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Background: Platelet function measured by Aggregometry tests (AT) are commonly used to measure the response to antiplatelets in patients undergoing intracranial and coronary stenting. However, its relevance in carotid and vertebral stents (CVS) is unsettled. We aimed to determine the yield of antiplatelet resistance (AR) in CVS patients, and its relationship with early restenosis and new ischemic lesions on magnetic resonance imaging (MRI).Methods: We studied consecutive patients undergoing CVS. Platelet function was assessed before stenting by means of VerifyNow-assay using Aspirin and P2Y12 cartridges. Antiplatelet reactivity was defined using the cut-off values ARU≥550 as Aspirin resistance (AASR) and PRU≥220 as Clopidogrel resistance (CR). Patients received baseline and 5-day MRI. Periprocedural complications, the new ischemic lesions at 5-day MRI and stent permeability by carotid ultrasound at 24 hours, 5 days and 3 months were analysed.Results: A total of 366 patients were screened. Of those, 246 patients were enrolled and tested for platelet function. A total of 135 patients (54.2%) showed AR, 48 AASR (19.5%) and 112 CR (45.5%). Aspirin dose after the test was increased in 21 patients (45.7%). In 22 patients (20%) with CR the daily dose was increased, in 40 patients (37.7%) an extra-loading dose was administrated and in 9 patients (8.4%) we increased both. At 24 hours, one patient showed restenosis >50% and another an occlusion (0.4 and 0.4% respectively). At 5 days, 8 patients had restenosis <50% (13.1%) and in 43 (17.5%) MRI showed new ischemic lesions. At 3 months 9 patients had stenosis >50% (4.5%) and stenting-related recurrence was observed in 3 (1.4%). A larger size lesions at 5-day MRI (OR 0.143; 95%CI 0.028-0.719) and a multi-territorial ischemic pattern (OR 0.143; 95%CI 0.075-0.893) were associated with lack of response to Clopidogrel therapy. No significant differences in AASR were observed across different groups.Conclusion: The yield of antiplatelet resistance in our series was 54.2%. Clopidogrel resistance was associated with a larger size and a multi-territorial stroke pattern at 5-day MRI. More studies are needed to elucidate the clinical impact of Aggregometry test and management recommendations.