Heart Attack Risk and Medicated Stents

The importance of screening people for coronary artery disease before they develop symptoms is brought to light by the recent condition of ex-president George W. Bush. While he was active and not having cardiac symptoms, a screening stress test as part of his annual physical detected a severe underlying blockage, and he was able to receive a stent and likely prevent a possibly life-threatening heart attack.

Metal stents, devices placed into an artery to keep the vessel open, have been used in lieu of balloon angioplasty to treat patients with coronary artery disease (CAD) for about 15 years, due to their better long-term patency. Nonetheless, with conventional ("bare metal") stents, there may be a disease recurrence rate of at least 20% to 30% due to scar tissue formation within the stent. Much research has been done to try to prevent this scar tissue formation. In the past decade, newer metal stents coated with medication to prevent scar tissue formation have become widely available. These stents have reduced the recurrence ("restenosis") rate of coronary artery disease to well under 10%.

A major concern with use of stents is that the stainless steel they are composed of may promote the formation of blood clots, which may occlude the stent and result in heart attack or even death. When a stent is placed in a coronary artery, the body naturally coats the stent with a protective lining called "endothelium," which serves as a barrier that prevents blood clotting. This process generally is complete within 3 weeks, so patients generally take a regimen of dual antiplatelet therapy (DAPT) for 4 weeks, until the protective lining is in place. This consists of aspirin and a second agent. Traditionally, the second agent was clopidogrel (Plavix), but some patients lack a certain enzyme and are nonresponders to clopidogrel; this can be determined with a simple blood test. In lieu of clopidogrel, two newer agents are often used which don't require enzymatic activation; these are prasugrel (Effient) and ticagrelor (Brilinta).

With the new medicated stents, there has been concern that the medication which prevents scar tissue formation may also delay the formation of the protective endothelial lining as well. For this reason, patients initially receiving medicated stents were advised to take DAPT for 3 to 6 months. In the initial period of medicated stent usage, there were occasional, but infrequent cases when patients would form clots in their stents and have a heart attack soon after stopping the anti-clotting medications. For that reason, cardiologists have generally recommended continuing DAPT for 12 months after receiving a medicated stent. There is also thought that the polymer that binds the drug to the stent may contribute to the risk of stent thrombosis. Research with newer stents containing a biodegradable polymer is ongoing to see if the risk may be minimized.

In recent years, there has been concern that heart attacks or death due to clot formation in medicated stents may develop more than a year after implantation, after discontinuing anti-clotting medication. While this is a significant concern, the number of patients in whom this has occurred is extraordinarily small compared to the large numbers of patients who have received these stents. Furthermore, at this time, there is no conclusive research-based evidence that these new stents do in fact have an increased clotting risk after 1year. It is also important to remember that, since the availability of these new stents, due to the very low disease recurrence risk with the medicated stents, many thousands of patients have been spared the need for coronary artery bypass surgery and its attendant risks.

At the present time, the soundest recommendations for patients who receive medicated stents would be to remain on DAPT for at least 12 months. After 12 months, if the medications are well tolerated, it would probably be prudent to continue with them until ongoing research and scientific investigation can accurately assess if there is in fact an increased risk for blood clots after 1 year, and if taking DAPT over the long term can prevent that. After 12 months, however, if there is a need to go off DAPT for a short time (3 to 7 days) due to bleeding or the need for a surgical procedure, the risk of a blood clot within the stent is generally small, but may be higher in certain situations, depending upon the size, number, or location of the stents. A cardiologist takes all these factors into account and then determines the risk of discontinuing antiplatelet therapy in a given situation.

It is imperative to never stop taking DAPT after receiving a stent without checking with your cardiologist first. If you have received a medicated stent in the past, were on DAPT for the prescribed duration, and then it has been stopped for some time, it is probably not necessary to resume the regimen until more information is available, but you should discuss your concerns about the need for medication with your cardiologist. Hopefully within the immediate future, the true long-term "risk" of the new medicated stents, if any, will be scientifically clarified.