Stent back from whence it came

Cardiac stents may complicate heart surgery.
But are problems due to improper use or the stent itself?

By Sobia Virk

Heart surgery is risky business. The stakes are high enough without the added worry of equipment failure. So it was no big surprise that the news that some stents may be faulty caused quite a stir. The outcry among cardiologists in the US who experienced problems with the new drug-eluting cardiac stents on the market prompted the US Food and Drug Administration (FDA) to seek a comprehensive report on the matter. But the word on the street is that the problem may be due to human error rather than with the device itself.

Recently, Boston Scientific's Taxus Express 2 stent, and last year, the Cordis Corporation's Cypher stent were deemed problematic by some surgeons. However, the problems are a rare occurrence in the experience of Dr Jean Philippe Pelletier, invasive cardiologist at the McGill University Health Centre and assistant professor of Medicine. "We've had a few cases in which the balloon would stick to the Taxus stent, but no major complications. With some manipulation, the balloon was detached."

Both Health Canada and the FDA have issued formal statements addressing adverse effects associated with use of the Cypher, though recent problems encountered with the Taxus didn't warrant any such action. "We are aware of the problems which have been reported to the FDA, and we've followed up with the company. At this point in time, no further action is anticipated by Health Canada," said Paige Raymond Kovach, Media Relations Officer for Health Canada. Boston Scientific is reportedly making minor changes to the design of the Taxus stent to make it easier to use.

Drug-eluting or coated stents are relatively new medical devices that are used in conjunction with balloons in patients suffering from coronary artery disease. The balloon is inflated and presses the stent, a small wire-mesh tube, against the widened artery. Bare stents have been used since the early 1990s in Canada and coated stents were approved by Health Canada in 2003.

Stenting is a safer alternative to open-heart surgery, but the artery can undergo restenosis due to the formation of scar tissue around the stent. Drug-eluting stents were developed to overcome this difficulty. Boston Scientific produces the Taxus Express 2 stent, which is coated with paclitaxel, while the Cordis Corporation manufactures the Cypher stent, coated with sirolimus. Each drug functions to reduce growth of scar tissue around the stent, which obstructs the artery. Not all patients require coated stents though. "Drug-eluting stents are efficacious in patients that have long lesions or in the case of a small artery, which is when restenosis is likely," said Dr Pelletier.

Dr Madhu K Natarajan, an associate professor at McMaster University and cardiologist at the Hamilton General Hospital, has never had a complication associated with stenting. "In Hamilton, we do approximately 1,800 percutaneous coronary interventions per year. Stents, drug-eluting and bare, are implanted in 95% of cases." Of these implants, coated stents are used in approximately 35-50% of patients, based on funding and Cardiac Care Network guidelines.

Since the approval and usage of the Cypher stent, thrombosis, a rare complication, has been documented in over 290 reports to the FDA. "In the early use of these stents, especially the Cypher stent, there was some concern as to whether there was an increased rate of stent closure, subacute or late thrombosis, a few days or weeks following the procedure, possibly related to the stent characteristics," said Dr Natarajan. "However, one has to remember that in these early experiences these stents may have been placed in more high-risk situations and sometimes for compassionate use in patients who had few other options for revascularization."

Ms Kovach of Health Canada says that the problems encountered by cardiologists are not necessarily due to the stent itself, but to improper usage. "Problems arose from it being used off-label or not as intended. The problem was not with stents but with the practice of medicine," said Ms Kovach.