Objective

Vein graft failure is the Achilles heel of coronary artery bypass grafting (CABG). Aspirin is the most common drug used to prevent this premature failure. However, significant numbers of patients do not respond to aspirin in the early post-operative period. The aim of this prospective study was to determine the incidence and predictive factors of aspirin resistance following CABG.

Methods

This single centre prospective study included 83 patients who underwent on-pump isolated CABG or combined with valve surgery. Patients with recent coronary stents on dual anti-platelet therapy and patients who were allergic to aspirin were excluded. Patients with significant bleeding post-operatively were also excluded. At least one vein graft was used during CABG. Patients received 75 mg oral aspirin once daily starting on the first post-operative day. Blood samples were collected into hirudin tubes and Multiplate aggregometry test was performed on all patients on day 4. The primary outcome was rate of platelet aggregation on post-operative day 4.

Results

14 out of 83 patients (16.8%) were found to be non-responders to aspirin on day 4 on multiplate test. There was no hospital mortality or myocardial infarctions in the non-responders group. There was early decrease in platelet count from 223.51±63.7 preoperatively to 179.34±47.08 on day 1 after surgery (p=0.01). Thereafter, platelet count increased to 208.42±72.66 on day 4.

Conclusion

16.8% of patients undergoing CABG do not respond to aspirin post-operatively. Routine measurement of aspirin resistance following CABG may change the anti-platelet treatment post-operatively. Further studies are required to determine the optimum anti-platelet therapy following CABG in patients with aspirin resistance.