Expert panel discusses challenges of bioabsorbable stents

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Image Source: Abbott

Washington, D.C.—Representatives from industry, the FDA and clinical practice came together here last week at the Cardiovascular Research Therapies (CRT) 2009 conference to discuss the future of bioabsorbable stents, analyzing the current clinical and regulatory complications, and potential benefits of the new technology.

Renu Virmani, MD, cardiovascular pathologist and medical director at CVPath, International Registry of Pathology in Gaithersburg, Md., said that stent fractures are still important considerations for bioabsorbable stents, and "if they fracture, how often and what is the effect." She noted that inflammation and total degradation also are considerations for these new devices.

"Total degradation is important because you want to know how long the stent has been gone, so you have some idea how long you need to follow your patients," Virmani said.

In terms of the dual-antiplatelet therapy (DAPT) during the degradation period, Virmani said that there are certain aspects of therapy that cannot be learned from animal studies proportionately because animals heal at very different rates compared to humans. However, in this particular case, "we seem to find parallels between the human and animal studies, so the stents may be degrading at the same rate, and therefore, the rates may be similar. All this being said, if I was the patient, I would want two years of dual-antiplatelet therapy because I could be assured that the stent would have degraded by that time."

Panel moderator J. J. Popma, MD, from Beth Israel Deaconess Medical Center in Boston, raised the question about whether bioabsorbable stents will initially be more useful in interventions outside of the coronaries, such as the peripheral vasculature. Ron Waksman, MD, associate director of cardiology at the Washington Hospital Center in Washington, D.C., noted that his institution had some experience using the stents in pediatric patients born with pulmonary atresia.

"Tibial arteries and SFAs [superficial femoral arteries], where traditional stents are not doing well, could be another option for bioabsorbable stents," Waksman said. Virmani commented that industry will have difficulties developing a bioabsorbable stent that is clinically efficacious and safe for the SFAs.

"In my opinion, if this is not going to be a workhorse stent—gaining at least 20 percent of the coronary market—it would be very difficult to believe that industry will continue to provide funding," according to Waxman.

Eberhart Grube MD, chief of cardiology and angiology at the Heart Center Siegburg in Siegburg, Germany, who also consults for several stent firms, agreed with Waksman's perspective. "By our calculations, we need to capture 10 percent of the European coronary stent market share and 15 percent of the U.S. and Japanese markets to break even. Just to break even. So, it is going to be a coronary product, first and foremost," Grube said.

Richard J. Rapoza, PhD, division vice president at Abbott Vascular, which is trialing a bioabsorbable coronary stent, said the company still feels comfortable with a composite endpoint that includes revascularization, as well as evaluating major adverse cardiac events. "We will need to show some differences to currently used standards of care. For example, there could be scientific evidence, indicating the reduction in the duration of thienopyridine. At the end of the day, it needs to prove that it's at least as good as what we have now," Rapoza said.

A few panel members questioned whether bioabsorbable stents should be trialed against bare-metal stents, which caused the FDA spokesperson to balk. "If you have a bioabsorbable system that uses a drug, questions arise about the added benefits or risks of the drug," according to Ashley B. Boam, chief of the interventional cardiology devices branch at the FDA's Center for Devices and Radiological Health. "You still have to consider that there are risks, even if they are very low. If it turns out you could identify a population for bare-metal stenting, and if it turns out that bioabsorbable stents are comparable or better, then that would be taken into consideration."

"Fundamentally, the challenges are a balance of science between the inflammation, the hypersensitivity, the injury, along with the ability to keep the vessel open," commented Andrew Farb, MD, of the Office of Device Evaluation at the FDA's division of cardiovascular devices.

The panel, along with