A stent is a device used to treat vascular stenosis. Vascular stenosis is a narrowing of the blood vessels usually caused by a build-up of plaque, a condition called atherosclerosis. One method used to treat vascular stenosis is balloon angioplasty. In this procedure, a catheter is inserted into an artery in the leg, arm, or wrist and routed through the body to the blockage site. Imaging technology is used to view the location of the catheter tip during the process. A guidewire is passed through the same artery just past the blockage location. Next, a balloon-tipped catheter is slipped over the guidewire and positioned at the blockage site. The balloon is inflated, generating forces that open the vessel. This may be sufficient to keep the vessel open, but in many cases, the vessel will close again (sometimes completely) if not supported.
A stent is a stiff wire mesh that is designed to hold its shape after being expanded by an angioplasty balloon. Most stents are designed to remain within the body. There are several important factors in the mechanical design of a stent. The stent must be able to be crimped around a deflated angioplasty balloon and have a low profile so that it may be delivered to the blockage site. The stent must also have a high enough radial stiffness to resist the elastic compression of the vessel after being expanded by an angioplasty balloon. It must have radio-opacity, allowing it to be seen in the video monitor during the procedure. In addition, it should not be so opaque that flow within the vessel cannot be observed or the presence of re-stenosis detected. Furthermore, it should have sufficient longitudinal strength to avoid being easily dislodged from its desired location. Mechanical strength and stiffness are achieved through three different methods: change in the metal alloy, change in the strut thickness, and change in the stent architecture (includes shape and interconnections). Stents may also be coated with chemicals that improve healing.
Stents are also used to reduce the chance of aneurysms from rupturing in the brain, aorta, or other blood vessels. An aneurysm results when a portion of the vessel wall weakens and balloons outward. This region of the vessel is thin-walled and susceptible to rupture. The stent is placed in a blood vessel in the area of an aneurysm and diverts much of the flow past the aneurysm down the normal vessel path. This reduces fluid velocity and turbulence in the aneurysm, enabling the blood to clot. This can lead to resorption and shrinkage of the aneurysm wall and its contents.
