Comparative efficacy of in vitro and in vivo metabolized aspirin in the DeBakey ventricular assist device

Abstract

Ventricular assist devices (VADs) are implanted in patients with end-stage heart failure to provide both short- and long-term hemodynamic support. Unfortunately, bleeding and thromboembolic complications due to the severely disturbed, dynamic flow conditions generated within these devices require complex, long-term antiplatelet and anticoagulant therapy. While several studies have examined the effectiveness of one such agent, aspirin, under flow conditions, data comparing the efficacy of in vitro and in vivo metabolized aspirin is lacking. Two sets of studies were conducted in vitro with purified human platelets circulating for 30 min in a flow loop containing the DeBakey VAD (MicroMed Cardiovascular, Houston, TX, USA): (a) 20 μM aspirin was added exogenously in vitro to platelets isolated from aspirin-free subjects, and (b) platelets were obtained from donors 2 h (n = 14) and 20 h (n = 13) after ingestion of 1,000 mg aspirin. Near real-time platelet activation state (PAS) was measured with a modified prothrombinase-based assay. Platelets exposed to aspirin in vitro and in vivo (metabolized) showed 28.2 and 25.3 % reduction in platelet activation rate, respectively, compared to untreated controls. Our results demonstrate that in vitro treatment with antiplatelet drugs such as aspirin is as effective as in vivo metabolized aspirin in testing the effect of reducing shear-induced platelet activation in the VAD. Using the PAS assay provides a practical in vitro alternative to in vivo testing of antiplatelet efficacy, as well as for testing the thrombogenic performance of devices during their research and development.

Fig. 1

Flow loop with MicroMed DeBakey VAD. Platelets were recirculated through a VAD operating at 9,500 rpm and a cardiac output of 4 L/min for 30 min. Platelet samples were withdrawn every 10 min through a silicone port upstream of the VAD. (Adapted with permission from Girdhar et al. [34])

Fig. 2

Platelet activation post-in vitro ASA treatment. a Evolution of PAS for 20 μM ASA-treated platelets and untreated platelets recirculated for 30 min through the VAD showed a b 28.2 % decrease in the PAR after ASA treatment, determined from the slope of lines fit to PAS values (n = 15, p < 0.05). Error bars represent the SEM of PAS or PAR, respectively

Fig. 3

Platelet activation 2 h post-in vivo ASA treatment. a Evolution of PAS for ASA-treated platelets and untreated platelets recirculated for 30 min through the VAD showed a b 25.3 % decrease in the PAR after ASA treatment, determined from the slope of lines fit to PAS values (n = 14, p < 0.01). Error bars represent the SEM of PAS or PAR, respectively

Fig. 4

Platelet activation 20 h post-in vivo ASA treatment. a Evolution of PAS for ASA-treated platelets and untreated platelets recirculated for 30 min through the VAD showed a b 0.6 % increase in the PAR after ASA treatment, determined from the slope of lines fit to PAS values (n = 13, p > 0. 5). Error bars represent the SEM of PAS or PAR, respectively

Fig. 5

Salicylate concentration (SAL) a 2 h and b 20 h post-in vivo ASA treatment. Blood samples showed a mean increase of 6.70 mg/dL SAL 2 h post-ingestion (n = 14, p < 0.001) and 0.01 mg/dL 20 h after ingestion (n = 13, p > 0.5)