Clinical and Health Affairs
What Physicians Should Know about Coronary Stents
By Charanjit S. Rihal, M.D., M.B.A.
Abstract
Coronary stents are widely used for treating stable angina, unstable angina, and acute myocardial infarction. Stents are highly effective in relieving angina pectoris, reducing myocardial ischemia, and improving quality of life for patients. In the vast majority of cases, stents can be implanted with very low morbidity and mortality. Concerns over the risk of stent thrombosis have drawn appropriate attention to deployment technique, patient-specific risk, and the importance of ensuring compliance with dual anti-platelet therapy. This article describes the types of stents on the market and the benefits associated with each, the type of patients who can benefit from stents, the associated medical therapy needed for their use, as well as recent controversies surrounding the use of stents.
Coronary stents were introduced to clinical practice in the United States in 1995. Stenting quickly became the predominant form of revascularization, overtaking bypass surgery by the end of the 1990s. Coronary stents are now the most commonly implanted medical device in the United States, with more than 1 million being implanted annually. Stents are used to treat the entire spectrum of coronary artery disease including stable angina pectoris, unstable angina, non-ST–
elevation myocardial infarction, and acute ST-elevation myocardial infarction. Coronary stents offer minimally invasive revascularization with very low morbidity and mortality. However, meticulous attention to deployment technique and care following the procedure is needed to ensure optimal results. This article reviews what physicians need to know about stents including the types of stents used, indications and contraindications for their use, associated medical therapy needed for their use, as well as recent controversies surrounding stent implantation.
♦ There are 2 basic types of stents—drug-eluting and bare-metal.
Drug-eluting stents (DES), as the name implies, are coated with special polymers that contain antiproliferative drugs. Two DES are currently available in the United States: the sirolimus-eluting Cypher stent and the paclitaxel-eluting Taxus stent. Others are expected to be on the market soon. The drugs used to coat the stents inhibit the amount of neointimal hyperplasia (restenosis) that occurs within them as part of the arterial healing process. Bare-metal stents (BMS) are metal endovascular scaffolds that contain no polymer or drug.
♦ Coronary stents have made percutaneous revascularization remarkably safe and effective.
The vast majority of coronary lesions can be treated quickly and safely with stents, with the risk of emergency bypass surgery being less than 0.5% and an average hospital stay lasting about 1.5 days with either type of stent.1 The use of DES for percutaneous revascularization, as compared with the use of BMS, has resulted in a markedly lower rate of repeat procedures because of restenosis.2 And randomized clinical trials have shown no difference in rates of death or MI between patients who received DES and BMS.3
Detailed analyses from multiple datasets from around the world including randomized trials and large “all-comer” registries have confirmed the safety and efficacy of DES since a major controversy erupted in 2006, when reports of late thrombosis and deaths following DES implantation were made public. Although rates vary somewhat according to definition of stent thrombosis, the thrombosis rate for patients receiving DES and BMS was less than 1% at 1 year and less than 2% at 4 years.3 Rates of death or myocardial infarction by year 4 were similar for patients in each group, with those rates being between 2% and 3% per year.3
A patient’s risk for developing thrombosis depends on multiple factors including the medical condition of the patient and the number, caliber, and length of stents implanted. Patients with diabetes, chronic kidney disease, and peripheral vascular disease, and those receiving long or multiple stents also have a higher risk of MI or death than other patients who receive stents.
♦ Antiplatelet therapy after stent implantation is critical to ensuring a good outcome.
A number of professional societies, along with the Food and Drug Administration (FDA), have issued statements regarding the use of antiplatelet therapy following stent implantation.4 The current recommendations are 325 mg of enteric-coated or nonenteric-coated aspirin daily for the first 6 months following stent implantation, followed by 81 mg of nonenteric-coated aspirin indefinitely. Clopidogrel (75 mg daily) should be used for a minimum of 30 days for patients who receive bare-metal stents and for 1 year for all patients who receive drug-eluting stents, unless that patient is at high risk for bleeding. After 1 year, there is no definitive data either supporting or refuting the use of clopidogrel. However, certain high-risk patients such as diabetic patients with diffuse disease and patients who have had prior bypass surgery may benefit from longer treatment. The patient’s compliance is a crucial factor in obtaining optimal long-term results, and patients should be advised never to discontinue medications on their own. Patients who are unable to afford the necessary medications may benefit from programs offered by drug manufacturers.
♦ High-risk patients may be candidates for stents.
Concern has been raised about off-label use of DES.5 When stents or any medical device or drug are evaluated for commercial release, the FDA considers data from large randomized trials. These trials generally enroll low-risk patients. However, in clinical practice, stents are frequently implanted in a wide spectrum of patients with varying levels of risk.
