1. Introduction: In the setting of a suspected acute coronary syndrome (ACS), aspirin (ASA) is the primary treatment used for platelet inhibition. However, recent studies have demonstrated that up to 20% of patients do not respond to ASA therapy. The ARTIST trial tested whether treatment of ASA resistance with either higher doses of ASA or additional antiplatelet agents would improve responsiveness to platelet inhibition. Methods: Patients presenting to the emergency department (ED) with a chief complaint of chest pain who were either on outpatient aspirin therapy or who received aspirin in the ED were eligible. A total of 772 patients were enrolled at 5 centers. ASA resistance was tested using the VerifyNow® (Accumetrics) device. Patients who exhibited ASA resistance, defined as aspirin resistance units (ARU) 550, were randomized to receive one of four therapies: additional ASA 325 mg, clopidogrel 300 mg or 600 mg, or standard therapy (no additional ASA or clopidogrel). ARU were measured at baseline, 2 hours, and 6-8 hours post-treatment, and the changes in ARU values for each treatment arm were calculated. Results: Changes in ARU values differed significantly between the four treatment arms (p<0.007), with the greatest reduction in ARU seen in patients who received additional ASA. The mean ARU values in the ASA treatment arm were 631 at baseline, 440 at 2 hours, and 450 at 6-8 hours. There was no significant difference among the four arms with respect to amount of aspirin taken before treatment, the duration of outpatient ASA therapy or baseline ARU. The mean clopidogrel resistance units (PRU) in the group given 300 mg of clopidogrel were 194 at 2 hours and 195 at 6-8 hours. PRU values for the group given 600 mg of clopidogrel 238 at 2 hours and 194 at 6 hours. PRU values for the two groups receiving different doses of clopidogrel were not significantly different. Conclusions: In aspirin resistant patients presenting to the ED with a suspected acute coronary syndrome, additional aspirin appears to be an effective treatment for ASA resistance. Title: Effects of Various Treatments on Aspirin Resistance in Patients Presenting to the Emergency Department with Chest Pain: Preliminary Results of the Aspirin Resistance Testing and Initial Strategy for Treatment (ARTIST) Multicenter Trial Jennifer Beede, Susan R Isakson, Lori B Daniels, William F. Penny, W. Frank Peacock, Donald Moffa Jr., Richard Nowak, Michele Moyer, Alan Wu, Alex Harrison, Karen Herbst, J. Douglas Kirk, Deborah Diercks, Alan S Maisel Aspirin Responder (n=674) Aspirin Resistant (n=89)p-value Age (years)58.2 ± 14.058.5 ± 13.9.845 Sex Male400 (87.1%)59 (12.9%).308 Female 275 (89.6%)32 (10.4%) Race Caucasian238 (91.9%)21 (8.1%).032 African American327 (86.7%)50 (13.3%) Hispanic72 (80.9%)17 (19.1%) Asian22 (95.7%)1 (4.3%) History of CAD no390 (88.4%)51 (11.6%).810 yes 253 (87.8 %)35 (12.2 %) History of CHF no518 (89.2%)63 (10.8%).062 yes 146 (83.9%)28 (16.1%) History of Hypertension no161 (87.0%)24 (13.0%).630 yes 508 (88.3%)67 (11.7%) History of CRI no603 (89.1%)74 (10.9%).012 yes 61 (79.2%)16 (20.8%) Table 1. Patient Characteristics Figure 1. Mean ARU values in the four treatment groups at baseline, 2 hours and 6-8 hours. Figure 2. Mean PRU values at 2 hour and 6-8 hours in the groups receiving 300 mg or 600 mg of clopidogrel.