Broken heart stents may be more common than thought

* Older, longer, or overlapped stents fracture prone

* Cypher more likely to break than Taxus

By Julie Steenhuysen

CHICAGO, Nov 9 (Reuters) - Heart devices known as drug-eluting stents may be far more prone to breaking than expected and may cause blood clots and scar tissue formation in some patients, U.S. researchers said on Monday.

They studied hearts obtained in autopsies and found 29 percent of drug-releasing heart stents -- tiny wire mesh coils that prop open clogged heart arteries -- had fractures in them.

Older stents, longer stents, and stents that overlapped one another were more likely to fracture, Dr. Renu Virmani of the Cardiovascular Pathology Institute in Maryland and colleagues reported in the Journal of the American College of Cardiology.

They also found the Cypher stent made by Johnson & Johnson (JNJ.N) was more likely to break than the Taxus stent made by Boston Scientific Corp (BSX.N).

Both are older, first-generation, drug-eluting stents -- devices that release drugs over time to prevent scar tissue from forming that could re-clog a treated artery.

They have largely been replaced by newer models, such as Abbott Laboratories (ABT.N) Xience, co-marketed as Promus by Boston Scientific.

Virmani and her colleagues found fractures in 51 of the 177 treated segments they studied. And while simple fractures did not appear to cause side effects in patients, some two-thirds of the broken stents showed signs of scar tissue or blood clots.

Most current estimates suggest that about 1 percent to 5 percent of stents fracture and cause problems for patients. Virmani said the most serious cases occurred at about this rate, but the true number of fractures was likely higher.

For doctors, she said the study suggests where to look if they suspect a stent fracture. Most breaks occurred in the middle, especially in longer stents.

And patients should ask what kind of stent they are getting, whether it is a long segment of artery that is being treated, and whether they are getting an older model.

"Now that we have second-generation, drug-eluting stents, you don't really need to use first generation," she said. (Reporting by Julie Steenhuysen; editing by Leslie Gevirtz)