User:Lihuashu1/Drug-eluting stent

Considerations for Use
It is crucial to identify patients who are good candidates for procedural intervention. Generally, patients without symptoms of coronary blockage or without evidence of ischemia (oxygen deprivation) on labs and imaging are not subjected to stent procedures, as the complications and risks of such a procedure would outweigh any potential benefit.

Procedural intervention, such as angioplasty or stent placement, is reserved for patients with clinical symptoms of coronary artery flow reduction or observable coronary artery obstruction on imaging. This is otherwise known as a myocardial infarction (heart attack). These symptoms can include, but are not limited to:

There are two major classifications of myocardial infarction (MI): ST-elevation MI vs. non-ST elevation. The criteria for diagnosis are beyond the scope of this article, but it is important to note that stenting is considered first-line therapy for patients diagnosed with a STEMI.
 * Severe, pressure-like chest pain unrelieved by rest
 * Shortness of breath, fatigue, lightheadedness
 * Palpitations
 * Atypical symptoms: nausea, vomiting, indigestion, confusion, back pain

Off-label use[edit]
Drug-eluting stents also have been shown to be superior to bare-metal stents in reducing short-term complications of stenting in saphenous vein grafts; however, use in these bypass grafts is an example of "off-label" use of drug-eluting stents. That is, this application has not been sufficiently examined by the Food and Drug Administration for that agency to recommend the use. For "on-label" applications, the FDA "believes that coronary drug-eluting stents remain safe and effective when used for the FDA-approved indications. These devices have significantly reduced the need for a second surgery to treat restenosis for thousands of patients each year."

Some concern has been expressed about the overzealous use of stents in general. Two studies found about half of patients received stents for unapproved reasons, with worse outcomes for the patients in both studies. More recent data suggest off-label use of both bare-metal stents and drug-eluting stents has increased risks. However, drug-eluting stents seemed to have similar or improved rates of death or myocardial infarction compared with bare-metal stents, and consistently reduced the need for target vessel revascularization. Overall, the data support the use of drug-eluting stents for off-label indications.

Contraindications[edit]
The only absolute contraindication to stent placement is significant active bleeding. This is due primarily to the need for in-procedure anticoagulation and dual antiplatelet therapy during the recovery period. Other considerations that could prevent the use of stents include a history of in-stent restenosis, bleeding diathesis (high susceptibility to bleed), complex or unsuitable coronary anatomy, and/or a short life expectancy due to other medical conditions.

Benefits
Drug-eluting stents (DES) have been extensively studied, and are generally superior to bare-metal stents concerning the occurrence of major adverse cardiac events (generally defined as death, myocardial infarction, or the need for a repeat revascularization procedure). In a 2019 meta-analysis comparing new generation DES to BMS, 26,616 patients spanning 20 randomized clinical trials were evaluated for primary outcomes of myocardial infarction and cardiac death. Those who received DES had a significantly reduced risk of myocardial infarction and cardiac mortality at 1 year. The superiority of newer generation polymer stents, particularly the cobalt chromium everolimus-eluting stents have been well-studied.

One of the major benefits of drug-eluting stents (DES) to bare-metal stents (BMS) is the prevention of in-stent restenosis (ISR). Restenosis is a gradual re-narrowing of the stented segment that occurs most commonly between 3-12 months after stent placement. High rates of restenosis associated with BMS prompted the development of DES, which resulted in a reduction of ISR incidence to around 5-10%. Continued development of newer generation DES have resulted in the near-elimination of BMS from clinical practice.

Long term outcomes
Data on long term effects of DES is limited. This is primarily because the technology has only been around for the last two decades, so many studies investigating long-term outcomes have yet to be concluded. However, there are a number of studies investigating intermediate-term outcomes. One particular meta-analysis looked at 52,158 patients across 51 trials. At a median 3.8 years follow up, all DES demonstrated superior efficacy compared to BMS, resulting in lower rates of revascularization procedures. Among DES, newer generation devices had substantially improved safety outcomes, specifically in regards to stent thrombosis, recurrent MIs, or death. In another 2016 trial, 9,013 patients who received either DES or BMS to treat coronary artery disease were followed at 6 years in order to determine differences in rates of all-cause mortality (death from any cause) as well as frequency of repeat revascularization, stent thrombosis, and quality of life measures. At 6 years, there were no significant differences in all-cause mortality or quality of life measures. However, rates of repeat revascularization and stent thrombosis were significantly lower in those who received DES as opposed to BMS.

Risks
Like all invasive medical procedures, stent placement carries certain risks. Risks associated with cardiac catheterization procedures include bleeding, allergic reaction to the X-ray contrast agents used to visualize the coronary arteries, and myocardial infarction. With PCI, the requirement for emergency CABG has markedly decreased since the days of balloon angioplasty, such that in some communities, coronary stenting is permitted in hospitals without on-site cardiac surgery facilities. This remains controversial in the United States because of the rare but unpredictable risk of coronary artery perforation. Rarely, a type of allergic reaction to the drug may occur; episodes of fatality have been reported.

Stent thrombosis[edit]
One of the most feared complications of coronary stenting is stent thrombosis. This occurs when a new clot forms within the stent and occludes blood flow, causing another heart attack. Treatment for stent thrombosis is emergent revascularization; however, this is only achieved in two thirds of patients. Accordingly, stent thrombosis carries a 30-day mortality risk of 10-25%. The mechanisms responsible for clot formation are multifactorial, including patient factors (smoking, diabetes, hematologic disorders, etc.), choice of stent, and post-procedural factors (duration of antiplatelet therapy, adherence to follow-up).

Although drug-eluting stents continue to represent a major medical advance for angioplasty, there is no evidence to suggest reduced frequency of thrombosis with DES compared to older BMS. What is more, while thrombosis occurs immediately (<24 hours) with BMS, DES have been associated with stent thrombosis up to 3 years after implantation, a phenomenon not seen prior. Explanations may lie in the very nature that these new stents are designed to function. A stent represents a foreign object in the body, and placement of a stent will inevitably lead to damage of a blood vessel's lining (endothelium). Drug-eluting stents, by their nature, prevents the formation of a new endothelial layer. Endothelialization is a hallmark of vascular healing and is important for the prevention of thrombus formation. Without proper healing, the risk of clot formation persists for a much longer period of time. Thus, clotting suppressant agents are routinely given during placement, and anti-clotting agents are continued well after implantation. For drug-eluting stents, the time course of complete healing in humans is unknown.

In-stent restenosis
As stated earlier, DES were designed to specifically combat issues of restenosis that occurred with BMS. Though less frequent with drug-eluting stents, restenosis still occur in DES.