Background. Low-dose acetylsalicylic acid represents standard antiplatelet therapy in patients after surgical
or endovascular treatment of atherosclerotic carotid artery stenosis. However, almost 8% of these patients
experience restenosis in the same vessel within a year of the procedure, irrespective of the applied technique
or its potential complications. Many authors suggest that complications can be related to a lack of the expected
effect of antiplatelet agents.

Aims: 1) evaluation of platelet activity and incidence of resistance to acetylsalicylic acid (ASA) in thrombosis
prevention after carotid endarterectomy; 2) determination of risk factors for resistance to acetylsalicylic acid
(aspirin resistance).
Material and methods. The study group included 66 patients operated on due to significant stenosis of
carotid arteries (70–99%). The group consisted of 27 women and 39 men, aged 41–80 years.
Patients were administered 75 mg of acetylsalicylic acid daily both before and after operation. Platelet activity
was measured 10 days after operation, using a PFA-100 analyser. The results were classified as normal
response to ASA or resistance to the drug.

Results. Nineteen patients (32%) developed resistance to ASA after operation. Arterial hypertension, treatment
with other non-steroid anti-inflammatory agents, and advanced atherosclerosis of lower limb arteries
were major risk factors of resistance to ASA in multivariate logit regression analysis model.

Conclusions. 1) Incidence of resistance to anti-aggregatory effect of ASA in patients who underwent surgical
interventions for atherosclerotic stenosis of carotid arteries is high, which may mean that no effective antiplatelet
therapy is available for these patients. 2) Advanced atherosclerotic lesions, arterial hypertension, and treatment
with non-steroid anti-inflammatory drugs are risk factors of resistance to ASA. 3) Routine assessment
of resistance to ASA by the bedside may be justified in patients having the above-mentioned risk factors.