Platelet function plays a major role in the understanding of thromboembolic events in prolonged mechanical support. We studied the platelet activation, platelet aggregation profile, and efficacy of aspirin in patients in whom an external ventricular assist device had been implanted.
Fifteen patients were studied prospectively up to 6 weeks after implantation of the same type of ventricular assist device. Platelet function was studied weekly before daily aspirin administration. Aspirin efficacy was tested ex vivo by measuring platelet aggregation triggered by arachidonic acid. Flow cytometry was used to quantify the spontaneous and induced (adenosine diphosphate stimulation) expression of glycoproteins alphaIIbbeta3, Ibalpha, and CD62P on platelet membranes. The plasma levels of von Willebrand factor (von Willebrand factor activity and von Willebrand factor antigen) and fibrinogen were also determined.
Six of the 15 patients (26%) maintained an arachidonic acid-induced platelet aggregation despite daily aspirin treatment (250 mg). CD62P values remained increased during a 5-week postoperative period. Spontaneous levels of glycoproteins alphaIIbbeta3 and Ibalpha on platelet membranes remained within a normal range with a preserved reactivity. The plasma levels of fibrinogen and von Willebrand factor remained increased during the entire study period.
In patients with an implanted external ventricular assist device, the platelet activation profile displays a persistent activation with a preserved reactivity associated with a persistent high inflammatory state and endothelial activation.