Ischemia - Definition
Ischemia originates from the Greek meaning “reduced blood” to any organ. Ischemic strokes occur because a blood clot blocks an artery or vessel in the brain. The most common cause is atherosclerosis, a process in which fatty deposits (plaque) form in the vessel walls of the brain. A stroke sometimes occurs because plaque develops in the carotid artery, the main blood vessel in the neck that supplies oxygen to the brain.
Figure 1. Narrowed vessel Figure 2. a vessel with fatty deposits (plaques) form in the vessel walls.
The symptoms of brain ischemia may be transient, lasting seconds to minutes, or can persist for longer periods of time. Blockage of a blood vessel can cause ischemia, and the brain tissues supplied with oxygen by that vessel may die. This tissue death is called an infarct. Unfortunately, neurologic symptoms do not always accurately reflect the presence or absence of infarction.
Besides lowering stroke risk through lifestyle changes and medication, which can help to reduce blood pressure and cholesterol, surgery to remove plaque and other tissue damage may be beneficial.
Ischemia - Treatment
In a procedure called carotid endarterectomy, surgeons open up the carotid artery in the neck and scrape out plaque. This is sometimes done for an acute stroke, but the procedure has more of a role in preventing recurrent strokes.
In a case where the carotid artery is diseased, one treatment option is stenting. The carotid artery is a vessel that supplies the head and neck with oxygenated blood. Surgeons may open up a clogged carotid artery with a small balloon and insert a narrow support tube called a stent. By keeping the blood vessel open, the stent can prevent a possible stroke in the case of a limited blood flow through a diseased vessel. The device helps prevent stroke in people who have had a TIA (temporary ischemic accident) or who have had a previous stroke, including those who have at least 50 percent blockage of the carotid artery . It may also be used in those patients who have no history of stroke, but who have a carotid artery that is at least 80 percent blocked, and who are not good candidates for surgical alternatives.
There are two main types of drugs approved by the FDA* to prevent a recurrent ischemic stroke: antiplatelet agents and anticoagulants. Antiplatelet drugs (e.g., Plavix®, aspirin), prevent clotting by decreasing the aggregating activity of platelets, blood cells that clump together to help form a blood clot. Anticoagulant drugs (e.g., coumadin, heparin) prevent clot formation by interfering with the several steps involved in the fibrous process of blood clotting. These drugs are often prescribed to prevent recurrent thrombotic strokes.
* The Food and Drug Administration (FDA or USFDA) is an agency of the United States Department of Health and Human Services and is responsible for regulating and supervising the safety of foods, dietary supplements, drugs, vaccines, biological medical products, blood products, medical devices, radiation-emitting devices, veterinary products, and cosmetics
A bypass procedure creates a “bridge” connecting the two strong parts of the artery together, leaving the aneurysm (or diseased weak part) in between. The “bridge” is usually constructed by using a blood vessel graft from another part of your body (usually the lower leg). This blood-vessel graft or “bridge” is the bypass. During the bypass surgery, the flow of blood in the diseased artery may need to be stopped for a short time. This temporary stoppage can increase the risk of reducing vital oxygen concentrations to the part of the brain supplied by the diseased artery (Figure 2). This reduction in oxygen supply is called a “stroke,” which can result in a loss of some brain function. A “stroke” can occur naturally, but can also result from the temporary blockage of an artery during surgery.
The purpose of extracranial-to-intracranial (EC-IC) bypass is to increase blood flow to the brain. During this procedure the superficial temporal artery (STA), or a venous conduit graft, will be connected to a branch of the middle cerebral artery (MCA). The STA-MCA bypass facilitates a relatively low-flow blood supply.
The EC-IC bypass has been available as a potential treatment for stroke for the past 30 years. The first EC-IC bypass was performed in Switzerland in 1967. During the past 30 years, the procedure and its indications have undergone intense research. In 1977, an international study was instituted to assess the safety and efficacy of the procedure. The negative results of that study, published in 1985, had a dramatic effect on the number of bypass procedures performed, and to some degree redirected the thinking of all physicians involved in the treatment of stroke. However, the study was widely criticized on many criteria. The main issue concerned the composition of the group of patients who were treated. The results of this study were not comparable with the outcomes of other similar surgeries that were performed. Most neurologists and neurosurgeons believe there is a subgroup of patients that will benefit from revascularization surgery in the form of a bypass. Nowadays, it is recognized that the STA-MCA bypass likely remains an important technique in the treatment of a small subgroup of patients with cerebral ischemia related to hemodynamic compromise.
ELANA Bypass (for EU and Canada only) :
If your doctor feels that it may be safer to avoid stopping the flow of blood in a diseased artery during surgery or that a bypass that facilitates a relatively high-flow blood supply, he or she may decide to use the ELANA Technique. ELANA makes it possible to create a bypass in the diseased artery without having to stop the flow of blood.