Now You See the Stent, Now You Don't

Now You See the Stent, Now You Don't

MIAMI -- Some say bioabsorbable stents need more data, others say current drug-eluting stents are fine, but none of that mattered to the standing-room-only crowd who heard the latest research here on this novel technology.

The truth is that the current generation of drug-eluting stents have a good safety profile, with a very late stent thrombosis rate of about 0.5%.

But that was not the case when research began on bioabsorbable stents. Those were the days of first-generation drug-eluting stents, and even though DES revolutionized coronary revascularization, the advance came with two costs, Thomas Tu, MD, of Louisville Cardiology Group in Louisville, Ky., told MedPage Today at the Transcatheter Cardiovascular Therapeutics scientific symposium here.

"First, was the price, which was significantly higher than bare metal stents. Second, was the concern for longer duration of dual antiplatelet therapy," Tu said. "The fact that there were still questions about drug-eluting stents spurred further interest in perfecting this technique of opening blocked arteries."

Implanting a stent is an intentional injury to the coronary wall. It's a trade-off for unblocking the artery. Bare metal stents had no way of healing this acute injury, so, researchers developed stents with drugs that softened the acute intrusion.

This worked well for a while until it was evident that drug-eluting stents incurred a risk for late and very late stent thrombosis (after a year). Many pegged the source of the problem as the stent polymer, the drug carrier.

The next logical step was to develop a stent whose polymer would dissolve over time, leaving only a bare metal stent behind. In theory, this would solve the problem of the acute injury because the drug elutes early to help heal the endothelium and solve the problem of late stent thrombosis because the polymer disappears within 3 to 9 months.

How is this theory holding up under the research? Pretty good, discussant Antoine LaFant, MD, of the Hospital European Georges Pompidou in Paris, told MedPage Today.

"From this session, we can learn that bioabsorbable stents in humans have longer follow-up, from 3 to 5 years, which is quite reassuring in terms of the safety and efficacy," LaFant said.

Interestingly, LaFant and colleagues are pushing the envelope even further. They are developing a stent without a drug that disappears 3 months after implantation. "We take advantage of the positive remodeling resulting from the dismantling of the stent," he said. In preclinical studies, they have seen negative late loss at 9 months without any drugs. In July, they implanted the first human with this stent in a trial called ARTDIVA.

Patrick W. Serruys, MD, PhD, of Erasmus Medical Center in Rotterdam, The Netherlands, presented 5-year data from the all-comers LEADERS trial that compared two stents: the BioMatrix Flex, which has a biodegradable polymer that dissolves within 6 to 9 months and elutes biolimus (a semi-synthetic sirolimus analogue), and the Cypher Select, a first-generation sirolimus-eluting durable polymer stent that has been discontinued.

The BioMatrix Flex proved noninferior in the long-term to the Cypher in terms of major adverse cardiovascular events, and showed a significant reduction in very late stent thrombosis (0.66% versus 2.5%, P=0.003 for superiority).

Several bioabsorbable stents are approved in Europe, but none are FDA-approved.

Dual Antiplatelet Therapy

One of the theoretical advantages of the bioabsorbable stent is the potential to shorten the duration of dual antiplatelet therapy. But all studies of bioabsorbable stents so far have not veered from the recommended 12-month duration.

"How will we know if we can shorten therapy duration if no one will conduct a trial comparing 12-month duration with 6- or even 3-month duration," said Sigmund Silber, MD, of the Heart Center at the Isar in Munich, Germany, in an interview with MedPage Today.

Silber was involved in developing the original guidelines for dual antiplatelet therapy for the European Society of Cardiology. He and others looked at the data (no randomized trials), which suggested a threshold of 6 months would be optimal.

"The American's later became a little nervous and arbitrarily picked 1 year as the duration, but there are no data to support that," he said.

Interestingly, Silber and colleagues reviewed pooled data from the RESOLUTE global studies, which compared two second-generation drug-eluting stents with permanent polymers. About 1,000 of the 5,000 patients had interrupted or discontinued their dual antiplatelet therapy. Those who discontinued therapy after at least 1 or 3 months did not have any stent thrombosis at 1 year. But those who discontinued therapy in less than a month did have stent thrombosis within a year, he reported here at the TCT meeting.

"This was a very surprising finding, and although this post hoc analysis must be interpreted with caution, it does put the duration of dual antiplatelet therapy with a durable polymer in an interesting perspective," he said.

Silber is not convinced that the polymer is solely responsible for late stent thrombosis. He has yet to see convincing data. He also doubts he would use a bioabsorbable stent because the latest generation of drug-eluting stents are very good and without a shorter duration of antiplatelet therapy, he doesn't see an advantage.

Another concern is the price, which is about four to five times that of current drug-eluting stents. In Europe, these stents are not reimbursed, Silber said.

When, Not If

There seemed to be more people who believed that it's only a matter of time before drug-eluting stents with bioabsorbable polymers become routine in the cath lab. The evidence so far is good for relatively simple lesions, but these novel stents have not been tested in complex lesions, bifurcations, left main disease, heavily calcified lesions, total occlusions, and tortuous vessels, noted Ricardo Costa, MD, of the Cardiovascular Research Center in Sao Paulo, Brazil, in an interview with MedPage Today.

"I believe bioabsorbable stents have the potential to be incorporated in a significant proportion of PCI cases, but it will be very difficult to replace the low-profile modern drug-eluting stents we have today because they have very good results," he said.

Trying to convince interventional cardiologists to use bioabsorbable stents instead of those with a durable polymer may be challenging.

"I think saying that we have a tool that has the same advantages of the current stents but is a little better is probably not the best way to think about bioabsorbable technology," he said.

Tu suggested that bioabsorbable stents might find a home in other vascular beds, such as the superficial femoral artery, which is in constant motion and has resisted for the most part efforts from conventional stents.

He also said that it might be possible to use a completely bioabsorbable stent to deliver drugs to vulnerable plaque. The drug would heal the soft plaque and there would be no concomitant risk of having a permanent metallic stent in the body.

http://www.medpagetoday.com/MeetingCoverage/TCT/35552