• Drug-coated stents increase risk of blood clots

    December 2006

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    Boston Scientific Corp. recently released the results of an internal report that showed a slight but statistically significant increased risk of blood clots (also known as late stent thrombosis) in its drug-coated coronary stent Taxus. The preliminary clinical data brings to question the safety and potential complications from its drug-coated stent, as reported by the Wall Street Journal. This is the first acknowledgement of a possible problem with a stent by a manufacturer of stents.

    “Drug-eluting stents dramatically inhibit scar tissue from growing and thus the artery from renarrowing.” 

    Two types of stents: Bare-metal and drug-eluting

    A stent is a tiny, metal mesh tube that is inserted permanently into a previously blocked artery after it has been cleared. The stent enables blood to flow more easily through the artery by holding it open.

    In 1994, the first bare-metal stent was approved for use in the U.S. Bare-metal stents replaced and solved the problems associated with balloon angioplasty but presented a new problem of restenosis or regrowth (and thus reblocking) of the artery wall creating a need for a repeat procedure. In 10 to 20 percent of patients the scar tissue grows around the stent, causing angina (chest pain) and the need for a second procedure.

    In an effort to prevent scar tissue from forming, drug-eluting stents were developed in 2003 and became routinely used in 2004. Drug-eluting stents are coated with a pharmacologic agent that serves to sharply reduce the chance of the artery becoming blocked again through restenosis. Numerous trials have confirmed that drug-eluting stents dramatically inhibit scar tissue from growing and thus the artery from renarrowing.

    With the drug-eluting stent, patients have less recurrent symptoms and only 3 to 5 percent of patients need a second procedure due to restenosis. The drug-eluting stent is extremely successful in reducing restenosis, but thrombosis (formation of blood clots) has become a potential problem.

    Cardiologists prescribe anti-clotting medication that when taken as directed drastically reduces the risk of clots forming. With bare-metal stents a combination of blood thinners was required for only a month, whereas drug-eluting stents require a minimum of three to six months of anti-clotting medication.

    “Despite this increase in blood clots, the company’s analysis did not find an increased rate of heart attacks or death in its drug-coated stent.” 

    Manufacturer research

    According to Boston Scientific, its internal analysis of whether there is an increased risk for blood clots with its drug-eluting stent was finished on June 24. When the results showed an increase, the company contacted the Food and Drug Administration and met with them August 1.

    In a previous report of clinical trials with approximately 3,400 patients, Boston Scientific reported eight thrombosis cases in the drug-coated stent group compared to one case in the bare-metal group during follow-up from six months to three years. That data was further analyzed this summer for the current internal report, with follow-up times up to four years.

    The results show a significant increased risk of thrombosis in drug-coated stents compared to bare-metal stents. Between six months and four years after receiving a drug-coated stent, an added one in every 200 patients (about 0.5% increase) develops a blood clot compared to the bare-metal stent. On Dec. 7, 2006, Boston Scientific presented data to a special FDA panel to show its drug-eluting stent (Taxus) provides substantial benefits to patients with complex coronary artery disease at no higher risk than alternative cardiovascular treatments.

    Two approved stents

    Currently only two drug-eluting stents are used in the U.S., Johnson & Johnson’s Cypher stent and Boston Scientific’s Taxus stent. Boston Scientific was the first company to report an increase in the risk of blood clotting. Its analysis did not find an increased risk of heart attacks or deaths.

    Citing internal studies, Johnson & Johnson claims their stents do not show a significant increase in the risk of late stent thrombosis and that patients with the Cypher stent suffer clotting problems less than patients with Boston Scientific’s stent. Conversely, at the most recent international cardiologist conference (European Society of Cardiology Meeting held in Barcelona in early September) data showed both companies had similar rates of late stent thrombosis.

