Myocardial infarction (primary prevention with aspirin)

Primary prevention of CVD:

A meta-analysis has added to the evidence that aspirin in the primary prevention setting can reduce the risk of MI (but not stroke); however aspirin use is associated with a significant increased risk of bleeding (1):

• meta-analyses of serious vascular events (myocardial infarction, stroke, or vascular death) and major bleeds in six primary prevention trials (95,000 individuals at low average risk, 660,000 person-years, 3554 serious vascular events)
  • aspirin allocation yielded a 12% proportional reduction in serious vascular events (0.51% aspirin vs 0.57% control per year, p=0.0001)
    • mainly due to a reduction of about a fifth in non-fatal myocardial infarction (0.18%vs 0.23% per year, p<0.0001)
    • net effect on stroke was not significant (0.20%vs 0.21% per year, p=0.4: haemorrhagic stroke 0.04%vs 0.03%, p=0.05; other stroke 0.16%vs 0.18% per year, p=0.08)
    • vascular mortality did not differ significantly (0.19%vs 0.19% per year, p=0.7)
    • the proportional reductions in the aggregate of all serious vascular events seemed similar for men and women
    • adverse effects
      • aspirin allocation increased major gastrointestinal and extracranial bleeds (0.10%vs 0.07% per year, p<0.0001)
      • main risk factors for coronary disease were also risk factors for bleeding
    • in primary prevention without previous disease, aspirin is of uncertain net value as the reduction in occlusive events needs to be weighed against any increase in major bleeds

However if considering primary prevention of CVD and colorectal cancer (CRC):

The USPSTF (US Preventative Services Task force) recommends initiating low dose aspirin use for the primary prevention of CVD and CRC in adults aged 50 to 59 years who have a 10% or greater 10-year CVD risk, are not at increased risk for bleeding, have a life expectancy of at least 10 years, and are willing to take low-dose aspirin daily for at least 10 years (1):

• suggests that decision to initiate low-dose aspirin use for the primary prevention of CVD and CRC in adults aged 60 to 69 years who have a 10% or greater 10-year CVD risk should be an individual one. Persons who are not at increased risk for bleeding, have a life expectancy of at least 10 years, and are willing to take lowdose aspirin daily for at least 10 years are more likely to benefit. Persons who place a higher value on the potential benefits than the potential harms may choose to initiate low-dose aspirin
  
  
• current evidence is insufficient to assess the balance of benefits and harms of initiating aspirin use for the primary prevention of CVD and CRC in adults younger than 50 years
  
  
• current evidence is insufficient to assess the balance of benefits and harms of initiating aspirin use for the primary prevention of CVD and CRC in adults aged 70 years or older

A meta-analysis of use of aspirin in prevention of cancer (3) stated:

• absolute reductions are obviously sex and age dependant, but calculated that if 1,000 people aged 60 took the drug for 10 years, a further decade later (i.e. by the time they were aged 80) there would be:
  • 16 fewer deaths from cancer (NNT 63 over 10 years), 1 less death from heart attack, 2 extra deaths from bleeding (NNH 500 over 10 years)
• analysis of benefits and harms in the general population suggests net benefit for cancer prevention and reduced mortality, for a minimum of 5 years of aspirin prophylaxis between the ages of 50 and 65 with larger benefits for up to 10 years use. In particular, 'there is now overwhelming evidence for a reduction in colorectal cancer incidence and mortality from regular aspirin use..'

Contributor: Kevin Fernando (on behalf of NB Medical) 20/4/16

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. Bibbins-Domingo K; U.S. Preventive Services Task Force. Aspirin Use for the Primary Prevention of Cardiovascular Disease and Colorectal Cancer: U.S. Preventive Services Task Force Recommendation Statement. Ann Intern Med. 2016 Apr 12. doi: 10.7326/M16-0577
3. Torjesen I. Daily aspirin reduces risk of developing and dying from cancer, researchers find. BMJ 2014 Aug 5;349:g5037.