Stents are spring like metallic structures meant to scaffold a blood vessel after angioplasty. They prevent collapse of the vessel and maintain a good lumen for the blood vessel. Coronary stents are small with diameter of only a few millimeters while large stents in big blood vessels like aorta have a diameter of few centimeters.
Coronary stents are made of metals like stainless steel and cobalt-chromium. Bare metal stents have no additional coating while drug eluting stents have a polymer coating containing medications which are released gradually over a period of time. The medication thus eluted prevent in-growth of cells from the blood vessel wall into the stent. This prevents reformation of blocks in the blood vessel and improves long term patency.
What are the potential long term problems after implantation of a coronary stent?
In general coronary stents are well tolerated and quite beneficial in reducing angina (chest pain due to reduced blood supply to the heart muscle). Occasionally some of them may develop restenosis (narrowing) due to in growth of cells. This can be prevented to some extent by using regular medications and implantation of drug eluting stents. Some stents may get clotted (stent thrombosis), mostly when medications to prevent formation clots (blood thinners) are skipped due to some reason. Very rarely some may develop allergy to the metal or coating of the stents.
What are covered stents?
Usual stents have no covering over the metallic struts of the stent. Covered stents have a fabric covering them. Covered stents are useful in stopping blood loss from a vessel which has developed a perforation during angioplasty. Hence it is a life saving device kept in every cardiac catheterization laboratory for use in case of an emergency. Large stents used for treatment of aortic aneurysms are also covered with fabric. Usually they have no covering for a short segment near the tips.