Center, Cleveland, OH) posited, "If you poll interventional cardiologists on what is the most important aspect of [coronary stents], it's deliverability. They want an easy, straightforward procedure to get the device to the lesion."

So with regard to the "plastic or metal" question, whether the DREAMS 2G, Absorb, or some other bioresorbable stent is acceptable to operators could well depend on its trackability and how comfortable it feels. "What material will get you closest to a durable metal drug-eluting stent that's [made of] cobalt-chromium [and is] best in class?" he said. "I think that's the question, and I think whoever makes the most deliverable scaffold will win."

Speaking with heartwire , Haude agreed that in the event that the DREAMS 2G is approved in Europe, the PCI community may decide based on "soft" criteria whether to prefer it or one of the other bioresorbable stents.

"When I get a new [stent], the first thing I do is take it out of the box, and feel it between my fingers—how does it feel? How slippery is it? You take one of the plastic ones and take this [magnesium-alloy] one, even if you are unbiased you will really feel a difference." The metal one, he contends, feels like the mainstay metal stents most operators trained on, and that would likely be a major driver of its appeal.

Vranckx said to heartwire that such subjective impressions do shape PCI operators' fondness for one stent or another and that "acting like a regular stent is important" for new drug-eluting incarnations. But with modifications to scaffold design and strut thickness, probably "it's only a matter of time" before the Absorb and other polymer stents are as trackable and familiar-feeling as the DREAMS 2G.

BIOSOLVE II was funded by Biotronik. Haude discloses receiving grants and lecture fees from Biotronik, Abbott Vascular, Cardiac Dimensions, Medtronic, Volcano, and Lilly. Disclosures for the coauthors are listed in the paper.

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