DOCTOR'S VIEW ARCHIVE
Medical Author: Daniel Lee Kulick M.D.
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR
Much has been written and spoken in the media recently about the new "coated" intracoronary stents, and how they are a major advance in the management of coronary artery disease. I would like to present the background on this and discuss the impact and future of these stents.
The nonsurgical treatment of coronary artery disease began with the introduction of balloon angioplasty (PTCA) in the late 1970's. The major drawback of PTCA was recurrence in the first 6-12 months following the procedure, called restenosis (recurrent narrowing), with reported "failure" rates of 30-60%. Many trials were conducted over the next 15 or so years with a multitude of drugs and atherectomy ("roto-rooter") devices, with no appreciable impact on the rate of restenosis. About ten years ago, intracoronary stents became widely available, and reduced the restenosis rate to about 15-30%. The stent is a thin slotted metal tube which is implanted in the coronary artery using a small balloon, in a procedure very similar to standard PTCA. Restenosis after stent implantation occurs because of the formation of soft scar tissue in the center of the stent, which blocks coronary blood flow in a fashion similar to the original blockage that was present before the stent was implanted; the process of restenosis is likely caused by trauma to the inner lining of the wall of the coronary artery when the stent is implanted. Restenosis inside a stent almost invariably occurs in the first 3-12 months after the stent is implanted, and is decidedly unusual after that time period.
While 70-85% of intracoronary stents remain open (patent) for many years, active research has been ongoing to prevent the development of restenosis in the 15-30% of stents doomed to develop restenosis. While restenosis can often be easily treated non surgically with the use of balloons, atherectomy devices, and the use of intracoronary radiation therapy, the prevention of restenosis remains a highly desirable goal. It has been discovered that certain antibiotic and immune-system suppressing agents are able to inhibit the production of scar tissue after stents are implanted in coronary arteries. Recent technology has created a method of impregnating, or "coating" stents with such agents; the most widely studied agent to date has been Rapamycin. Early studies in Europe with Rapamycin-coated stents have resulted in near-zero restenosis rates, which have previously been unprecedented. These stents are now widely available outside the United States.
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In this country, the Food and Drug Administration (FDA) is actively and
rapidly evaluating these stents before approval for use here. The major
questions being evaluated in large numbers of trial patients involve the
long-term safety of these stents, particularly the risk of acute stent closure
due to blood clotting and the potential development of new coronary blockages at
the edge of the stents. If these concerns prove to be very infrequent, which
preliminary data suggests, the stents will hopefully be available in the United
States by the end of this year, or early 2003 at the latest. These stents will
have a higher cost to hospitals and patients than conventional "uncoated"
stents, but will nonetheless be a major advance to the millions of patients in
this country with coronary artery disease, particularly those clinical and
anatomic subsets with a particularly high recurrence risk following coronary
stenting. Look to this column for periodic updates as more information on this
exciting new development becomes available.
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