Aspirin Resistance Linked to More Severe Strokes

March 05, 2015

Individuals who exhibit resistance to aspirin may be more likely to have severe strokes than those who respond to the drug, a new study suggests.

Lead author, Mi Sun Oh, MD, Hallym University Sacred Heart Hospital, Seoul, South Korea, commented to Medscape Medical News: "Our results support the need to identify patients with aspirin resistance so an antiplatelet change can be made."

The results will be presented at the upcoming American Academy of Neurology (AAN) 67th Annual Meeting to be held in Washington, DC, in April.

The study involved 310 patients with ischemic stroke or transient ischemic attack within 48 hours of symptom onset and evidence of acute ischemic lesion on diffusion-weighted imaging (DWI), and who were all taking aspirin before the stroke.

Aspirin resistance was measured with the VerifyNow Aspirin assay (Accumetrics) with a cutoff of 550 aspirin reaction units or more designated as aspirin resistance.

Among the 310 patients, 86 (27.7%) were found to be aspirin resistant. Results showed that the median National Institute of Health Stroke Scale (NIHSS) score was higher in this group than in the aspirin-sensitive patients. The volume of the infarction (as measured by DWI) was also higher in the aspirin-resistant patients.

Table. Stroke Size as Related to Aspirin Resistance

Endpoint Aspirin-Resistant Patients Aspirin-Sensitive Patients
Median NIHSS score 6 3
Volume of infarction (mL) 5.4 1.7


In a multivariable median regression analysis, aspirin resistance was significantly associated with higher initial NIHSS score (score difference, 2.06; 95% confidence interval [CI], 0.81 - 3.94; P < .001). In addition, aspirin resistance was a significant predictor of larger DWI infarction volumes (volume difference, 2.70 mL; 95% CI, 0.37 - 4.00; P < .001).

Regarding the mechanism behind the association, Dr Oh explained that antiplatelet agents such as aspirin reduce platelet aggregation, the formation of thrombus, and the size and frequency of thrombotic emboli. "Therefore, the patients with inadequate platelet inhibition have larger size and worse stroke due to larger thrombus and higher rate of thrombotic emboli compared to those without."

Dr Oh added that it is not routine clinical practice to test for aspirin resistance. For patients with aspirin resistance, there are few data from clinical trials on whether an alternative antiplatelet regimen is superior to aspirin for preventing cardiovascular, disease including stroke. A randomized controlled trial looking at this is therefore needed.

"However, in my opinion, the different antiplatelet (such as clopidogrel) could be considered as alternatives to aspirin to prevent next stroke in high-risk patients with aspirin resistance," Dr Oh added.

The study was supported by a grant of the Korea Healthcare Technology R&D project, Ministry of Health and Family Welfare and the Republic of Korea.

To be presented at the American Academy of Neurology (ANA) 67th Annual Meeting, April 18-25, 2015.


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