Evidence for Selective Degradation of Platelet GP IIb/IIIa Complex after Prolonged in Vitro Ventricular Assist

Abstract

Background

Left ventricular assist devices (VAD) have improved survival in patients with end-stage heart failure. Past studies have shown that interactions between blood and synthetic surfaces promote initial bleeding and later thromboembolism. The exact mechanism of blood activation during VAD circulation remains unclear. The purpose of this study was to test the hypothesis that platelet glycoprotein (GP) IIb/IIIa receptor degradation occurs during clinical use of ventricular assist devices.

Methods

Five in vitro nonpulsatile centrifugal VAD circuits were simulated for 4 days using 450 mL of fresh human whole blood. Temperature, activated clotting time, pH, PCO₂, PO₂, Ca++, and glucose were maintained at physiologic values. Flow was maintained at a constant 2.0 L/min/mβ. We examined whole blood platelet aggregation induced by ristocetin, collagen, and adenosine diphosphate (ATP). We also examined whole blood platelet degranulation induced by collagen and ADP.

Results

Platelet aggregation in response to ristocetin, collagen, and ADP irreversibly and progressively declined with prolonged circulation in the VAD. While ADP-induced aggregation declined within the first hour, ristocetin and collagen-induced aggregation declined after 10 hours. Collagen-induced platelet degranulation decreased similar to aggregation, whereas ADP-induced degranulation continued and was preserved throughout the experiment.

Conclusions

These results suggest prolonged circulation of human blood in a VAD circuit irreversibly impair platelet aggregation. The response of circulating platelets to individual agonists suggests that this platelet degradation is partially receptor specific. In our VAD system, ADP-stimulated platelet aggregation is more rapidly degraded with circulation. These results offer preliminary evidence that circulation of human blood in a VAD circuit leads to early degradation of the platelet GP IIb/IIIa complex. GP IIb/IIIa complex degradation is likely to be the mechanism of early VAD associated bleeding.