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Ischemia is a condition in which enough oxygen is not delivered by the blood to a major organ, and most often affects the heart or the brain. It occurs when the flow of blood is blocked or when the blood flowing to the organ has an extremely low oxygen content. All of the body's tissues need oxygen to function, so ischemia can result in significant damage or even the shutdown of an organ. Among the causes of ischemia are sickle cell anemia, ventricular tachycardia, the compression of blood vessels, and blood clots. Extremely low blood pressure, congenital heart defects, and the buildup of plaque in the arteries also can cause this condition.
Sickle Cell Anemia
Sickle cell anemia can cause this condition because irregularly shaped or sickle-shaped blood cells can clot more easily, blocking the flow of oxygen-rich blood to the heart, lungs, or brain. In rare cases, a clot can block the passage of oxygen to other organs, such as the liver, creating significant damage. Most people who have sickle cell anemia take anti-clotting medications to prevent ischemia.
Ventricular tachycardia is a series of sudden irregular heartbeats that can cause the heart to function incorrectly or, in the most severe cases, to stop completely. The resulting complications can include ischemia because irregular heart function might also inhibit oxygen flow. In cardiac death as a result of ventricular tachycardia, the heart stops completely, depriving the entire body of oxygen. Although a person can be revived with the use of a defibrillator, lengthy oxygen deprivation can cause damage to major organs.
Compressed Blood Vessels
Growths within the body can cause blood vessels to become compressed. Tumors can press on major arteries, preventing the oxygen-rich blood from flowing freely and resulting in ischemia. Where other factors do not exist, ischemic episodes might indicate the presence of either cancer or large, benign tumors.
Blood clots can be caused by a high platelet count or by surgical procedures, or they can occur in people who are taking an excess of blood clotting agents. In addition, blood clots can form in the legs of people who are inactive for any reason. In very rare cases, blood clots can form in the legs during long airplane flights, causing almost immediate ischemia. Blood clots are often too small to block veins and arteries, but occasionally, a large clot can block blood flow to a major organ, causing great damage.
Low Blood Pressure
A person who is suffering a heart attack usually exhibits extremely low blood pressure, which indicates that the body tissues aren't receiving enough oxyen. Untreated and undiagnosed heart attacks can slow blood flow enough that clots are formed, creating ischemic conditions. People who have had repeated heart attacks may be at greater risk for this condition.
Congenital Heart Defects
Someone who has a congenital heart defect is also at increased risk for ischemia because of clotting, both before and after reparative surgery. Some people who have congenital heart defects are at immediate risk for ischemia at birth. This might be caused by the arteries that are not formed or connected correctly or because one or more arteries are missing.
Buildup of Plaque in the Arteries
Atherosclerosis is the narrowing of arteries caused by the buildup of plaque. This is frequently seen in older people, and it usually can be corrected. This narrowing isn't always detected, however, and ischemia might first present when an artery becomes so completely blocked that blood cannot get to the brain or lungs. Narrow passageways also make it easier for blood to clot and completely block the arteries.
Certain procedures and treatments are used to prevent or correct ischemia. People who are prone to heart attacks or blood clots usually are given appropriate medications to reduce risk of ischemia. Plaque buildup can often be controlled with medication and a diet that reduces cholesterol. Episodes of ventricular tachycardia may be treated with either rhythm-controlling medication or an implanted pacemaker or defibrillator. Surgical correction of congenital defects can create normal blood flow patterns, and any tumors that inhibit blood flow are removed whenever possible.