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Aspirin in cardiovascular disease
1Division of Clinical Pharmacology, Vanderbilt University, Nashville.
Insights
Aspirin primarily works by inhibiting platelet function, reducing thromboxane synthesis. Low doses are effective for secondary prevention of myocardial infarction and stroke, but optimal dosing varies by condition.
Area of Science:
- Cardiovascular Pharmacology
- Thrombosis and Hemostasis
Background:
- Aspirin's antithrombotic effects are mainly due to irreversible platelet cyclo-oxygenase inhibition.
- This blockade reduces platelet thromboxane synthesis, a key factor in thrombosis.
Purpose of the Study:
- To review the efficacy of aspirin in preventing various vaso-occlusive events.
- To analyze aspirin's role in secondary prevention of myocardial infarction, unstable angina, and stroke.
- To evaluate aspirin's effectiveness in preventing graft occlusion and its use in prosthetic devices.
Main Methods:
- Analysis of multiple placebo-controlled trials and studies investigating aspirin's effects on platelet function and clinical outcomes.
- Dose-ranging studies were examined for efficacy in different cardiovascular conditions.
Main Results:
- Aspirin significantly depresses platelet thromboxane formation even at low doses (20mg daily).
- Evidence suggests aspirin is beneficial in secondary prevention of myocardial infarction and unstable angina.
- Aspirin (100-975mg daily) prevents early coronary artery bypass graft occlusion, especially when initiated within 24 hours.
- High-dose aspirin (990-1300mg daily) is effective in preventing stroke and death in patients with transient ischemic attacks.
Conclusions:
- Aspirin demonstrates broad efficacy in preventing thrombotic events across various cardiovascular conditions.
- Optimal aspirin dosage varies, requiring further research for specific patient populations and prosthetic applications.
- While effective, aspirin alone is insufficient for preventing thromboembolic complications in prosthetic heart valves and may increase bleeding risk with anticoagulants.
Abstract:
Although other mechanisms may be contributory, the antithrombotic properties of aspirin derive predominantly from its platelet-inhibitory effects. These are mediated via irreversible acetylation of platelet cyclo-oxygenase with subsequent blockade of platelet thromboxane synthesis. Long term administration of doses of aspirin as low as 20mg daily depresses platelet thromboxane formation by more than 90%; however, higher doses appear to be necessary to prevent thromboxane-dependent platelet activation in vivo. While there is evidence of biochemical selectivity with low doses of aspirin, significant reduction of the platelet-inhibitory eicosenoid, prostacyclin, occurs even at dosages ranging from 20 to 40mg daily. The ability of aspirin to prevent the occurrence or recurrence of vaso-occlusion has been extensively investigated. In the secondary prevention of myocardial infarction 7 placebo-controlled trials involving more than 15,000 patients have been completed. The dose of aspirin varied from 300 to 1500mg daily. Although none of the individual trials produced statistically significant reductions in total or coronary mortality, taken together the results are highly suggestive of a beneficial effect of aspirin. Similarly, 2 recent studies in patients with unstable angina demonstrated a protective effect of aspirin against acute myocardial infarction and death. While each study employed widely different doses of aspirin (324mg and 1250mg daily) similar reductions in mortality were reported. The effects of aspirin on the prevention of coronary artery bypass graft occlusion have been evaluated in 9 trials. Aspirin in doses of 100 to 975mg daily was shown to be of benefit in preventing early (less than 6 months) graft occlusion, particularly when therapy was started within 24 hours of operation. In patients with prosthetic vascular grafts of the lower limbs, aspirin has been shown to reduce platelet deposition, however further controlled trials will be required to establish the patient population most likely to benefit and, as in all these studies, the optimum dose of aspirin to employ. In patients with prosthetic heart valves it is clear that aspirin alone is insufficient to prevent thromboembolic complications and when administered as an adjunct to anticoagulant therapy it is associated with a high incidence of bleeding. In contrast, there is convincing evidence from several studies for the efficacy of aspirin in doses of 990 to 1300mg daily in the prevention of stroke and death in patients with transient ischaemic attacks.(ABSTRACT TRUNCATED AT 400 WORDS)