Strokes Compounded With Aspirin Resistance

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Persons who exhibit a resistance to aspirin may be more likely to have more severe, and larger, strokes than those who still respond to the drug, according to a new study.

“Eventually we may be able to identify people who are likely to be resistant to aspirin and give them higher doses or different drugs to prevent blood clots,” said lead author Mi Sun Oh, MD, of Hallym University College of Medicine in South Korea.

Prior aspirin use has been associated with lower stroke severity and decreased infarction size. However, the effect of aspirin resistance on stroke severity has been inconclusive. Clinicians do not routinely test patients for aspirin resistance.

Dr Oh and colleagues set out to evaluate the effect of aspirin resistance on initial stroke severity and infarct size measured by MRI diffusion weighted imaging (DWI) in 310 patients. “We enrolled patients with at least 7 days of aspirin before symptom onset, evidence of ischemic stroke on DWI, and aspirin resistance checked within 24 hours of hospital admission,” he said. A total of 86 patients (27.7%) were resistant to aspirin.

In a multivariable analysis, aspirin resistance was significantly associated with higher initial NIH Stroke Scale score. Aspirin resistance also was a significant predictor of larger DWI infarction volumes. The infarct size was 2.8 cc in aspirin-resistant patients compared with 1.6 cc for those who responded to aspirin.

In conclusion, Dr Oh said: “Aspirin resistance is independently associated with increased initial stroke severity and stroke volume in acute ischemic patients. However, we need better ways to identify people with aspirin resistance before any changes can be made. For now, people who are taking low-dose aspirin to prevent blood clotting and stroke should continue to do so.”

Antiplatelet agents such as aspirin reduce platelet aggregation, the formation of thrombus, and the size and frequency of thrombotic emboli. When patients do not have adequate platelet inhibition, this may lead to larger and more severe strokes because of larger thrombus and higher rate of thrombotic emboli.

The researchers presented their results at the American Academy of Neurology’s 67th Annual Meeting in Washington, DC, April 18 to 25, 2015.

Abstract title: Aspirin Resistance is Associated with Increased Stroke Severity and Infarction Volume