Coronary stent

A coronary stent is a tube-shaped device placed in the coronary arteries that supply blood to the heart, to keep the arteries open in the treatment of coronary heart disease. It is used in a procedure called percutaneous coronary intervention (PCI). Coronary stents are now used in more than 90% of PCI procedures. Stents reduce angina (chest pain) and have been shown to improve survivability and decrease adverse events in an acute myocardial infarction. A coronary stent is a tube-shaped device placed in the coronary arteries that supply blood to the heart, to keep the arteries open in the treatment of coronary heart disease. It is used in a procedure called percutaneous coronary intervention (PCI). Coronary stents are now used in more than 90% of PCI procedures. Stents reduce angina (chest pain) and have been shown to improve survivability and decrease adverse events in an acute myocardial infarction. Similar stents and procedures are used in non-coronary vessels (e.g., in the legs in peripheral artery disease). Treating a blocked ('stenosed') coronary artery with a stent follows the same steps as other angioplasty procedures with a few important differences. The interventional cardiologist uses angiography to assess the location and estimate the size of the blockage ('lesion') by injecting a contrast medium through the guide catheter and viewing the flow of blood through the downstream coronary arteries. Intravascular ultrasound (IVUS) may be used to assess the lesion's thickness and hardness ('calcification'). The cardiologist uses this information to decide whether to treat the lesion with a stent and if so, what kind and size. Drug-eluting stents are most often sold as a unit, with the stent in its collapsed form attached to the outside of a balloon catheter. Outside the US, physicians may perform 'direct stenting', where the stent is threaded through the lesion and expanded. Common practice in the US is to predilate the blockage before delivering the stent. Predilation is accomplished by threading the lesion with an ordinary balloon catheter and expanding it to the vessel's original diameter. The physician withdraws this catheter and threads the stent on its balloon catheter through the lesion. The physician expands the balloon, which deforms the metal stent to its expanded size. The cardiologist may 'customize' the fit of the stent to match the blood vessel's shape, using IVUS to guide the work. It is critically important that the framework of the stent be in direct contact with the walls of the vessel to minimize potential complications such as blood clot formation. Very long lesions may require more than one stent—the result of this treatment is sometimes referred to as a 'full metal jacket'. The procedure itself is performed in a catheterization clinic ('cath lab'). Barring complications, patients undergoing catheterizations are kept at least overnight for observation. Dealing with lesions near branches in the coronary arteries presents additional challenges and requires additional techniques. Though the chances of having complications from a PCI are small, some serious complications include the development of arrythmias, adverse reactions/effects of the dye used in the procedure, infection, restenosis, clotting, blood vessel damage, and bleeding at catheter insertion site. Coronary artery stents, typically a metal framework, can be placed inside the artery to help keep it open. However, as the stent is a foreign object (not native to the body), it incites an immune response. This may cause scar tissue (cell proliferation) to rapidly grow over the stent. In addition, there is a strong tendency for clots to form at the site where the stent damages the arterial wall, if such damage happens. Since platelets are involved in the clotting process, patients must take dual antiplatelet therapy starting immediately before or after stenting: usually an ADP receptor antagonist (e.g. clopidogrel or ticagrelor) and aspirin for up to one year and aspirin indefinitely. However, in some cases the dual antiplatelet therapy may be insufficient to fully prevent clots that may result in stent thrombosis; these clots and cell proliferation may sometimes cause standard (“bare-metal”) stents to become blocked (restenosis). Drug-eluting stents were developed with the intent of dealing with this problem: by releasing an antiproliferative drug (drugs typically used against cancer or as immunosuppressants), they can help reduce the incidence of 'in-stent restenosis' (re-narrowing). One of the drawbacks of vascular stents is the potential for restenosis via the development of a thick smooth muscle tissue inside the lumen, the so-called neointima. Development of a neointima is variable but can at times be so severe as to re-occlude the vessel lumen (restenosis), especially in the case of smaller-diameter vessels, which often results in reintervention. Consequently, current research focuses on the reduction of neointima after stent placement. Substantial improvements have been made, including the use of more biocompatible materials, anti-inflammatory drug-eluting stents, resorbable stents, and others. Restenosis can be treated with a reintervention using the same method.