Stent Shrinkage

I heard a new term related to coronary stents today: "shrinkage." Unlike the manly "shrinkage" of the Seinfeld show, it seems new polymer stents can also suffer from "shrinkage:"

(TheHeart.org) Dr Patrick Serruys (Thoraxcenter, Rotterdam, the Netherlands) presented results of the ABSORB trial during a late-breaking session at the American College of Cardiology 2007 Scientific Sessions today. In the trial, 26 patients received the new stent—which, it is hoped, will completely dissolve after 12 to 18 months—and there was no evidence of stent thrombosis after six months, together with a low rate (3.3%) of ischemia-driven major adverse cardiac events (MACE).

But late loss and restenosis were greater with the bioabsorbable stent than with current drug-eluting stents, and Serruys said the 15% shrinkage seen with the new stent may be to blame for these findings. He is hoping that the modification of the stent design—due to be completed by the end of the summer—will solve this problem. "This may be the beginning of a new era. I'm convinced of it," he commented.

However, chair of the late-breaking press conference, Dr Spencer King (Emory University School of Medicine, Atlanta, GA), was more circumspect: "Our early experience with polymer stents was terrible in experiments in pigs. This trial is in only 30 patients, with short follow-up. However, on the plus side, we didn't see any inflammation. Time will tell."

My guess? Shrinkage has already killed this current generation of bioabsorbable stent, but a second-generation polymer stent is already in the works...

-Wes

Another Biodegradable Stent Debuts

And just when the cardiovascular surgeons thought they might wrestle back the coronary revascularization business, a new completely bioabsorbable coronary stent released its first early clinical results today. This stent is produced by Bioabsorbable Vascular Solutions, Inc. (BVS), a Guidant (now Boston Scientific spun off to Abbott Vascular during the earlier Guidant acquisition by Boston Scientific):

The new BVS stent is made of a polymer that dissolves into lactic acid over two to three years. Lactic acid is a naturally occurring substance in the body, produced after exercise. It breaks down into carbon dioxide and water, and is absorbed by the body.

Unlike earlier bioabsorbable coatings over a bare metal stent, like the earlier Biomatrix stent, no bare metal exists in this stent. Of note, the stent also contains everolimus, and elutes this drug over an estimated 120 days. These patients are part of the ABSORB clinical trial enrolling up to 60 patients in Belgium, Australia, Denmark, France, the Netherlands, New Zealand, and Poland. While the initial results seem promising, there are a few caveats worth mentioning:

• These stents have no long-term track record and have not yet begun trials in the US, to my knowledge, but the international experience will form a basis to begin the first US trials, if successful.


• The stents will have an initial inflammatory reaction after implantation since the polymer is a foreign body. As such it is still subject to restenosis, though the everolimus should help reduce this inflammatory response.


• It should have better imaging in MRI scans and CT scans since the polymer will not cause the reflectance artifact like metal stents.


• While the absorbable nature of the stent is intriguing, the mechanism of late-stent thrombosis is unknown, so long-term studies on anti-platelet agents will still be needed, especially since the stent is drug-eluting for only 120 days of its 2-3 year existence in the coronary artery. It's just too early to claim that these new stents will reduce in-stent late thrombosis risk yet.

Nonetheless, it is refreshing to see some new news on the coronary stent front that might make the debate between bare- and drug-eluting metal stents a mute one.

-Wes