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Ischemic preconditioning is a process whereby blood supply to the myocardial tissue of the heart is cut off for a short period of time. After the cutting-off process, the blood is allowed to reperfuse the tissues, which means that the blood flow is restored. This is done a number of times. It is thought that the process of ischemic preconditioning might help to prevent ischemic damage of the tissues during myocardial ischemic events, such as heart attack, or myocardial surgery.
Myocardial infarction, or heart attack, is a leading cause of death worldwide. It can be caused by a number of mechanisms, including a buildup of plaque in the vessels, which can eventually cause a blockage of the vessels. This might, in turn, cause some heart tissue to die by cutting off the oxygen supply. This is termed "ischemia" in medicine — the cutting off of blood to an area.
Coronary artery bypass graft (CABG) is a surgical procedure performed on patients who have cardiovascular disease, most commonly after a myocardial infarction. Basically, a piece of blood vessel from another part of the body is attached to the coronary vessel above and below the blocked area, which allows the blood to flow past the blockage. It therefore improves blood flow and oxygen supply to the heart. There is a risk, though, during CABG, of other tissue in the heart becoming ischemic during the procedure.
Experimental medical treatments, such as ischemic preconditioning, are being tested by medical scientists, to minimize this risk. Trials have been performed using specific anesthetics to cut off blood supply for a short period, causing ischemia, then allowing reperfusion. The process is repeated two or more times. The results of these trials have shown that the process might prevent further ischemic damage during surgery by a number of biochemical feedback mechanisms.
There also is the hypothesis in the medical fraternity that ischemic preconditioning might be useful in preventing damage to the heart tissue. This would apply to people who are at high risk for myocardial infarction, such as those with angina. The timing of the ischemic preconditioning, however, will be crucial, if it is proven to be a viable medical intervention.
Ischemic preconditioning might also apply to tissues other than those of the heart, although most work has been done on myocardial tissue. Other tissues that have been investigated are those of the liver, brain and kidney. Ischemic preconditioning of the kidney might help to minimize acute renal failure in people at risk. Studies done in animals have shown a protective effect of ischemic preconditioning.
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