Development of the Baylor Gyro permanently implantable centrifugal blood pump as a biventricular assist device

The Baylor Gyro permanently implantable centrifugal blood pump (Gyro PI pum p) has been under development since 1995 at Baylor College of Medicine. Exc ellent results were achieved as a left ventricular assist device (LVAD) wit h survival up to 284 days. Based on these results, we are now focusing on t he development of a biventricular assist device (BVAD) system, which requir es 2 pumps to be implanted simultaneously in the preperitoneal space. Our h ypothesis was that the Gyro PI pump would be an appropriate device for an i mplantable BVAD system. The Gyro PI 700 pump is fabricated from titanium al loy and has a 25 ml priming volume, pump weight of 204 g, height of 45 mm, and pump diameter of 65 mm. This pump can provide 5 L/min against 100 mm Hg at 2,000 rpm. In this study, 6 half-Dexter healthy calves have been used a s the experimental model. The right pump was applied between the infundibul ar of the right ventricle and the main pulmonary artery. The left pump was applied between the apex of the left ventricle and the thoracic descending aorta. As for anticoagulation, heparin was administered at the first postop erative week and then converted to warfarin sodium from the second week aft er surgery. Both pump flow rates were controlled maintaining a pulmonary ar terial flow of less than 160 ml/kg/min for the sake of avoidance of pulmona ry congestion. Blood sampling was done to assess visceral organ function, a nd the data regarding pump performance were collected. After encountering t he endpoint, which the study could not keep for any reasons, necropsy and h istopathological examinations were performed. The first 2 cases were termin ated within 1 week. Deterioration of the pump flow due to suction phenomeno n was recognized in both cases. To avoid the suction phenomenon, a flexible conduit attached on the inlet conduit was designed and implanted. After us ing the flexible inflow conduit, the required power and the rotational spee d were reduced. Furthermore, the suction phenomenon was not observed except for 1 case. There was no deterioration regarding visceral organ function, and pulmonary function was maintained within normal range except for 1 case . Even though the experimental animal survived up to 45 days with the flexi ble inflow conduit, an increase in power consumption due to thrombus format ion behind the impeller became a problem. Lower rotational speed, which was probably produced by the effectiveness of the flexible inflow conduit, was speculated to be one of the reasons. And the minimum range of rotational s peed was 1,950 rpm in these 6 BVAD cases and the previous 3 cases of LVAD. In conclusion, 6 cases of BVAD implantation were performed as in vivo anima l studies and were observed up to 45 days. The flexible inflow conduit was applied in 4 of 6 cases, and it was effective in avoiding a suction phenome non. The proper rotational speed of the Gyro PI 700 pump was detected from the viewpoint of antithrombogenicity, which is more than 1,950 rpm.