Evaluation of aspirin's effect on platelet function early after coronary artery bypass grafting.

Objective: Aspirin therapy decreases mortality and ischemic complication rates after coronary artery bypass grafting (CABG). However, platelet inhibition after oral aspirin seems to be insufficient in the early postoperative period. There are incomplete data reporting aspirin efficacy early after CABG. The aim of this study was to assess the pharmacologic effect of aspirin on platelets in the first postoperative days using the most specific laboratory tests for the evaluation of aspirin efficacy.

Design: A prospective study.

Setting: A clinical study in one cardiac surgery center and measurements in two pharmacologic institutions.

Participants: Thirty patients.

Interventions: Postoperative aspirin efficacy (200 mg/d) was assessed by the suppression of serum thromboxane B(2) (TxB(2)) and by arachidonic acid-induced aggregometry using the MULTIPLATE analyzer. Samples were collected before surgery and on postoperative days 1-5.

Methods And Main Results: The median baseline value (range) of serum TxB(2) was 1.6 ng/mL (1.4-1.9). The median TxB(2) inhibition >90% (the value required for full platelet inhibition) was not achieved until day 5 (-91%, 0.13 ng/mL [0.08-0.22], p < 0.001) and in only 55% of patients. The median baseline ASPI value was 805 (640-975) aggregation units (AU)*min. A significant decrease in aspirin insufficiency was not seen before postoperative day 5 (390 [243-621], p < 0.003) and only 34% of patients reached an effective platelet inhibition on day 5 (cutoff < 300 AU*min).

Conclusions: The effect of aspirin on inhibition of TxB(2) production and arachidonic acid-induced platelet aggregation is impaired during the first postoperative days after CABG. A more effective antiplatelet strategy presumably could increase early graft patency and improve clinical outcomes after CABG.