Platelet aspirin resistance in ED patients with suspected acute coronary syndrome

Background

Platelet aspirin resistance is reported to be as high as 45%. The prevalence of emergency department (ED) platelet aspirin resistance in suspected acute coronary syndrome (ACS) is not described. Our purpose was to determine the prevalence of platelet aspirin resistance.

Methods

We determined platelet aspirin resistance in a convenience sample of ED suspected ACS patients. Eligible patients had longer than 10 minutes of chest pain or an ischemic equivalent. Two hours after receiving 325 mg of aspirin, blood was assessed for platelet function (Accumetrics, San Diego, CA). Definitions are as follows: aspirin resistance, at least 550 aspirin reaction units; positive troponin T, greater than 0.1 ng/mL; significant coronary lesion, at least 70% stenosis. The composite end point was prospectively defined as a 30-day revisit, positive cardiac catheterization, or hospital length of stay (LOS) longer than 3 days.

Results

Of 200 patients, 50.5% were male, 50.0% were black, troponin T was positive in 7.5%, cardiac catheterization was done in 10.5%, and 33.3% had a significant stenosis. Final diagnoses were noncardiac in 83.4%, stable angina in 8.0%, and unstable angina in 8.5%. Overall, 6.5% were resistant to aspirin; and high-risk patients trended to more aspirin resistance than non–high-risk patients (23.1% [3] vs 9.1% [17]; P value 95% confidence interval [CI], −0.0929 to 0.373). One-month follow-up found ED revisits in 12.5% of aspirin-resistant vs 4.9% of non–aspirin-resistant patients (95% CI, −0.114 to 0.182) and rehospitalization in 12.5% of resistant patients vs 4.3% of nonresistant patients (P value 95% CI, −0.108 to 0.187). Although LOS was similar at index admission, if rehospitalized, LOS was 6.5 for aspirin-resistant patients vs 3.2 days in nonresistant patients (P < .0001).

Conclusion

This first report of platelet aspirin resistance in patients presenting to the ED with suggested ACS finds that it is present in 6.5% of patients.