Sonographic evaluation of platelet aggregate retention in a vortex within a simulated venous sinus

To examine the possible role of venous-valve pockets in enhancing platelet aggregate retention and deposition, in vitro experiments using real-time ultrasonography were performed in a venous-sinus flow model under controlled flow conditions. In each of 10 experiments, adenosine diphosphate (ADP)-induced platelet aggregates in plasma were circulated in both test and control models at upstream shear rates from 60 to 0 sec-1. High-resolution, real-time, B-mode ultrasonography was used to detect and measure the platelet aggregates. Vortex flow was observed in all poststenotic segments, particularly in the sinuses. With reduced shear rates, platelet aggregates increased in size within the vortices and subsequently deposited in the dependent poststenotic tube surface, especially in the sinuses. In conclusion, this study using real-time ultrasonography indicates that the presence of a venous sinus greatly accentuates vortex formation, which, in turn, augments the retention and deposition of platelet aggregates. This relation may provide an explanation for mechanisms that would cause thrombosis to originate in venous-valve pockets.