Factors Associated With Aspirin Resistance in Patients Premedicated With Aspirin and Clopidogrel for Endovascular Neurosurgery

OBJECTIVE: Antiplatelet therapy is critical to endovascular neurosurgical procedures. Some patients are aspirin-resistant nonresponders. We reviewed our endovascular neurosurgery patients who were premedicated with aspirin and clopidogrel and identified nonresponders to aspirin. Factors associated with aspirin resistance were determined. METHODS: Consecutive endovascular neurosurgery patients were identified who were treated by the senior author (BLH) from December 2006 to October 2007 and who were premedicated with aspirin (325 mg) and clopidogrel (75 mg) for 7 days before the procedure. We retrospectively reviewed values from the platelet function analyzer-100 test (Dade-Behring, Deerfield, IL) from 1 day before the procedures. The following factors were evaluated for association with aspirin drug resistance: age, sex, body mass index, and smoking history; patients with hypertension, diabetes, coronary artery disease/ peripheral vascular disease, or hypercholesterolemia; disease pathology (aneurysm, intracranial stenosis, or extracranial stenosis); patients taking statins, beta-blockers, angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, or antidepressants; and white blood cell count, hemoglobin, hematocrit, and platelet levels. A stepwise logistic model selection was used to select important factors and their interactions. RESULTS: Eighty-one consecutive patients with the following interventions were included in the study: 35 aneurysm coilings (43%), 21 stent-assisted aneurysm coilings (26%), 13 carotid stent and angioplasties (16%), 7 intracranial stents and angioplasties (9%), and 5 extracranial vertebral artery stents and angioplasties (6%). Seventeen patients (21%) were nonresponders to aspirin. After model selection, the only factor associated with aspirin resistance was not taking an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker (P = 0.0348; odds ratio, 0.214; 95% confidence interval, 0.051-0.896). CONCLUSION: Twenty-one percent of patients premedicated with aspirin and clopidogrel dual therapy for 7 days before endovascular neurosurgical procedures were nonresponders to aspirin. Patients not taking an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker may be at higher risk for aspirin drug resistance.