U.S. health regulators said they are still investigating a rare but serious problem with Boston Scientific Corp’s new heart stents and required the company to caution doctors about it when the device was approved last month.

The Food and Drug Administration approved the Boston Scientific Promus Element heart stent - a tiny tubular device used to prop open diseased arteries - despite reports about a rare event in which the device becomes deformed after implantation.

While the problem, known as longitudinal stent deformation, occurs with competing stents made by Medtronic Inc and Abbott Laboratories Inc, it appears to happen most often with Boston Scientific’s device, the FDA said.

The reason could be connected to Promus Element’s very thin struts that make the device more flexible and help physicians to implant in narrow or difficult-to-reach vessels. They also make the device more vulnerable to becoming stretched or compressed while being placed in a blood vessel.

“It’s a trade-off,” Ashley Boam, director of the division of Interventional Cardiology Devices Branch at FDA, told Reuters in an interview. “At this time, it still appears this is somewhat of a rare event and ...serious complications in particular are rare.

“It is still something we are looking at carefully,” she said.

When the stent becomes deformed inside the vessel, it creates a clotting risk that could lead to heart attack.

“Our impression at this point is that design does play a role. But the types of lesions the physician is trying to treat also plays a role,” Boam said.

Problems with the Promus Element would be particularly detrimental to Boston Scientific, the biggest manufacturer of stents with more than a third of the $4 billion global market. Not only does it derive a third of its revenue from stent sales, but the Promus Element is the basis for future generations of heart stents.

DESCRIBING THE PROBLEM

The FDA required Boston Scientific to include a section about longitudinal compression on the company’s 20-page label, which includes precautions and instructions for using the device. It describes the problem, discusses situations where it occurs most often, provides guidance and suggests techniques to minimize events.

“Boston Scientific generated the labeling language describing longitudinal stent deformation to provide the user with full information on how to deal with this infrequent phenomenon. The language was then agreed upon with FDA,” Boston Scientific spokeswoman Denise Kaigler said.

The FDA did not require Abbott or Medtronic to include a similar precaution on labels for their stents.

“When there’s a new device like (Promus Element) that’s not a game changer and then you find out there may be issues, you tend not to want to use it,” said Dr. Mark Ricciardi, director of Interventional Cardiology at the University of New Mexico Health Science Center. “Having a warning on the label doesn’t completely say ‘Do not enter,’ but it makes you think.”

The label says, “Although the rate of longitudinal stent deformation is unknown, currently available information suggests that it is a rare adverse event.”

As of October 31, 2011, there were 136 longitudinal stent deformation events per 829,372 units sold worldwide, according to the company.

Dr. Andrew Farb, medical officer, division of International Cardiology Devices Branch of FDA, noted that longitudinal compression seems to be associated most often with calcified lesions, tortuous vessels and older lesions, which are often the most challenging to treat.

These are also the types of cases for which a flexible stent is the best choice, he added.

Concerns about stent deformation were raised in two cardiology journals published in the United States and Europe, and the issue was the subject of a discussion at the Transcatheter Cardiovascular Therapeutics meeting in San Francisco last month.

Dr. Cindy Grines, a cardiologist at the Detroit Medical Center Cardiovascular Institute and editor of the Journal of Interventional Cardiology, said she was unaware of the note on the label.

Grines wrote about the issue in her publication and said she reported it to FDA and to Boston Scientific when she first learned of it.

“It’s good there’s a warning, but it needs to be advertised to the interventional cardiology community. We’re a high volume center and I haven’t heard about it,” she said, adding that having it buried in a label is not useful. “Nobody reads the labels.”

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By Debra Sherman

CHICAGO