Methods:

This was a prospective, single-center, observational study conducted at the Chonnam National University Hospital in Korea between April 2012 and May 2013. Patients were included in the study if they presented within 3 days of symptom onset, had evidence of acute cerebral ischemia on magnetic resonance imaging, and were not at high risk of cardioembolism. Information regarding stroke risk factors, comorbidities, and stroke severity was prospectively collected. All patients were treated with a 300 mg loading dose of aspirin followed by 100 mg daily. Patients who received anticoagulation were excluded from the study. Platelet reactivity was measured using the VerifyNow test. Initial testing was performed 3 hours after aspirin administration in the emergency department, and a follow-up test was performed on the fifth day of aspirin use. Patients were classified as being aspirin resistant if the aspirin reaction unit (ARU) was >550 IU. The change in ARU between the initial and subsequent testing was calculated, and these values were divided into quartiles (< -70 IU; -70 to -18 IU; -18 to 16 IU; and >16 IU). Early neurological deterioration (END) was the primary clinical outcome of the study and defined as an increase in the National Institutes of Health Stroke Score (NIHSS; a measure of stroke severity) by >1 point. Multivariable logistic regression was used to find factors associated with END. The relationship between the change in ARU and END was also analyzed.