Failure of aspirin to prevent myocardial infarction and adverse outcome during follow-up - a large series of all-comers.

Background: Aspirin has been used for secondary prevention of myocardial infarction (MI) in individuals with coronary disease. Although supported by several large controlled trials, aspirin prevents only a portion of recurrent events.
Aim and Method: We set out to study the prevalence of long-term aspirin use prior to admission for MI and its significance for medium-term event-free survival; 998 consecutive patients with acute MI admitted to a tertiary center were included in the study.
Results: Nearly half (42.4%) of all patients reported long-term use of low-dose aspirin prior to the index event. Prior aspirin use was associated with a 50% increase in the risk of both the combined end point of recurrent unstable angina, recurrent myocardial infarction, stroke, or death (OR 1.49; 95% CI 1.12-2.00, P=0.006) and mortality (OR 1.50; 95% CI 1.03-2.17, P=0.03) during 10-month follow-up. Prior aspirin use was not associated with an increased frequency of added antithrombotic therapy at discharge.
Conclusions: We have found that prior aspirin use is common in patients hospitalized for acute MI. Individuals already on aspirin had increased risk of recurrent ischemic events and all-cause mortality during the 10-month follow-up after their index MI.