The purpose of this study is to investigate the incidence of acetylsalicylic acid resistance (ASA-R) among patients under chronic acetylsalicylic acid(ASA) treatment seen at our outpatient clinic.

Acetylsalicylic acid (ASA) resistance (R) is best defined as an ineffective inhibition of the platelet cyclooxygenase (COX)-1 pathway, and has been reported in 1 to 61 % of patients treated with ASA. Impaired response to ASA has been associated with an increased risk of ischemic events in patients with known coronary artery disease. We sought to investigate the incidence of ASA-R in clinical practice.

All consecutive patients under chronic ASA treatment (100mg/d) seen at our outpatient clinic were systematically included in the registry. All patients were on acetylsalicylic acid for CAD for at least 1 month. Patients were informed of ASA testing at start of consultation in the outpatient clinic. Eligible patients provided written informed consent. Peripheral venous blood samples were analyzed using the whole blood impedance platelet aggregometry Multiplate analyzer. The Multiplate analyzer device allows to measure platelet aggregation by the attachment of platelets to two silver coated copper electrodes leading to a rise of electrical resistance in the sample. The measurements are expressed as arbitrary aggregation units (AU) and the manufacturers defined cutoffs were used: normal values were 76-136 AU, partial antiaggregation was defined as ASA values between 31 and 75 AU and complete antiaggregation was defined as ASA values < 31 AU.

Inclusion Criteria:

• patients under chronic ASA treatment for more then one month

Exclusion Criteria:

• concomitant use of nonsteroidal anti-inflammatory drugs (NSAIDs)
• thrombocytopenia
• thrombocytosis
• age <18 years

All consecutive patients under chronic ASA treatment seen at our outpatient clinic