Results of the BRAT study--a pilot study investigating the possible significance of ASA nonresponsiveness on the benefits and risks of ASA on thrombosis in patients undergoing coronary artery bypass surgery.

BACKGROUND

Several studies suggest that acetylsalicylic acid (ASA) is less effective in preventing thrombotic events in ASA nonresponder patients. If so, the thrombotic event rate in ASA nonresponders should be higher than in ASA responders.

OBJECTIVE

To conduct a prospective, multicentre observational pilot study to determine the thrombotic event rates in ASA responders and nonresponders.

PATIENTS AND METHODS

Patients undergoing nonurgent coronary artery bypass grafting (CABG) who were prescribed 325 mg ASA/day were recruited. Patients were classified as an ASA responder or nonresponder based on the ASA effect (or lack thereof) on their bleeding times. All thrombotic events that occurred in the two years following CABG were recorded. These data were stored in a blinded fashion until the last patient follow-up, and then adjudicated by a validation committee.

RESULTS

A total of 289 patients recruited at three sites completed the two-year follow-up. Of these patients, 45.3% were classified as ASA responders and 54.7% were classified as ASA nonresponders. Of ASA responders, 6.9% had thrombotic events compared with 9.5% of the ASA nonresponders, but this difference was not significant (P=0.526).

CONCLUSIONS

While ASA responder or nonresponder status did not appear to affect the thrombotic event rate in patients undergoing nonurgent CABG, the possibility that ASA responder or nonresponder status affects the thrombotic event rate in more acutely ill CABG patients cannot be excluded.