Aspirin in myocardial infarction

Therapeutic trials testing the efficacy of aspirin in the management of acute myocardial infarction include the following:

• ISIS-2 trial
• ISIS-3 trial
• GISSI-2 trial

A meta-analysis revealed that (1):

• in secondary prevention trials, aspirin allocation yielded a greater absolute reduction in serious vascular events (6.7%vs 8.2% per year, p<0.0001), with a non-significant increase in haemorrhagic stroke but reductions of about a fifth in total stroke (2.08%vs 2.54% per year, p=0.002) and in coronary events (4.3%vs 5.3% per year, p<0.0001).
• proportional reductions in the aggregate of all serious vascular events seemed similar for men and women

NICE state (2):

• offer aspirin to all people after an MI and continue it indefinitely, unless they are aspirin intolerant or have an indication for anticoagulation (see the section on antiplatelet therapy for people with an ongoing separate indication for anticoagulation)
• offer aspirin to people who have had an MI more than 12 months ago and continue it indefinitely
• continue dual antiplatelet therapy for up to 12 months after an MI unless contraindicated
• for people with aspirin hypersensitivity who have had an MI, clopidogrel monotherapy should be considered as an alternative treatment
• people with a history of dyspepsia should be considered for treatment in line with the NICE guideline on gastro-oesophageal reflux disease and dyspepsia in adults
• after appropriate treatment, people with a history of aspirin-induced ulcer bleeding whose ulcers have healed and who are negative for Helicobacter pylori should be considered for treatment in line with the NICE guideline on gastro-oesophageal reflux disease and dyspepsia in adults
• offer clopidogrel instead of aspirin to people who also have other clinical vascular disease, in line with the NICE technology appraisal guidance on clopidogrel and modified-release dipyridamole for the prevention of occlusive vascular events, and who have:
  • had an MI and stopped dual antiplatelet therapy or
  • had an MI more than 12 months ago
    
    
• antiplatelet therapy for people with an ongoing separate indication for anticoagulation
  
  • for people who have a separate indication for anticoagulation, take into account all of the following when thinking about the duration and type (dual or single) of antiplatelet therapy in the 12 months after an acute coronary syndrome:
    • bleeding risk
    • thromboembolic risk
    • cardiovascular risk
    • person's wishes
      
      
  • be aware that the optimal duration of aspirin therapy has not been established, and that long-term continuation of aspirin, clopidogrel and oral anticoagulation (triple therapy) significantly increases bleeding risk
    
    
  • for people already on anticoagulation who have had PCI, continue anticoagulation and clopidogrel for up to 12 months. If the person is taking a direct oral anticoagulant, adjust the dose according to bleeding risk, thromboembolic risk and cardiovascular risk
    
    
  • for people with a new indication for anticoagulation who have had PCI, offer clopidogrel (to replace prasugrel or ticagrelor) for up to 12 months and an oral anticoagulant licensed for the indication, which best matches the person's:
    • bleeding risk
    • thromboembolic risk
    • cardiovascular risk
    • wishes
      
      
  • for people already on anticoagulation, or those with a new indication, who have not had PCI (medical management, CABG), continue anticoagulation and, unless there is a high risk of bleeding, consider continuing aspirin (or clopidogrel for people with contraindication for aspirin) for up to 12 months
    
    
  • do not routinely offer prasugrel or ticagrelor in combination with an anticoagulant that is needed for an ongoing separate indication for anticoagulation
  • for people with an ongoing indication for anticoagulation 12 months after an MI, take into consideration all of the following when thinking about the need for continuing antiplatelet therapy:
    • indication for anticoagulation
    • bleeding risk
    • thromboembolic risk
    • cardiovascular risk
    • person's wishes

Reference:

1. Antithrombotic Trialists' (ATT) Collaboration, Baigent C, Blackwell L, Collins R, Emberson J, Godwin J, Peto R, Buring J, Hennekens C, Kearney P, Meade T, Patrono C, Roncaglioni MC, Zanchetti A. Lancet. 2009 May 30;373(9678):1849-60
2. NICE (2020). Acute coronary syndromes.