NEW YORK (Reuters Health) – Mortality in acute coronary syndromes is no lower among those taking aspirin before the event than in non-aspirin users. This apparent “aspirin paradox” is accounted for by the higher rates of coronary risk factors and overt coronary disease among aspirin users, according to a new study.

The authors explain in the October 15 issue of the Journal of the American College of Cardiology that “some recent studies have suggested that prior aspirin use by those who develop an ACS may actually predispose to worse outcomes than those not previously taking aspirin.” This could be due to aspirin resistance, or it could be that aspirin use is simply a marker of high risk.

To clarify the issue, Dr. Christopher P. Cannon, with the TIMI Study Group, at Brigham and Women’s Hospital in Boston, Massachusetts, and colleagues evaluated 66,443 ACS patients who participated in previous TIMI trials.

The team found that the 17,839 prior aspirin users were older than the non-users by about 3.5 years, and had more risk factors for coronary artery disease such as diabetes (23.3% vs 14.6%, respectively), hypertension (56.8% vs 36.5%), hyperlipidemia (49.9% vs 19.9%), and family history of MI (39.6% vs 30.8%). They also were significantly more likely to have had a prior diagnosis of coronary artery disease (80.0% vs 28.2%), to have had a prior MI (45.6% vs 7.90%) or stroke (3.5% vs 0.8%), and to have undergone a revascularization procedure (34.7% vs 3.3%).

Nonetheless, the ACS in prior aspirin users was less severe than in non-aspirin users. For example, rates of ST-elevation MI were 20.8% and 43.4% in the two groups, respectively.

As for outcomes, after adjustment there was no difference between the prior aspirin and non-aspirin users in total 30-day mortality (odds ratio 1.01) or in later mortality (hazard ratio 1:03), according to the report. “However,” the researchers report, “prior aspirin use was associated with a significantly increased risk of recurrent MI on day 30 and through the last follow-up visit (OR: 1.26; and HR: 1.24).

Summing up, Dr. Cannon and colleagues write: “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.”

Reference:

Prior Aspirin Use and Outcomes in Acute Coronary Syndromes

J Am Coll Cardiol 2010;56:1376-1385.