Reduced antiplatelet activity (low response (LR)/high on-treatment platelet reactivity (HPR)) of aspirin (ALR) or clopidogrel (CLR) is associated with an increased risk of thromboembolic events. The prevalence figures for low-responders reported in the literature vary widely and there have been few investigations in vascular surgery patients to date. The aim of this prospective monocentric study was to increase the evidence base on vascular surgery patients and to detect any changes in the response following vascular surgery procedures.

The activity of aspirin (acetylsalicylic acid, ASA) and clopidogrel is measured by whole blood impedance aggregometry using a multiple electrode aggregometer (Multiplate). The agonists used are arachidonic acid for aspirin and adenosine diphosphate (ADP) for clopidogrel. Vascular patients requiring treatment for peripheral artery disease (PAD) and/or carotid stenosis are included in the study. To identify possible risk factors demographic data, concomitant medication, laboratory parameters, co-morbidities, severity of the condition and the type of procedure performed are documented. In addition, a follow-up aggregometry is performed after completion of the vascular procedure.

Inclusion Criteria:

• Vascular patients requiring treatment for peripheral artery disease (PAD) and/or carotid stenosis are included in the study.

Exclusion Criteria:

• non-adherence to the antiplatelet medication
• abnormal platelet count in patients,
• current gastrointestinal disorders,
• current infections,
• serious concomitant medical conditions (such as recent gastrointestinal bleeding, cancer, severe cardiac or liver disorders)
• known bleeding or coagulation disorders,