FDA investigates stent “shrinkage” in Boston Scientific’s Ion, Promus stents, others

The FDA is investigating reports that the thinner design of next-generation drug-eluting stents, including Boston Scientific’s (NYSE:BSX) Ion and Promus models, might be prone to deforming after implantation.

At least two studies and one case study presented at a recent cardiology conference reported incidents in which either a Boston Scientific Ion or Promus stent deformed after it was deployed inside a coronary artery.

“FDA is actively working with manufacturers, including Boston Scientific, to better understand longitudinal stent deformation with respect to its causes, predisposing underlying anatomic conditions, operator techniques that can reduce the likelihood of its occurrence, and treatment strategies should it occur,” the agency told Reuters in a email.

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Although there’s been only one reported incident of deformation involving a Promus stent from among more than 4,600 implantations in clinical trials, according to the federal watchdog agency, “an unspecified number of significant adverse events had been reported to the agency,” according to the news service.

“At this time, additional data collection and analyses are ongoing, but the information available to date indicates that the Ion paclitaxel-eluting platinum chromium stent remains safe and effective when used for its approved indications,” the FDA said, according to Reuters.

An Irish study published earlier this month found that thinner stents may have lower longitudinal strength, potentially leading to stent thrombosis and a “catastrophic late complication” and leaving the target lesion unprotected, according to scientists at the Belfast Health & Social Care trust.

Dr. Cindy Grines, editor of the Journal of Interventional Cardiology, detailed a case in the journal’s October issue involving “marked shortening, deformation and accordion of the Ion coronary stent,” something she claimed she hasn’t seen before in 25 years of practicing cardiology.

The stent involved in the case shortened by about 35 percent, Grines wrote.

“We believe that accordion of the stent caused technical difficulties in rewiring the vessel and ultimately stent thrombosis, [and] thus is of serious concern. Although recent reports from Europe noted this phenomenon in the Element and Omega stents (similar family of stent designs), to my knowledge this is the first published case in the stent approved in the United States, the Ion stent,” she wrote. “Although this shortening phenomenon may just require an additional stent to ensure adequate coverage of the lesion, in our case it appeared that the stent may have deformed and involuted, further compromising the lumen and preventing additional device interventions.”

Citing data from a second bench test conducted by Abbott (NYSE:ABT) “showing that the Element family of stents (including the Omega and Ion) may shorten up to 46 percent under the force that an interventional cardiologist may exert to advance a post-dilation balloon or intravascular ultrasound device, Grines called the results “very disturbing.”

“Hopefully, there will soon be new recommendations regarding the use of stents of this particular design for our community of interventional cardiologists. Until further data are available, our institution will use the Ion stent cautiously, and only when alternatives are unavailable for the size under consideration,” wrote Grines, who is vice president of clinical and academic affairs at Detroit Medical Center’s Cardiovascular Institute and a professor at Wayne State University.

The Irish researchers looked at stents made by Boston Scientific and Abbott, as well as stents from Medtronic (NYSE:MDT), Johnson & Johnson (NYSE:JNJ) and Biosensors International Group. Their study compared Abbott’s Xience V’s and Xience Prime’s 81-micrometer thickness, for example, with J&J’s 140-micrometer Cypher and Cypher Select Plus.

“Stents have a lot of different properties, which vary from one to another,” noted New York Presbyterian Hospital and Colombia University Medical Center director of cardiovascular research Dr. Gregg Stone during a conference call discussing the Belfast report. “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.”

But the problem may not be a design flaw, Stone told Reuters, citing instances in which the balloon used to implant the device or the guide wire that carries the stent catch or pull on the stent and deform it.

“It can happen with any stent if you’re aggressive enough with it,” he said. “The metal is very thin – it’s 3/1,000 of an inch thick, so depending on the material and configuration … some are more prone (to deformation) than others.

“It seems to be a rare phenomenon. Millions of these are implanted and there are just a handful of these cases,” he said.

“Someone needs to put the cases together and look at them and decide about the signal of adverse events,” Mayo Clinic cardiologist Dr. David Holmes told Reuters, noting that the exact cause of the problem is still unclear. “This absolutely warrants more study.

“If it’s a mechanical problem, it needs to be fixed mechanically. If it’s a procedure issue, we need to make sure the initial deployment is ideal and we can do that by using imaging studies,” Holmes said.