Saturday, February 2, 2008

Interventional Cardiology and Clogged Arteries: Stenting

In the beginning, about 30 to 40 percent of patients who underwent interventional procedures could expect their opened arteries to close down again (restenose) in about six months. This was caused either by contraction of the artery (remodeling) or by scar tissue. Interventional cardiologists and scientists sought to find a solution to this problem.

The first major breakthrough in fighting restenosis, or reblockages, was the introduction of stents. Stents are tiny metal mesh tubes which are placed in the artery after the interventional procedure is performed. The stent acts as a scaffold to provide support inside your coronary artery.

"Stents, combined with pharmacologic therapy (see below), are the gold standard for interventional procedures," says Stephen Ellis, M.D., Director of the Cleveland Clinic's Sones Cardiac Catheterization Laboratories. "The earliest stents provided a more predictable short-term and long-term result, and reduced the need for retreatment and restenosis by 10 to 20 percent, depending upon the patient population and type of blockage treated."

Diabetics, pateints with long blockages in small arteries, bypass grafts or at sites of previous stents are at highest risk. Improvement in stent design over the years has allowed interventionalists to use stents in a larger number of cases. In 1994, stents were used in seven percent of patients undergoing angioplasty. Today, they are used in about 90 to 95 percent. Today, stents are available in a variety of lengths and sizes, are more flexible and more readily deliverable.

Bare Metal and Drug Eluting Stents

Stents available before 2003 in United States (bare metal stents) prevented remodeling-related restenosis but actually increased the amount of scar tissue that typically developed after intervention. The net result for most patients was a benefit, but unfortunately 10-40% of patients still developed reblockage within 6-9 months. The healing or scarification process was usually complete by this time, and if restenosis had not yet occurred it was very unlikely to do so later.

To combat scar related restenosis drug eluting stents were developed. Currently these are coated with either sirolimus or paclitaxel, designed to elute or dissolve off the stent over a period of about a month. These medications are also used to treat selected tumors. They reduce the risk of important reblockage down to about 5-25%, but because they interfere with the healing process, the artery itself is somewhat more susceptible to late blood clots compared with bare metal stents.

Even bare metal stents, however, can develop blood clots. Physicians typically prescribe aspirin indefinitely and clopidogrel or plavix for 4-6 weeks to minimize this risk. Nonetheless, about 0.5-1.0% of patients develop blood clots within the first month, and it usually leads to a heart attack. The risk of blood clots with bare metal stents after the first month is very low however.

Drug eluting stents have a similar risk of blood clots for the first month, but appear to have a delayed risk of about 0.3-0 .5% per year for the next several years if aspirin alone is given. For this reason more recently physicians recommend a longer period of plavix, often 1-4 years.

Taking these blood thinners for several years may pose problems for patients that need to undergo surgical procedures. Most surgical procedures can be performed while aspirin is continued, although this increases the risk of bleeding a little bit. Plavix is associated with more risk of surgical bleeding and needs to be stopped for many procedures. However, this poses a risk of blood clot formation on the stent around the time of surgery that may be as high as 3-5%. Consequently, interventionalists much choose carefully between the use of bare metal and drug eluting stents, and if later surgery is required, careful discussion between your cardiologist and surgeon is necessary to minimize the risk.

Recently, new testing has become available to evaluate a patient's response to aspirin and plavix, allowing a more personalized approach to the use of blood thinners associated with stents.

Treatment of Restenosis

For patients whose stents re-block there are several options. If the blockage is quite short balloon angioplasty (sometimes performed with a special cutting tool) is often effective in minimizing long-term risk of reblockage. If the blockage is short to middling in length (5-25 mm or so), placement of a drug eluting stent also often provides a long-term satisfactory solution. If the blockage is quite long, however, often the use of drug eluting stents is associated with reblockage, and bypass surgery is often the best approach. Radiation therapy, or brachytherapy, is no longer used because while the short-term results were good the longer-term results were not better and sometimes worse than balloon angioplasty, both in terms of reblockage and blood clot risk.

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