Aspirin Protection Reaffirmed For High Risk Myocardial Infarction Or Stroke

Aspirin or other antiplatelet drugs protect patients who are at high risk of serious vascular events and should be considered routinely for all such patients.



This has been shown in a meta-analysis of 287 trials, involving more than 200,000 patients, comparing either an antiplatelet drug with a control or different antiplatelet drugs.



Antiplatelet therapy reduced the risk of any serious vascular event by about one quarter; risk of non-fatal heart attack was reduced by one third, non-fatal stroke by one quarter, and vascular death by one sixth. Low dose aspirin (75-150 mg daily) seemed to be as effective as higher doses for long term use.



The report points out that previous meta-analyses of randomised trials have shown that antiplatelet therapy prevents serious vascular events, arterial occlusion, and venous thromboembolism among a wide range of patients at high risk of occlusive vascular events. The proportional reduction in serious vascular events (non-fatal myocardial infarction, non-fatal stroke, or death from a vascular cause) was about one quarter in a wide range of high risk patients, irrespective of why the risk was high and irrespective of age, sex, blood pressure, or history of diabetes.



“The previous meta-analyses, however, left some important clinical questions unanswered,” the report continues. For instance, although long term antiplatelet therapy was shown to be of substantial benefit after ischaemic stroke, it was not known whether antiplatelet drugs were of net benefit as an immediate treatment in the acute phase of such strokes.



“There was also some uncertainty about whether antiplatelet therapy was of net benefit in patients with chronic conditions such as atrial fibrillation, stable angina, and atherosclerotic peripheral arterial disease that had been less extensively studied. Daily doses of at least 75 mg of aspirin had been shown to be effective in long term use, but theoretical advantages had been proposed for lower doses.”



The researchers point out that a “large amounts of information have become available from trials in patients having coronary artery procedures and in patients with acute stroke, stable angina, atrial fibrillation, peripheral arterial disease, and diabetes mellitus. Consequently, this analysis extends the direct evidence of benefit from antiplatelet therapy to a much wider range of patients at high risk of occlusive vascular disease.



“Antiplatelet therapy reduced the risk of serious vascular events (non-fatal myocardial infarction, non-fatal stroke, or vascular death) by about one quarter, not just among patients with unstable angina, acute myocardial infarction, stroke, or transient ischaemic attacks but also among other patients with coronary or peripheral arterial disease and those at high risk of embolism.



Overall mortality was also significantly reduced in these high risk patients, and, compared with these benefits, the absolute risk of fatal and major non-fatal bleeds was small.”



Results found in this meta-analysis reinforce the value of ensuring that antiplatelet therapy with 75-150 mg aspirin daily (or some other effective antiplatelet regimen) is considered routinely for all such patients at high or intermediate risk of occlusive vascular events (more than about 2 percent a year), irrespective of whether they have already had a major vascular event.



Adding a second antiplatelet drug to aspirin may produce additional benefits in some clinical circumstances, but more research into this strategy is needed.



The report concludes: “An unanswered question, however, is whether it is possible to identify particular groups of apparently healthy people who may be at increased risk of myocardial infarction or stroke and for whom the benefits of daily aspirin outweigh the hazards. This is currently being investigated in an analysis of primary prevention trials.



“For most healthy individuals, however, for whom the risk of a vascular event is likely to be substantially less than 1 percent a year, daily aspirin may well be appropriate.”



This meta-analysis was done by clinicians from a number of British centers and who are members of the Antithrombotic Trialists’ Collaboration, Clinical Trial Service Unit at the Radcliffe Infirmary, Oxford, England.

BMJ 2002; 324:71-86.