Cleveland Clinic researchers report that at two years, patients who received a type of dissolving coronary stent fared somewhat worse when compared to patients receiving drug-eluding metal stents, but researchers say the study’s results may not ultimately portray the potential for the stent’s future success.
The ABSORB III trial compared the Absorb everolimus-eluting bioresorbable vascular scaffold (BVS), which is designed to gradually dissolve over three years after being placed in a heart vessel, to the Xience everolimus-eluting stent (EES). The trial enrolled 2,008 patients at 193 centers. Patients were randomized to either BVS (1,322) or a drug-eluting metallic stent (686 patients). The study’s primary endpoint was target lesion failure, as measured by a composite of cardiac death, target lesion heart attack and ischemia-driven target lesion revascularization. That occurred in 10.9 percent of patients in the BVS arm compared to 7.8 percent of patients in the EES arm.
Researchers caution that there are two significant limitations to the data. A considerable number of patients in ABSORB III (19 percent) had stents placed in vessels that were smaller than what the inclusion criteria dictated. FDA instructions for use indicated the BVS should not be implanted in very small vessels. A subgroup analysis showed these patients had worse outcomes than those who had stents placed in vessels at least 2.5 millimeters in diameter, which is the recommended size. When excluding small vessel patients, results showed the primary endpoint occurred in 9.3 percent of BVS patients and 7 percent of EES patients, a difference that was not statistically significant. Bioresorbable scaffolds are plastic and require thicker struts than their metal counterparts, which may contribute to the poorer outcomes in small vessels.
Additionally, BVS implantation technique has evolved and improved since the start of the trial. Evidence suggests that high pressure dilation of the vessel after implantation of the scaffold improves outcomes for BVS patients. However, at the initiation of the trial, this practice was not well-known and thus not consistently performed among study researchers.
“As we gain experience, we are refining the best practices for these stents and expect to see more favorable outcomes,” said Stephen Ellis, MD, of the Cleveland Clinic, who led the study along with Dean Kereiakes, MD, from Christ Hospital in Cincinnati.. “We don’t yet have the data to determine whether bioresorbable stents will be better for patients. At two years, the stents have not fully dissolved, so we will have to wait for longer term results.”
Every year, about 600,000 new patients have metal coronary stents implanted to treat a vessel blockage. While they reopen blood flow in patients with clogged arteries, traditional stents can have some drawbacks, such as restenosis, which occurs when the blood vessel narrows again after the stent is implanted. The formation of blood clots on the stents is also a concern, as well as the fact that stented blood vessels lose their natural capacity to expand under certain conditions. Bioresorbable stents are designed to diminish the problems of restenosis and clot formation, as well as avoid the need for the patient to be on long term anti-clotting medication.
The research was presented at the American College of Cardiology’s 66th Annual Scientific Session.
Working in collaboration with the FDA, a landmark analysis combining ABSORB III study with another study called ABSORB IV (which began after the establishment of implantation techniques) to attempt to demonstrate superiority over drug eluting stents has been extended. It will now start three years after device implantation when the BVS is expected to be completely absorbed, and follow patients for an additional four to seven years.
The FDA approved the Absorb BVS in July 2016 and implantation guidelines are included in its instructions for use.
Dr. Ellis is a paid consultant for Abbott Vascular, which makes the Absorb BVS.