Heart Attack Treatment (cont.)
Anti-platelet agents
Anti-platelet agents are medications that prevent blood clots from forming
by inhibiting the aggregation of platelets. Platelets are fragments of cells
that circulate in the blood. Platelets begin the formation of blood clots by
clumping together (a process called aggregation). Platelet clumps are then
strengthened and expanded by the action of clotting factors (coagulants) that
result in the deposition of protein (fibrin) among the platelets. Aggregation of
platelets occurs at the site of any injury or laceration, but it also occurs at
the site of rupture of cholesterol plaques in the walls of coronary arteries.
Formation of clots at the site of an injury or laceration is desirable because
it prevents excessive loss of blood, but formation of clots inside coronary
arteries blocks the arteries and causes heart attacks.
There are three types of anti-platelet agents -- aspirin, thienopyridines, and
the glycoprotein IIb/IIIa inhibitors. These agents differ in their mode of
action, anti-platelet potency, speed of onset of action, and cost. For
more, please read the Anti-Platelet
Medication article.
Aspirin
Aspirin inhibits the activity of the enzyme cyclo-oxygenase inside platelets.
Cyclo-oxygenase is an enzyme whose activity is necessary for the formation of a
chemical, thromboxane A2, that causes platelets to aggregate. Aspirin, by
inhibiting the formation of thromboxane A2, which prevents platelets from aggregating
and thereby prevents the formation of blood clots.
Aspirin alone has its greatest impact on improving survival among patients
with heart attacks. Numerous studies have shown that aspirin reduces mortality
(by 25%) when given to patients with heart attacks. Aspirin is easy to use, safe
at the low doses used for anti-platelet action, fast acting (with an onset of
action within 30 minutes), and cheap. Aspirin is given at a dose of 160 mg to
325 mg immediately to almost all patients as soon as a heart attack is recognized. It
also is continued on a daily basis indefinitely after the heart attack. The only
reason for not using aspirin is a history of intolerance or allergy to aspirin.
Aspirin is taken daily following a heart attack to reduce the risk of another heart
attack. (Preventing further heart attacks is called secondary prevention, while preventing
the first heart attack is called primary prevention). The ideal daily dose
of aspirin for secondary prevention has not been established. Some doctors recommend
160 mg; others recommend 81 mg. The reason for this difference has to
do with aspirin's occasional long-term side effect of bleeding (for example from
stomach ulcers). Even though the risk of major bleeding with long-term, moderate
dose aspirin (325 mg/day) is low (less than 1one percent), this risk can be
lowered slightly by using an even lower dose (160 or 81 mg/day).
Aspirin also benefits patients with forms of coronary heart disease other
than an acute heart attack. Aspirin has been shown to reduce heart attacks and
improve survival in the following patients:
- Aspirin improves survival among patients with unstable
angina. Patients with unstable angina experience chest pains at rest or with
minimal exertion. These patients have critically narrowed coronary arteries
and are at imminent risk of having a heart attacks.
- Aspirin improves survival among patients with stable
exertional angina. (These are patients who experience chest pain only with
exertion.)
- Aspirin prevents formation of blood clots at the site
of the PTCA (see below).
- Aspirin prevents the formation of blood clots that can
occlude surgical bypass grafts. (Occlusion of bypass grafts can lead to heart
attacks.)
- Aspirin in low doses (81 mg/day) has been shown to prevent first heart
attacks (primary prevention)
Next: Thienopyridines »
- ACE Inhibitors - Read about ACE inhibitors like Altace, lisinopril, enalapril, ramparil, Zestril and more. Information includes side effects, drug interactions, and pregnancy safety information.
- Coronary Artery Bypass Graft - Read about heart bypass surgery (coronary artery bypass graft surgery, CABG) including how coronary artery disease is diagnosed, treated, recovery time, risks and complications, and the long term results after CABG.
- Congestive Heart Failure - Read about congestive heart failure symptoms like fatigue, abdomen, leg and ankle swelling, shortness of breath, sleeplessness, increased urination, nausea, abdominal pain, and decreased appetite.
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