Aspirin and Antiplatelet Medications (cont.)
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When is aspirin used for preventing and treating heart attacks and strokes?
Aspirin is widely used either alone or in combination with other antiplatelet agents to prevent blood clots from forming in arteries. Aspirin is used specifically in several situations including:
Treatment of heart attacks
In a large multi-center study (Second International Study of Infarct Survival of the ISIS-2 trial) of patients having acute heart attacks, early treatment (within 24 hours of the onset of symptoms) with aspirin (160 mg/d) was found to reduce deaths from the heart attacks by 23%. The improved survival is believed to be due to aspirin's ability to quickly prevent further blood clots and the expansion of existing clots and thus limit the amount of damage to the heart's muscle.
Aspirin is easy to use, safe at the low doses used for its antiplatelet action, and fast acting. Aspirin at moderate doses (160-325 mg/day) produces an antiplatelet effect rapidly (within 30 minutes). The current recommendation is to give aspirin immediately to almost all patients as soon as a heart attack is recognized at a dose of 160-325 mg/d and to continue it for one month. The only reason for not using aspirin is a history of intolerance or allergy to aspirin or evidence obvious active bleeding (such as actively bleeding stomach ulcers).
Performance of vascular procedures
Aspirin is not the only treatment for heart attacks and unstable angina. Sometimes percutaneous transluminal coronary artery angioplasty (PTCA), with or without placement of an arterial stent, is necessary to open narrowed or blocked coronary arteries. In rare instances, PTCA may be technically impossible, or not practical, to do, and coronary artery bypass graft surgery (CABG) becomes necessary to improve the flow of blood to the heart.
Some patients with heart attacks are treated with thrombolytic agents (medications that dissolve clots) to open blocked arteries. It is important to make the distinction that aspirin generally does not open an existing blood clot, but it acts to prevent propagation of the existing clot and the formation of new ones. In all of these instances, there is a risk that blood clots will form again inside the arteries, leading to further heart attacks. In all of these cases, aspirin has been shown to be beneficial in preventing new clots, thus reducing the risk of heart attacks and improving both short and long-term survival.
Prevention of further heart attacks
There are two types of heart attack prevention, primary and secondary. Preventing the first heart attack is called primary prevention. Preventing further heart attacks among patients who already have had a heart attack is called secondary prevention.
Within six years after the first heart attack, 16% of men and 35% of women will have a second heart attack. Long-term, daily aspirin (75-325 mg/d) has been shown to reduce the risk of second heart attacks and improve survival among both men and women. Additionally, long-term secondary prevention with aspirin also has resulted in fewer ischemic (lack of blood flow due to blockage in blood vessels from clot formation) strokes. Therefore, survivors of heart attacks usually take daily low dose (75 mg-160 mg/d) aspirin indefinitely to prevent further heart attacks as well as strokes.
Aspirin taken long-term is an important part but NOT the only measure for preventing heart attacks.
Treatment of exertional and unstable angina
Aspirin is particularly useful in preventing heart attacks and heart attack related deaths in patients with unstable angina. The Canadian Multicenter Trial, and the Montreal Heart Institute study all demonstrated significant reductions (approximately 50%) in the risk of heart attack among patients with unstable angina who are treated with aspirin. A study by the Research on Instability in Coronary Artery Disease Group (RISC) showed a 70% reduction in the risk of death or heart attack in patients with unstable angina treated with aspirin. Aspirin usually is started as soon as the diagnosis of unstable angina is made and then continued indefinitely.
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