The purpose of this study was to determine whether patients taking aspirin before an acute coronary syndrome (ACS) are at higher risk of recurrent events or mortality.

Controversy exists whether prior aspirin use is an independent predictor of worse outcomes in patients who experience an ACS.

We evaluated 66,443 ACS patients from a merged database of previous Thrombolysis in Myocardial Infarction trials. We evaluated the differences in ACS type, total mortality, and the composite end point of death, myocardial infarction (MI), recurrent ischemia, or stroke between prior aspirin and nonprior aspirin users. We used multivariate analysis to control for differences in baseline characteristics.

Prior aspirin users (n = 17,839) were older (63 years vs. 59 years) and had more coronary risk factors and evidence of coronary artery disease (MI, angina, prior intervention) than nonprior aspirin users (n = 48,604) (all p < 0.0001). Prior aspirin use was associated with less severe types of ACS at presentation (e.g., unstable angina > non–ST-segment elevation MI > ST-segment elevation MI) than their nonaspirin user counterparts (p < 0.0001). After multivariate analysis, there was no difference in total mortality between prior aspirin users and nonaspirin users at day 30 (odds ratio [OR]: 1.01; 95% confidence interval [CI]: 0.90 to 1.13) or by the last follow-up visit (mean 328 days) (hazard ratio: 1.03; 95% CI: 0.95 to 1.11). Prior aspirin use was modestly associated with recurrent MI (OR: 1.26; 95% CI: 1.12 to 1.43) and the composite end point (OR: 1.16; 95% CI: 1.08 to 1.24).

Prior aspirin use was associated with more comorbidities and coronary disease and a higher risk of recurrent MI, but not mortality. As such, it should best be considered a marker of a patient population at high risk for recurrent adverse events after ACS.