Drug-Eluting Stents Break More Often Than Thought

by Brendon Nafziger, DOTmed News Associate Editor | November 13, 2009
Important findings in the
the Journal of the American
College of Cardiology
Drug-eluting stents might break more often than anybody realized, according to a new study in the Nov. 17 issue of the Journal of the American College of Cardiology.

Although the clinically reported rate of fracture of drug-eluting stents is about 1 or 2 percent, researchers at the CV Path Institute in Gaithersburg, MD say the true rate could be much higher.

Doctors at the cardiovascular research non-profit examined X-rays of 177 stents in arteries removed from bodies during autopsy. They found that about 51, or 29 percent, of the stents were broken.
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Of the cracked stents, about 5 percent were associated with clinically significant problems such as blood clotting or re-narrowing of the arteries.

Fracturing was more likely to occur if the stent was long, if stents overlapped (sometimes doctors place one over another to cover a long lesion) or if there was a gap between stents of around 5mm or greater.

Renu Virmani, M.D., lead author of the study and the founder of CV Path, blames much of the breakage on "bad design of the stent."

"If you put long stents in tortuous arteries, you can understand the heart beats and there's stress on those points," she tells DOTmed News. In the study, Cypher stents were the most vulnerable to breaking, with fractures commonly happening on the ring-shaped linkers, the weakest parts of the device, according to Dr. Virmani.

Newer Stents Not Studied

Newer generation stents, such as Boston's PROMUS and Medtronic's ENDEAVOR, weren't included in the study, as Dr. Virmani hasn't seen enough of them in the samples she was sent. Still, she expects them to be tougher, as in animal studies they don't seem to break. Plus, the material used to build most of the new stents has changed from stainless steel to cobalt chromium, which Dr. Virmani says is much stronger.

However, Dr. Virmani acknowledges that her sample isn't completely unbiased. "These are autopsy cases," she says, where oftentimes the physician sending the samples to Dr. Virmani wants to know the cause of mysterious sudden death. "The incidence [of fracture] is not going to be the same." Still, she says, "I do think [stents] fracture more often than is picked up."

Dr. Virmani supports increased use of ultrasound to tell how well stents are deployed, as she says that's really the only way -- pre-autopsy -- to find out how the stent is doing. "That's the only way clinically to find fractures," she says. "It's much harder in X-ray. We could X-ray because we had the arteries in our hands."