Aspirin and Antiplatelet Medications (cont.)
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In patients with prolonged chest pain due to unstable angina (a situation in which heart attacks are frequent), percutaneous transluminal coronary artery angioplasty (PTCA) with or without stenting may be necessary to open blocked coronary arteries. Aspirin is often used in combination with another antiplatelet agent, such as eptifibatide (Integrilin), and an anti-coagulant (heparin or low molecular weight heparin) to prevent heart attacks while awaiting the PTCA procedure. Aspirin then is used long-term (either alone or in combination with another antiplatelet agent) to prevent blood clots from forming inside the coronary arteries and stents.
In patients with exertional angina (chest pain brought on by exertion), low dose aspirin (75 mg-325 mg daily) given long-term has been shown to significantly reduce the risk of heart attacks, sudden death, and ischemic strokes.
Treatment of ischemic strokes
Ischemic stroke is a process similar to a heart attack. In general, ischemia means injury to a tissue in the body due to lack of blood flow. Accordingly, an ischemic stroke is injury to the brain tissue due to lack of blood perfusion. This usually happens because of atherosclerosis (narrowing and hardening of the blood vessels) of the arteries in the brain. Heart attack is the ischemia of the heart caused by similar process. Another major process for ischemic stroke may be due to an embolism (a blood clot that dislodges and travels from some other location in the body) to the blood vessels in the brain stopping blood from passing through the blood vessel.
When aspirin at moderate doses (160-350 mg/d) is given to patients as soon as an ischemic stroke is recognized (usually within the first 48 hours of the onset of symptoms), survival is improved, and the risk of additional strokes is reduced. Aspirin is believed to benefit patients having acute ischemic strokes by preventing the propagation (extension or growth) of the blood clots and preventing the complete obstruction of the arteries. However, aspirin is not effective in treating or preventing hemorrhagic strokes. In fact, some studies suggest that long-term aspirin use may increase slightly the risk of developing hemorrhagic strokes.
It is important to recognize that aspirin is not the preferred treatment for ischemic strokes. Thrombolytic medications (medications that dissolve clots) are used early (as soon as an ischemic stroke is recognized) to open blocked cerebral arteries.
The major limitation for using these medications is time. For example, for an ischemic stroke, thrombolytics must be given within the first three hours after the first symptoms of a stroke. Many people with strokes may not recognize the symptoms and may delay medical attention for several hours if not days after the onset of stroke symptoms.
Another limitation in their use is that only certain patients qualify to receive these medications. As a result, for patients in whom thrombolytic medications cannot be used (most often because of underlying conditions that can cause excessive bleeding), doctors may consider using aspirin. Thus, aspirin is often the drug that patients with stroke will receive when they are seen in the emergency room.
Prevention of strokes
Patients with prior strokes and TIAs (mini-strokes) usually have significant atherosclerosis of the carotid and /or the smaller arteries within the brain and are at risk of further strokes. (These patients often have coronary atherosclerosis as well and are at risk for heart attacks.) Long-term low-to-moderate doses of aspirin (50-325 mg/d) have been found to reduce the risk of strokes as well as heart attacks in these patients.
Aspirin is not the only medication to prevent strokes among patients with atherosclerosis. Another anti-platelet agent, clopidogrel (Plavix), also has been used, especially in patients who are intolerant or allergic to aspirin. Aspirin is sometimes combined with a second anti-platelet agent, dipyridamole (Persantine, Aggrenox), to prevent strokes.
Antiplatelet agents are not the only measures that prevent strokes. For example, aspirin alone may not be sufficient to prevent embolic strokes in patients at risk for these strokes, such as in patients with atrial fibrillation. In these patients, warfarin (Coumadin), an oral anti-coagulant that is a stronger anti-clotting medication than aspirin, may be necessary.
In patients with ischemic strokes or TIAs who have advanced atherosclerosis and narrowing of the carotid arteries, carotid endarterectomy (a surgical procedure to widen the narrowed carotid artery, the main blood vessel feeding the brain) or the introduction of stents within the carotid artery may be necessary to prevent strokes.
How effective is aspirin for preventing heart attacks among healthy subjects?
Long-term, low dose aspirin (75-160 mg/d) infrequently causes serious side effects. Therefore, among patients with advanced atherosclerosis (patients who already have heart attacks and strokes, patients with angina or TIAs, patients who need PTCA and coronary artery bypass surgery, and patients with symptoms of peripheral vascular disease) the benefits of low dose aspirin usually outweigh the risks of long-term aspirin (discussed below).
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