Design Flaw Poses Potential Threat to Shrinking Drug-Eluting Stents

In the quest for increasingly thinner, smaller, and more-flexible stents, medical device designers may have compromised structural integrity in some current-generation drug-eluting stents (DES). And as the problem of longitudinal compression reaches buzz-worthy status, the design flaw could soon prove to be a distinct market disadvantage.

Published online last month in the medical journal EuroIntervention, a case series conducted by two UK physicians brought the issue of longitudinal compression in some newer stents to light. The series examines three different patients' experiences with three different DES: Biosensors International's biolimus-eluting BioMatrix stent, Boston Scientific's everolimus-eluting Promus Element stent, and Medtronic's zotarolimus-eluting Endeavor stent. Based on these studies, the doctors reported issues with compression along the longitudinal access as well as compromised longitudinal strength resulting from distortion caused by larger guide catheters, according to theheart.org.

These design defects can be traced to stent manufacturers' attempts to produce stent platforms with increasingly thinner struts designed to better navigate tortuous and calcified coronary arteries. "The main focus for many years has been to produce stents with radial strength, so that they're not compressed in a circular fashion," Simon Walsh, one of the physicians involved in the study, told theheart.org. "The longitudinal issue hasn't really been on anybody's radar until now. Longitudinal strength has never been one of the defining features of the stents. We've always wanted the stent to support the vessel, to be deliverable, and deliver the drug, but nobody would have ever come to a stent company five years ago and asked for a stent that can't be compressed longitudinally. It was never part of the design game before."

On the heels of this case report, organizers of the upcoming Transcatheter Cardiovascular/Therapeutics (TCT) meeting have added the subject of longitudinal compression in cardiac stents to the conference agenda, further brightening the spotlight on the emerging design flaw. "Stents have a lot of different properties, which vary from one to another," Gregg Stone, director of TCT, said in a conference call ahead of the meeting, according to Bloomberg BusinessWeek. "Some stents will be more prone to this complication than others. The question is to understand how frequent it is, when does it occur, how to prevent it, and how to manage it." Longitudinal compression can lead to stent thrombosis or possibly restenosis, Stone adds.

Although longitudinal compression, at present, appears to be a rather uncommon occurrence, it could have an impact on next-generation stent designs as well as current-generation stent sales. If more instances are found or negative publicity abounds, for example, Medtronic, Biosensors International, and Boston Scientific--as the companies named in the study--could soon be embroiled in a PR nightmare. Boston Scientific's stent, in particular, was cited by the physicians of the UK study as demonstrating more vulnerability to longitudinal compression than other stents. Seeing an opportunity, competitor Abbott Laboratories has been quick to pounce on this news and already use it "as a marketing advantage," according to Bloomberg. A spokesperson for Abbott told Bloomberg that its Xience DES features a stent design that withstands such pressure and has had "virtually no reports" of longitudinal compression.

As for next-generation drug-eluting stents, however, engineers should be cognizant of longitudinal compression when designing new platforms and take measures to prevent it from occurring. For more information on stent design, check out the recent MPMN special feature, "Shrinking Stents Strut Their Stuff." --Shana Leonard