Aspirin and Antiplatelet Medications (cont.)
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.
Next: Treatment of exertional and unstable angina »
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