A stent is a cylindrical medical device typically made of metal or plastic. Stents have a variety of vascular and nonvascular applications and are used medically to help open tubular body structures that are narrowed or blocked. Since their conception in 1964 by Dr. Charles Dotter, vascular stents have helped revolutionize the minimally invasive, image-guided treatment of arterial and venous disease. Several types of vascular stents are used.
Balloon-Expandable Stents
Balloon-expandable stents are premounted on a balloon catheter and are deployed within a blood vessel by inflating the balloon. This allows for precise stent placement. Once deployed, balloon-expandable stents maintain their shape unless an external force is applied to them. According to Dr. J.F. Dyet's article in the January 2000 issue of "Cardiovascular and Interventional Radiology," these stents can be deformed and should not be placed in locations susceptible to flexion or compression such as the knee joint or the neck. Dr. Dyet also notes that these stents are well suited for the iliac arteries in the pelvis, the renal arteries going to the kidneys and the mesenteric arteries which supply blood to the intestines.
Self-Expanding Stents
Self-expanding stents are compressed onto a catheter and covered by a sheath. They are positioned within a desired blood vessel and unsheathed before assuming their predetermined configuration. These stents commonly require the subsequent use of an angioplasty balloon for full expansion. In contrast to balloon-expandable stents, self-expanding stents are flexible and are capable of returning to their original shape after an external force is applied to them. According to Dr. Dyet, self-expanding stents can be placed in anatomical locations subject to either flexion or compression and these stents are appropriate for the carotid arteries in the neck as well as the vessels delivering blood to the arms and legs.
Stent Grafts
Stent grafts are the union of traditional stents, balloon- or self-expanding, with surgical bypass graft material. These stents utilize a synthetic lining or covering depending on whether the textile membrane is interior or exterior to the stent. According to Dr. Michael Dake's article in the December 1994 issue of "The New England Journal of Medicine," stent graft placement is an accepted treatment option for vascular aneurysms, abnormally dilated blood vessels. He also describes a role for covered stents in treating traumatically injured blood vessels. In the October 2000 issue of "Radiology," Dr. J Lammer writes that the use of stent grafts to dilate narrowed blood vessels may decrease recurrent narrowing following therapy.
Drug-Eluting Stents
In response to a non-physiological stimulus, including stent placement, blood vessels initiate a wound healing process that results in extensive proliferation of their inner lining, known as intimal hyperplasia. This process causes recurrent narrowing, or restenosis. Drug-eluting stents are stents coated with various drugs. In the April 2005 issue of "Circulation," Dr. Sousa states that these stents may decrease intimal hyperplasia and restenosis and may increase the long-term durability of stenting procedures.
References
- "Journal of Vascular and Interventional Radiology"; Physical Properties of Endovascular Stents: An Experimental Comparison; SH Duda, et al; May 2000
- "Cardiovascular and Interventional Radiology"; Mechanical Properties of Metallic Stents: How do These Properties Influence the Choice of Stent for Specific Lesions?; JF Dyet, et al; January 2000
- "Radiology"; J Lammer, et al; Peripheral Arterial Obstruction: Prospective Study of Treatment With a Transluminally Placed Self-Expanding Stent-Graft; October 2000
- "Circulation"; Four Year Angiographic and Intravascular Ultrasound Follow-up of Patients Treated with Sirolimus-Eluting Stents; JE Sousa, et al; April 2005
- "The New England Journal of Medicine"; Transluminal Placement of Endovascular Stent-Grafts for the Treatment of Descending Thoracic Aortic Aneurysms; M Dake, et al; December 1994