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Page last updated: 8/7/2015 1:58:01 PM
  • What the news means for you

    Drug-eluting stents have positive impact on treatment

    Steven R. Steinhubl, MD

    Wright, Heather, MDDrug-eluting stents have had a huge positive impact on coronary disease treatment and the numbers of repeat procedures are way down. For the first time, there are new studies that suggest this decrease in repeat procedures may come at the cost of a longer period of risk for a clot to form in the stent. Since drug-coated stents have only recently been available, the length of time a patient is at risk for his or her stent closing abruptly due to blood clots is unknown, but potentially the patient may be a risk for the rest of his or her life.

    “We try to limit drug-eluting stents to patients at high risk for restenosis (renarrowing).” 

    Stent selection

    Of the one million stents put in every year in the U.S., UK cardiologists put in approximately 1,500 to 2,000.

    Because of the high cost of blood thinner medication, we try to limit drug-eluting stents to patients at high risk for restenosis (renarrowing). Patients who have a lot of disease and need a long stent and patients with small vessels in diameter are most likely to have narrowing of the vessel and are best suited for a drug-eluting stent where their chances of restenosis are drastically reduced. Around 80 percent of patients fall into this category.

    However, if the patient has large vessels and not a significant amount of disease, a bare-metal stent is typically used. Additionally if patients are going to undergo a surgery for another reason and will have to stop blood thinners, a bare metal stent will be used because the risk of a clot forming in a drug-coated stent is much higher if the patient has to stop blood thinners early. Approximately 20 percent of patients fall into this later category.

    Importance of blood thinner medication

    The highest risk of blood clots (1.5 %) appears in the first year after implantation. In years two through four after implantation, the risk is reduced to 0.6 percent. This risk is reduced further by the proper application of blood-thinning medications, typically Plavix and aspirin. One of the biggest predictors of a clot forming in the stent is a patient stopping Plavix earlier then directed.

    “Stopping blood thinner medication early increases the risk of a blood clot forming 50 to 80 times.” 

    Stopping blood thinner medication early increases the risk of a blood clot forming 50 to 80 times. The vast majority of patients with stent thrombosis never filled their prescription for Plavix or stopped taking it earlier than recommended. Although incredibly helpful in preventing thrombosis, Plavix is an expensive drug to fill. One should expect to pay around $100 for a month's supply.

    There is a choice of trading off the thrombosis risk associated with drug-coated stents and using a bare-metal stent if the patient does not wish to take Plavix. In the bare-metal stent, restenosis is bad enough to need a second procedure about 10 percent of the time. With drug-eluting stents, a second procedure is required in about 3 percent of cases.

    So, even with a bare-metal stent, 90 percent of patients never experience restenosis. If you have been diagnosed with cardiovascular disease, you should talk with your cardiologist about your options and what will work best for you.

    Follow-up use of medications

    After a drug-coated stent is placed, the majority of patients should expect to be on a blood thinner medication for a minimum of three to six months but typically should be on it for at least a year to lower the risk of thrombosis. Occasionally, if a stent is put in an extraordinarily important place where a blood clot would be life-threatening, or it is a complicated procedure where two stents are put within each other, patients will often stay on aspirin and/or Plavix for the rest of their lives.

    If you have undergone stent surgery within the last year, be sure to talk with your cardiologist before stopping any blood thinner medication.

    Future of drug-eluting stents

    For the biggest benefit to cardiac patients, regrowth around the stent must be more controlled. Future generation stents will more than likely be focused on balancing the amount of regrowth. The goal will be to allow enough growth to cover the stent and thus lessen the chances of a blood clot forming, but not so much growth that the artery becomes blocked.

    Too much regrowth causes recurrent angina but not enough regrowth means the metal the stent is made of is continually exposed to the blood. When the stent is coated with the normal lining of the blood vessel, which happens the vast majority of the time in bare-metal stents, then the stent is less likely to stimulate the blood to form a clot there. In the drug-eluting stents there is a slight increase in blood clots because the drugs on the stent are preventing the regrowth of the vessel wall.

    In addition to more effective future generations of stents, better antiplatelet therapies and blood thinners will also be part of future developments.

    Dr. Steinhubl is a general and interventional cardiologist at the UK Gill Heart Institute and an associate professor of medicine at the UK College of Medicine.

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