In vivo evaluation of the miniaturized Gyro centrifugal pump as an implantable ventricular assist device.

A miniaturized Gyro centrifugal pump has been developed to be incorporated into a totally implantable artificial heart. The Gyro PI (permanently implantable) model is a pivot bearing supported centrifugal pump with a priming volume of 20 ml. With the miniaturized actuator, the pump-actuator package has a height of 53 mm, a diameter of 65 mm, and a displacement volume of 145 ml. To evaluate the hemocompatibility and efficiency of the Gyro PI pump system, a plastic prototype (Gyro PI-601) was implanted into a bovine model as a left or right ventricular assist device (LVAD or RVAD), bypassing from the left ventricular apex to the descending aorta or from the right ventricular infundibulum to the main pulmonary artery. The calves were anticoagulated with heparin to maintain activated clotting times from 150 to 200 s. Four calves were supported for 23, 24, and 50 days in the LVAD studies, and 40 days in the RVAD study. The first calf died due to intrathoracic bleeding associated with sepsis. The second calf was euthanized for a low flow rate less than 2 L/min due to an obstructed inflow with growing pannus. The third and fourth calves were euthanized as scheduled. Renal and hepatic functions remained normal, and plasma free hemoglobin values were less than 8 mg/dL throughout the experiments. The fourth case showed flow rates of 4.83 +/- 0.57 L/min, input power of 6.16 +/- 0.49 W, and the inside temperature of the actuator of 43.5 +/- 0.52 degrees C. The pumps implanted in the fourth calf demonstrated no thrombus formation at the autopsy. These in vivo experiments revealed that the Gyro PI pump can provide adequate flow as an easily implantable, efficient, antithrombogenic, and nonhemolytic centrifugal LVAD or RVAD with miniaturized actuators.