Dual antiplatelet agent failure: a new syndrome or clinical nonentity?

Aspirin resistance is a well-documented laboratory finding, but the effects of clinical aspirin (ASA) failure on patients with acute coronary syndrome (ACS) have been debated. Likewise, there is recognition of clopidogrel resistance, but the clinical effects of clopidogrel failure are not well understood. We sought to determine the 6-month outcomes of patients who developed an ACS while on ASA or dual antiplatelet agents.

Of all patients admitted to the University of Michigan, Ann Arbor, between 1999 and 2005 with a diagnosis of ACS, 6-month follow-up data were available for 3126. The cohort was divided into 3 groups based on medication history: no prior antiplatelet agent, ASA only, and ASA with clopidogrel (or ticlopidine). Primary end point was the rate of death, myocardial infarction, and stroke, or composite major adverse cardiac events (MACEs) at 6 months.

Aside from a lower rate of myocardial infarction in patients without any prior antiplatelet agent use, there were no significant differences in 6-month stroke, death, or MACE between the 3 medication cohorts. In the propensity-adjusted model, whereas dual antiplatelet status was not an independent predictor of 6-month mortality or MACE, there was a trend toward lower 6-month death rates for patients with prior ASA use (odds ratio 0.72, 95% CI 0.51-1.04, P = .08).

Patients who "fail" antiplatelet therapy do not have overall worse prognosis. Our data do not support ASA or dual antiplatelet agent failure as a distinct clinical entity.