Sometimes the best information about the performance of medical technologies comes from autopsies. A new study that pathologically assessed drug eluting stent (DES) fractures puts the rate of broken stents at 29%, far above the 1% to 2% previously reported.
First-generation DES stents, longer stents, and specifically the Cypher stent made by Cordis (Miami Lakes, Florida), a unit of Johnson & Johnson (New Brunswick, New Jersey), were all found to be more apt to break than the Taxus DES stent made by Boston Scientific (Natick Massachusetts).
"If I were a patient, I would ask 'Why are you using Cypher when there are better stents on the market?' I wouldn't let them put either the Cypher or Taxus into me," said the study's principal investigator Renu Virmani, MD, president and medical director, CVPath Institute (Gaithersburg, Maryland).
Virmani and colleagues studied high-contrast film-based radiographs of 177 consecutive lesions from a CVPath DES autopsy registry. Stent fractures were graded on a scall of I to V and adverse pathologic findings (thrombosis and restenosis) were assessed histologically.
"Fractures usually occur when the artery was kinked or bent and then straightened when the DES was implanted," Virmani told Medical Device Daily. "Those sites have excessive stress and the stress is usually in the middle. And if it's overlapped, the incidence is even higher. When you overlap, there is more strength, but where the overlap finishes, it will fracture."
Specifically, in overlapping stents, most fractures were observed within a 5 mm distance from the overlapping zone.
Stent fracture was documented in 51 lesions. Longer stent length, use of Cypher, and longer duration of implant were all identified as independent risk factors of stent fracture.
"Most of the fractures in the Cypher stents were located in flexible N-shaped, undulating longitudinal inter sinusoidal-ring linker segments, whereas in Taxus Express stents, fractures were observed in the straight longitudinal inter crown linker or the modular ring portion," Virmani and colleagues wrote in the current issue of Journal of the American College of Cardiology.
Stent fractures can cause thrombosis (blood clots) and restenosis (a narrowing of the blood vessel, restricting the flow). Virmani found that although slight fractures didn't seem to have adverse effects on patients, almost three quarters of the fractured stents studied revealed signs of scar tissue or blood clots.
"Of those 51, we had nine cases with severe fracture, meaning the stent is broken through and through," she said.
As an example, the team cited a case of a 60-year-old man with a grade V Cypher stent fracture who reported having chest pain 60 days after stent placement and underwent angiography. Stent thrombosis was found and treated by balloon angioplasty followed by bypass surgery. But the patient later died of undisclosed surgical complications.
Another man, 58 years old, died of subacute stent thrombosis 11 days after implantation with the Cypher stent. In that case there was a complete separation of the Cypher stent distal to the site of overlap with thrombotic occlusion. At the site fracture, the stent was under expanded, and a blood clot was observed in the vessel.
Virmani pointed out that her team studied first-generation stents, but that some of the newer generation DESs are not yet available in the U.S.
"The strength of stents has to change and the design has to change," she said. "The Cypher is an old stent. Now they've got Liberté. The rest of the world has newer stents but not the U.S. Ask the FDA why we are so slow."
Boston Scientific's Taxus Liberté Atom paclitaxel-eluting coronary stent system was FDA approved in May. It's the second generation of the Taxus Liberté and is a little smaller than most of Boston Scientific's other DES offerings (MDD, May 28, 2009).
Virmani believes this is the first report of stent fracture in a large series assessed at autopsy with a highly sensitive method.
"We've done what we had to do; now we have to look at these next-generation stents. I want the public to be better informed," she said.
Lynn Yoffee, 770-361-4789;