Even with new data, the future of bioresorbable scaffolds remains in flux. At TCT 2018 in September, Reva Medical and Abbott Laboratories painted differing pictures with their respective bioresorbable scaffold studies. What now?
Dr. Lukasz Koltowski from the Medical University of Warsaw in Warsaw, Poland, presented new data from Reva Medical's "Fantom STEMI" pilot study. The study showed procedural success and clinical utility of the Fantom bioresorbable scaffold in nine patients with acute ST-segment elevated myocardial infarction (“STEMI”) heart attacks.
"Many heart attack patients are young with single blockages in their arteries, and the Fantom bioresorbable scaffold creates an opportunity for recovery without the risk of a permanent metal drug-eluting stent,” Dr. Koltowski said during a TCT presentation.
Reva Medical CEO Reggie Groves says the STEMI results are encouraging, but admits they provide limited information.
"Fantom may work better than metal stents in these patients primarily because the lesions are soft, which is good for scaffolds," she said. "And the vessel that contracted during the attack relaxes over time. Scaffolds may adjust to this relaxation better."
Dr. Yuichi Saito from the Yale University School of Medicine in New Haven, Connecticut, presented Fantom's two-year clinical results. Results showed a low 5% rate of Major Adverse Cardiac Events and a single, very late scaffold thrombosis event for a rate of 0.4%.
Abbott, which has arguably generated the most attention in the bioresorbable scaffold space, presented less encouraging results in its Absorb IV randomized trial. The study expanded on prior trials by including patients with biomarker-positive acute coronary syndromes.
Like last year's trial, Absorb IV showed a numerically higher risk compared to its Xience drug-eluting stent. Despite better patient and lesion selection and improved technique, 30-day and one-year rates of MI, ID-TLR and device thrombosis tended to be greater with Absorb than with Xience, the study reported.
Although Abbott's study affirms the end of Absorb, bioresorbable scaffolds have a presence in the European market. In June, Reva Medical received CE Mark approval for its full Fantom Encore product line, which is Reva's third-generation coronary bioresorbable scaffold. In July, it received CE Mark approval for its Motiv bioresorbable scaffold — the first drug-eluting bioresorbable scaffold to receive CE Mark approval for treatment of below-the-knee peripheral artery disease.
Amaranth Medical's Fortitude sirolimus-eluting bioresorbable scaffold (CE Mark application submitted, not yet approved) showed a high clinical device success rate (98.4%) in studies conducted in Columbia and Italy. Patients had symptomatic coronary artery disease and underwent percutaneous coronary intervention (PCI). Results showed low MACE rates (4.9%), low angiographic binary restenosis (1.6%) and high levels of strut coverage (96%) and scaffold stability at nine months. Amaranth is currently conducting studies for its Magnitude and Aptitude scaffolds.
Biotronik's Magmaris, a resorbable magnesium scaffold, received CE mark approval in June 2016. A review of 1,000 implants performed by 413 physicians across 32 countries showed 98.8% of scaffolds successfully implanted. About 96% of the participants rated the product as "good" or "very good." In up to 78% of cases, Magmaris outperformed a competing product in deliverability and vessel conformability.
One difference between Absorb and Boston Scientific's Renuvia, which also stopped production last year, is material. Absorb and Renuvia are both made with off-the-shelf poly-L-lactic acid (PLLA) polymer.
Reva Medical's scaffolds use Tyrocore, a proprietary tyrosine-derived polymer designed specifically for vascular scaffold applications. The polymer is radiopaque, which makes Fantom visible under X-Rays.
"We spent 10-plus years making that polymer from scratch," Groves said. "We explored different characteristics and levels to get different performance characteristics."
Magmaris is a fully bioabsorbable magnesium scaffold with a sirolimus-eluting bioresorbable PLLA coating. With a 150 mcm strut thickness, it's thinner than Absorb, but thicker than Fantom's 125 mcm or Fantom Encore's 95 mcm.
Biotronik states the Magmaris magnesium backbone minimizes recoil following a procedure, which means the scaffold withstands external force within the vessel. This property ensures the vessel remains open following implantation.
Slower adoption, greater opportunities
Abbott's decision to pull Absorb from the market, combined with Boston Scientific's decision to discontinue its Renuvia bioresorbable stent program, slowed down potential U.S. adoption and created some skeptics. However, Groves believes many physicians understand the technology's potential.
"Absorb's clinical performance did not align with promises Abbott made," Groves said. "While physicians are disappointed, nearly all believe bioresorbable is the right answer."
In response to a prospective need for more clinical evidence, Reva Medical is ramping up postmarket registry studies. It's also directly marketing its products in Europe. In November 2017, Boston Scientific elected to let its right to negotiate for exclusive distribution expire.
At the time, Boston Scientific had just released Synergy, a drug-eluting metal stent, which was competing quite well with other major players. That success, combined with Abbott's Absorb III study results, prompted Boston Scientific to put its bioresorbable stent program on hold.
The developments over the past year put Reva Medical and Biotronik in favorable positions. As they move forward with their products, and until 5- and even 10-year studies become available, the future remains uncertain, but not without hope.
"As was true in the movement from bare metal to drug eluting stents, a first-generation novel technology often stumbles," said Groves. "It's getting through to the next generation that makes a difference. We believe we're leading that transformation."