Outcomes of such patients have been carefully documented in large registries. Those databanks have shown that patients with clinical risk characteristics such as acute myocardial infarction, diabetes mellitus, chronic kidney disease, and multi-vessel disease do indeed have a higher risk of cardiac events following stent implantation. For these patients, risks are elevated no matter what treatment is chosen. When dealing with such patients, it is important to carefully weigh the risks and benefits of all options including ongoing medical therapy, bypass surgery, and stent implantation, and to involve patients in the discussion before deciding on an approach to treatment.
♦ The best reason to implant a coronary stent is symptom relief.
Stents quickly help patients feel better. Among symptomatic patients with stable angina, stents can improve their quality of life and allow them to participate fully in activities of daily living and exercise without chest pain. There are only a few circumstances, such as a large ischemic burden in an active individual or prior cardiac arrest, in which a stent is indicated for an asymptomatic patient.
♦ There is a place for both percutaneous coronary intervention and bypass surgery in treating patients with multi-vessel disease.
Numerous studies have compared these approaches. A recent meta-analysis based on 23 randomized clinical trials found that long-term survival was equivalent for patients who had PCI or bypass surgery, even among those with diabetes.6 But bypass surgery was associated with more complete angina relief, despite a slight increase in the incidence of stroke.
There are at least 2 factors that should be noted when considering the findings of these studies. Repeat procedures were more frequent after PCI because these trials preceded the advent of drug-eluting stents. They generally did not enroll high-risk patients such as those with left-main disease; for those patients, bypass is still the preferred therapy. The studies do suggest, however, that lower-risk patients with multi-vessel coronary disease may be safely treated percutaneously. Among patients with unstable angina or acute myocardial infarction, the situation is clear: They should be triaged to a medical center with percutaneous coronary intervention capabilities for angiography because revascularization improves outcomes.7,8
♦ Secondary prevention is still critical.
The results of the recently published COURAGE trial, which compared optimal medical therapy to medical therapy plus BMS, demonstrate the importance of medical therapy for all patients with coronary artery disease.9 Although the overall rates of death and MI were no different between the groups, those patients who received stents saw their symptoms of ischemia improve more than those who received only medical therapy. However, the real lesson of the COURAGE trial is that while stents are very effective at opening up an artery 10 mm to 20 mm, coronary artery disease still needs to be tackled with preventive therapies.
Aggressive secondary prevention with lifestyle modification and the appropriate medications is crucial for optimal results. Neither stents nor bypass surgery prevent myocardial infarction when used alone, and antiplatelet therapy, lipid-lowering agents, and, often, beta-blockers and ACE inhibitors are indicated for all patients with coronary disease for long-term prevention.
♦ Stents should be considered when patients who have them need other surgeries.
Noncardiac surgery induces a systemic inflammatory and prothrombotic physiologic state that can predispose a patient to stent thrombosis.10 For that reason, it is recommended that stent patients defer procedures that are truly elective for 1 year following stent placement and seek less invasive alternatives for treating their condition when possible.
If surgery cannot be postponed, operating with the patient on dual or single antiplatelet therapy should be considered. The vast majority of surgeries can be safely performed if the patient is taking aspirin. However, the risk of bleeding needs to be weighed against the risk of a postoperative myocardial infarction caused by stent thrombosis. If the patient is taking clopidogrel, it can be withheld for 3 to 5 days prior to surgery and restarted with a
300 mg loading dose within 24 hours of surgery to minimize the risk of postoperative stent thrombosis. Careful attention to adequate postoperative beta-blockade and analgesia is also important.
Researchers have not yet found a role for preventive therapy with IV or low-molecular–weight heparin. Because stent thromboses are platelet-rich white clots, antiplatelet agents may be more effective.
♦ Coronary stents have evolved and will continue to improve.
The perfect coronary stent has yet to be developed. Such a stent would be easy to implant, have a favorable safety profile, and have no risk of late-stent thrombosis. Researchers are currently developing stents that use more biocompatible polymers or coatings or bioabsorbable polymers; they’re also exploring the possibility of bioabsorbable stents. As the population ages and the number of people with coronary artery disease increases, demand for such products will increase.
Summary
Coronary stents have improved the quality of life for millions of patients and have saved the lives of those presenting with acute coronary syndromes and MI. Stents are remarkably effective for relieving angina pectoris, alleviating myocardial ischemia, and improving overall quality of life for patients—all with a very low risk of procedural morbidity and mortality. Repeat hospitalizations and rates of restenosis have been dramatically reduced with the use of DES.
For coronary patients, every alternative has advantages and disadvantages. Physicians and their patients should fully discuss the risks and benefits of medical therapy, bare-metal stents, drug-eluting stents, and coronary artery bypass surgery in order to decide on a treatment that best suits their circumstances. MM
Charanjit Rihal is director of the cardiac catheterization laboratory at Mayo Clinic.
References
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