Aspirin and postoperative bleeding after coronary artery bypass grafting

Abstract

Objective: To evaluate the relationship between aspirin ingestion and postoperative bleeding complications, and to test the hypothesis that there is a subset of patients who are aspirin hyperresponders with a proclivity toward platelet dysfunction.

Summary background data: Despite numerous retrospective and prospective analyses, it is still controversial as to whether aspirin ingestion before coronary artery bypass grafting (CABG) is associated with significant postoperative bleeding.

Methods: Between January 1995 and December 1999, the records of 2,606 consecutive patients undergoing CABG were reviewed to identify patients with a history of aspirin ingestion up until the time of surgery. Aspirin ingestion was correlated with postoperative blood transfusion using multivariate analysis. In a subset of preoperative aspirin users (n = 40), bleeding times were measured before and after aspirin use. Flow cytometry was performed in another cohort of patients with known heart disease (n = 30) to determine the effect of aspirin on platelet surface receptors.

Results: During the 5-year study period, 63% of the CABG patients were identified as aspirin users. Among these, 23.1% required blood transfusions compared with 19% for the nonusers. Non-red blood cell transfusions were more common in aspirin users, as was reexploration for bleeding. Stratification of these results according to the frequency of aspirin use showed that aspirin is an independent multivariate predictor of postoperative blood transfusion only in high-risk patients. In the prospective studies, aspirin treatment resulted in a significant increase in the template bleeding time, an increase in platelet PAR-1 thrombin receptor activity, and a decrease in the binding of platelets to monocytes.

Conclusions: The findings support the hypothesis that aspirin is associated with a greater likelihood of postoperative bleeding. A platelet function testing algorithm that combines preoperative risk factor assessment, template bleeding times, and flow cytometry may allow the identification of aspirin hyperresponders who are at increased risk for bleeding.

Figure 1. Effect of aspirin (ASA) on template bleeding time in 40 patients. Bleeding time measurements were done before and after a single aspirin dose (325 mg).

Figure 2. Effect of aspirin (ASA) on markers of platelet surface activation in 30 volunteers with known coronary artery disease. The von Willebrand receptor is not included because there was no difference between aspirin users and nonusers and because of differences in units of measurement of this receptor.