Objective   To observe the change of the platelet aggregation in early stage of patients after mitral valve replacement.    Methods   Ninety patients (male 39

female 51

with an average age of 26.0±8.1) who underwent cardiac surgery with cardiopulmonary bypass (CPB) from September to December 2009 in our department were divided into 3 groups

congenital heart disease (n=30)

mitral valve replacement with sinus rhythm (n=30)

and mitral valve replacement with atrial fibrillation (n=30). All the prostheses were bileaflet mechanical valves. Blood was sampled at the following time points: on the day before surgery

on the 2nd

4th

6th postoperative day and on the day after 1 month. Platelet aggregation was measured with stimulation by adenosine diphosphate (ADP

5 and 10  μmol/L) and collagen (2 μg/ml).    Results   Platelet aggregation in congenital heart disease group showed no statistically significant difference with that before operation (P0.05). Platelet aggregation was decreased on the 2nd postoperative day and significantly increased on the 4th postoperative day (P0.05)

and the result of ADP (5 and 10  μmol/L) and collagen (2 μg/ml) was (14.56±2.32)

(17.86±2.43) and (21.60±2.60) Ω in the patients with atrial fibrillation. Platelet aggregation in the patients with atrial fibrillation was higher than those in the congenital heart disease group and mitral valve replacement with sinus rhythm group on the day before surgery and on the 4th postoperative day (P0.05).    Conclusion   Platelet aggregation shows significant change in mitral valve replacement during postoperative period

especially within 1 week. We need to pay more attention to these patients because of high risk of thromboembolism.