PLATELTE AGGREGATION AFTER VAUVULAR SURGERY EVALUATED BY A LAZER-LITHT SCATTERING METHOD - EFFCTS OF ANTICOAGULANTS

Abstract

Objectives. Effects of anticoagulants in the early phase of platelet aggregation in patients with artificial heart valves are unclear. Newly developed particle-counting methods that employ light scattering (LS) can be used to quantify changes in the number of platelet aggregates of different sizes after application of an aggregating stimulus. Using the LS method, we studied the effects of coumarin and aspirin administration in patients with artificial heart valves. Materials and Methods. Forty-seven patients undergoing valvular surgery were divided into 2 group, 26 patients treated with coumarin alone (group 1), and 21 patients treated with aspirin (81mg/day) and coumarin (group 2). Blood samples were obtained before surgery for control and on day 21 after surgery. Platelet aggregation after stimulation by 2.0 μg/ml collagen was determined; small (9 to 25 μm), medium (25 to 50 μm), and large (50 to 70 μm) aggregates were counted. Results. In group 1, platelet aggregation was not inhibited in both conventional optical density (OD) and LS methods. In group 2, OD methods demonstrated that aggregation was significantly reduced. In LS method, generation of large aggregates after stimulation were significantly decreased in patients treated with coumarin and aspirin than in the control (P 0.034), while, the quantity of the small aggregates was increased (P 0.0005). Conclusion. 1) Coumarin does not suppress platelet function. 2) Although aspirin suppresses platelet function, it does not affect the first phase of aggregation. Platelet dysfunction caused by aspirin is mainly due to an inhibition in the development of small aggregates into larger aggregates.