Platelet activation following rotary pump speed increase

Axial flow ventricular assist devices represent the next generation of heart assist devices. Blood damage may result from the high shear field produced by these devices. Blood damage has previously been quantified in terms of hemolysis. Shear induced platelet activation remains a concern. This phenomenon was assessed using several flow cytometric assays we have developed to the quantify in vivo circulating activated platelets (ACT-PLT), circulating platelet microaggregates (AGG-PLT), platelet consumption and platelet life span. The assays were used to measure platelet activation before, during, and after a step increase in the pump revolutions per minute (RPMs) in three calves implanted with the UOP/Nimbus axial flow ventricular assist device. A marked increase in ACT-PLTs and AGG-PLTs immediately followed the RPM increase, with recovery in these parameters over time. Platelet life span decreased from 102 ± 10 hours before the RPM change to 83 ± 14 hours (p<0.05) after the step increase. This corresponded to a 10 ± 4% increase in average daily platelet consumption. These measurements could ultimately be used to define a tolerable RPM operating range as well as the effect of the rate of RPM change on platelet activation. Control algorithms might utilize such information to minimize platelet activation and reduce thromboembolic risk.