Restenosis
Restenosis literally means the reoccurrence of stenosis, a narrowing of a blood vessel, leading to restricted blood flow. Restenosis usually pertains to an artery or other large blood vessel that has become narrowed, received treatment to clear the blockage and subsequently become renarrowed. This is usually restenosis of an artery, or other blood vessel, or possibly a vessel within an organ. This term is common in vascular surgery, cardiac surgery, and angioplasty, all branches of medicine that frequently treat narrowing of blood vessels. [1]
It can be defined as a reduction in the circumference of the lumen of 50% or more, and had a high incidence rate (25-50%) in patients who had undergone balloon angioplasty, with the majority of patients needing further angioplasty within 6 months. [2]
Causes
Usually surgery to widen or unblock a blood vessel has a long lasting beneficial effect for the patient. However in some cases, the procedure itself can cause further narrowing of the vessel, or restenosis. Angioplasty also called Percutaneous transluminal coronary angioplasty (PTCA)is commonly used to treat blockages of the coronary arteries,or peripheral arteries such as the limbs. The balloon inserted into the narrowing ‘smashes’ the cholesterol plaques (atherosclerosis) against the artery walls, thus widening the size of the lumen and increasing blood flow. However the action does damage to the artery walls, and it responds by using physiological mechanisms to repair the damage. (See physiology below) [3] A stent is a mesh tube-like structure often used in conjunction with angioplasty to permanently hold open an artery, allowing for unrestricted blood flow, or to support a weakness in the artery wall called an aneurysm. The artery can react to the stent, perceive it as a foreign body and respond by mounting an immune system response ( see physiology below) which leads to further narrowing near to or inside the stent.
Physiology
Damage to the blood vessel wall by angioplasty triggers physiological response that can be divided into two stages. The first stage that occurs immediately after tissue trauma, is thrombosis. A blood clot forms at the site of damage and further hinders blood flow. This is accompanied by an inflammatory immune response.
The second stage tends to occur 3–6 months after surgery and is the result of proliferation of cells in the intima, a smooth muscle wall in the vessel. This is also known as Neointimal hyperplasia (NIHA)[4]
Prevention
In the first stage of restenosis, administering anti-platelet drugs (called IIb/IIIa inhibitors) immediately after surgery greatly reduces the chance of a thrombosis occurring.
Drug-eluting stents are now being trialled in Europe and the USA, as well as in Asia-Pacific. These stents are coated with pharmaceuticals that inhibit tissue growth and thus reduce the risk of restenosis from scar-tissue and cell proliferation. [5] There has been some success with these new stents in reducing the occurrence of restenosis, with clinical studies showing an incidence rate of 5% or lower. [6]
Treatment
If restenosis occurs without a stent, it is usually treated with more angioplasty. Once restenosis has occurred and been treated by angioplasty, the chances of restenosis occurring again are increased by a factor of 2.This treatment is also used if restenosis occurs at either end of the stent.
If restenosis occurs within a stent it may be treated with repeated angioplasty and insertion of another stent inside the original; occasionally using a drug-eluted stent.
Alternative treatments include brachytherapy, or intracoronary radiation. The radiation kills cells and inhibits tissue growth (similar to a patient undergoing cancer therapy).
Images of restenosis with bare-metal stents and drug-eluting stents are here .
References
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- Images of restenosis with bare-metal stents and drug-eluting stents are here .
External links
- British Heart Foundation-Angioplasty [1]
- American Heart Association-Stenting [2]pl:Restenoza
