Increased platelet aggregability during exercise in patients with previousmyocardial infarction, lack of inhibition by aspirin

The aim of the present study was to investigate the effects of acute exerci se on platelet aggregability, blood coagulation, and fibrinolysis in patien ts with recent myocardial infarction, and to examine these effects in relat ion to two different antithrombotic regimens. Forty patients (mean age 60 y ears) were investigated 3 months after a myocardial infarction, They were r andomized to antithrombotic treatment with either warfarin (INR 2.8-4.2) or aspirin 160 mg daily. They performed a standardized ergometer bicycle exer cise test. Blood was drawn before and after the exercise. The platelet func tion tests included a platelet aggregate ratio (PAR). which, in the presenc e of aggregates, is <1. The coagulation products remained largely unchanged during the exercise, whereas the fibrinolytic activity and the catecholami ne levels increased significantly. At baseline, PAR was lower in the warfar in group than in the aspirin group (0.89 vs. 1.00, p = 0.018). During exerc ise, PAR was significantly reduced in both study groups (0.75 vs. 0.80), in dicating increased platelet aggregability. Beta-thromboglobulin decreased i n both groups. The increased platelet aggregability after exercise despite aspirin is probably due to activation by catecholamines. This implies that aspirin may have a limited antithrombotic effect during physical exercise a nd probably also in other situations with increased catecholamine levels, ( C) 2000 Elsevier Science Ltd, All rights reserved.