The results of a recent study published in Neurology showed that patients who developed resistance to aspirin had a significant increase in stroke severity and infarct volume. “Therefore, in patients with new or recurrent ischemic stroke taking aspirin, aspirin resistance assay should be considered before adjusting antiplatelet therapy regimen.” Byung-Chul Lee (Hallym University School of Medicine, South Korea) and co-investigators suggest. They studied 310 patients who were admitted within 48 hours of the onset of acute ischemic stroke and had previously taken aspirin 100 mg/day for at least 7 days. Using the VerifyNow assay, a high residual platelet reactivity (HRPR) of at least 55 was used as a benchmark, and 86 (27.7%) patients were found to be aspirin resistant. These patients had significantly worse stroke severity than those without aspirin resistance, with a mean National Institutes of Health Stroke Scale (NIHSS) score of 6 vs. 3, supporting previous findings. The researchers also used diffusion-weighted imaging (DWI) to clinically assess patients for neurological deficits and found that aspirin-resistant patients had significantly larger infarct volumes, averaging 5.4 cm3 vs 1.7 cm3. After accounting for age, gender, and other variables such as hypertension, antihypertensive medications, stroke type, and delay in symptom onset to hospital visit, aspirin-resistant Patients still had significantly higher NIHSS scores and infarct volumes, with a mean difference of 2.1 points and 2.3 cm3 between the two groups, respectively. Although the study design excluded conclusions regarding a causal relationship between HRPR and stroke severity and infarct volume, the investigators found that the higher quartiles ( 50th, 75th and 90th) had a more pronounced negative effect of aspirin resistance. Thus, “HRPR had a greater negative association with stroke severity in patients with larger thrombi.” They explained. There is also evidence of an association between the preventive effects of aspirin and the underlying mechanisms of stroke. Aspirin resistance was significantly associated with higher NIHSS scores and larger infarct volumes in patients with large-artery atherosclerosis and in patients with other causes or uncertain stroke etiology, but not in patients with cardiogenic stroke or small-vessel occlusion. This suggests that aspirin resistance has a significant effect on stroke severity in patients with atherosclerosis and a relatively small effect in patients with non-atherosclerotic stroke, the team said.