Response to aspirin and clopidogrel in patients scheduled to undergo cardiovascular surgery

Background: Recent data indicate that among patients undergoing percutaneous coronary intervention low platelet response to aspirin is associated with clopidogrel low response. It is unclear whether these findings extend to other patient populations. We, therefore, aimed to evaluate the relation between response to aspirin and clopidogrel among patients scheduled to undergo cardiac or vascular surgery. Methods: Patients who were scheduled for cardiac or vascular surgery and had taken aspirin 81-325 mg daily for at least a week and clopidogrel 75 mg daily for at least 3 days underwent blood testing for platelet function. One hundred patients were included in the current analysis. Platelet function was evaluated by the modified TEG platelet mapping assay with addition of ADP or arachidonic acid (AA), and by the PFA-100 assay with collagen-epinephrine (CEPI) or collagen-ADP (CADP) cartridges. Low response to aspirin or clopidogrel was defined as inhibition ≤20% for TEG-AA or TEG-ADP, respectively. Results: Thirteen patients (13%) were low responders to aspirin and 34 (34%) were low responders to clopidogrel. Eight patients were low responders to both drugs. There were no differences in clinical characteristics between drug low responders versus sensitive patients. Aspirin low responders had lower TEG-ADP inhibition (19.5 ± 6 vs. 35.8 ± 3%, P = 0.03) and tended to have lower PFA-CADP time (84.7 ± 7 vs. 105.6 ± 5 s, P = 0.1) than aspirin sensitive patients. Clopidogrel low responders had lower TEG-AA inhibition (58 ± 6 vs. 75.1 ± 4%, P = 0.01) and PFA-CEPI time (168 ± 13 vs. 200.4 ± 10 s, P = 0.07) than clopidogrel sensitive patients. Conclusions: In patients scheduled to undergo cardiovascular surgery low response to aspirin is associated with low response to clopidogrel.