Summary

Platelet hyperreactivity may increase the risk of postoperative VTE in an elderly population, and can be an indication of pharmacologic prophylaxis

Abstract

Introduction

While it is suggested that platelet hyperreactivity plays a role in the arterial
thrombi, its link with venous thromboembolism (VTE) is not well defined. Aggregometry
using low concentrations of agonists is proposed as a reliable method to detect
hyperreactivity. The aim of this study was to examine whether platelet hyperreactivity affects
the development of VTE after total knee arthroplasty (TKA).

Methods

Total 150 elderly patients without VTE history were enrolled. Mechanical
prophylaxis was used for VTE after TKA. We performed platelet aggregation using Chronolog
(Chrono-log Corporation, USA) in the presence of low concentrations of ADP (1.0 µM)
and epinephrine (0.4, 1.0 µM), and measured maximal aggregation (%).

Results

At 0.4 µM epinephrine, 69.3%, 15.3%, 15.3% displayed low (<40%), moderate (40-
60%), and high (>60%) levels of aggregation, respectively. The proportion of high level of
aggregation was 36.7%, 30.7% at 1.0 µM of epinephrine and ADP, respectively. The
incidence of VTE was higher in the moderate/high aggregation group (10/46, 21.7%) than in
the low aggregation group (1/104, 1.0%) at 0.4 µM epinephrine (P<0.0001). In predicting
postoperative VTE, sensitivity, and specificity of =40% aggregation at 0.4 µM epinephrine
were 90.9% and 74.1%. Higher mean platelet volume and lower volume of blood loss were
seen in the high aggregation group than in the low aggregation group.

Conclusion

Aggregation response to 0.4 µM epinephrine is an optimal assay to classify
platelet activity. Platelet hyperreactivity may increase the risk of postoperative VTE in an
elderly population and can be an indication of pharmacologic prophylaxis.
Keywords: Platelets, aggregometry, activity, venous thromboembolism, knee arthroplasty