Aspirin resistance determined from a bed-side test in patients suspected to have acute coronary syndrome portends a worse 6 months outcome

Background: Coronary patients resistant to aspirin may have increased risk for ischemic events. Little data were available for patients presenting acutely with chest pain. Methods and results: We used the VerifyNow Aspirin to determine aspirin responsiveness of 314 patients regularly taking aspirin 75-300 mg daily for >= 4 weeks who presented with suspected acute coronary syndrome in Emergency Department. Aspirin resistance was defined as an aspirin reaction unit (ARU) >= 550, and the clinical team was blinded to the ARU reading. The pre-specified study endpoints were the diagnosis of acute myocardial infarction (AMI) for the index admission and major adverse cardiac events including cardiovascular death or recurrent acute coronary syndrome requiring hospitalization within 6 months. Aspirin resistance was noted in 30 (9.6%) patients. There was no difference in the diagnosis of AMI for the index presentation (3/30, 10% vs. 25/284, 8.8%, P=0.91). Among the 312 hospital survivors, aspirin resistant patients had increased adverse events over 6 months with an overall hazard ratio of 10.0 [95% confidence interval (Cl) 4.6-22.0]. After adjusted for elevated Troponin-T, the only confounder in the model, the hazard ratio was 11.1 (95% CI 4.7-26.0). Results were similar in patients treated only medically without revascularization (adjusted hazard ratio 12.1, 95% CI 4.7-26.4). The increased events were observed both from discharge to 30 days and from 30 days to 6 months. Conclusion: Aspirin resistance occurs in similar to 10% of patients presenting with suspected acute coronary syndrome and is associated with adverse cardiac events.