This prospective, multicenter study assessed aspirin-HTPR status and its relationship with micro-emboli signals (MES) in asymptomatic versus symptomatic ≥50-99% carotid stenosis patients on aspirin monotherapy, aspirin-dipyridamole or aspirin-clopidogrel combination therapy.

Assessment of ‘high on-treatment platelet reactivity’ (HTPR) status in carotid stenosis patients on antiplatelet therapy has the potential to enhance our understanding of the biological basis of first or recurrent vascular events in this patient population. 

Platelet function/reactivity was assessed under ‘moderately high shear stress’ with PFA-100® collagen-epinephrine cartridges, and ‘low shear stress’ with Verify Now® Aspirin and Multiplate® Aspirin assays. Bilateral 1-hour transcranial Doppler ultrasound (TCD) monitoring of the middle cerebral arteries classified patients as MES+ve or MES-ve.

Data from 31 asymptomatic patients were compared with 42 symptomatic patients in the ‘early phase’ (≤4 weeks) and 36 of these patients in the ‘late phase’ (≥3 months) after TIA/ischemic stroke. Median daily aspirin doses were higher in early symptomatic (225mg; P<0.001) but not late symptomatic (75mg; P=0.62) vs. asymptomatic patients (75mg). There was a lower prevalence of aspirin-HTPR in early symptomatic (28.6%; P=0.028) but not late symptomatic (38.9%; P=0.22) compared with asymptomatic patients (56.7%) on the PFA-100®, but differences between groups on the Verify Now® or Multiplate® were not significant (P≤0.53). The proportion of early symptomatic patients with aspirin-HTPR was higher on PFA-100® (28.6%) in comparison with Verify Now® (9.5%; P=0.049) but not in comparison with Multiplate® assays (11.9%, P=0.10). There were no differences in aspirin-HTPR status between early or late symptomatic vs. asymptomatic MES+ve or MES-ve subgroups.

Recently symptomatic moderate-severe carotid stenosis patients had a lower prevalence of aspirin-HTPR than their asymptomatic counterparts on the PFA-100, most likely related to higher aspirin doses in early symptomatic patients. The prevalence of ex vivo antiplatelet-HTPR was positively influenced by higher shear stress rates, but was not associated with MES status.