Thromboembolism and bleeding remain significant complications of ventricular assist device (VAD) support. Increasing the amount of biocompatibility data collected during preclinical studies can provide additional criteria to evaluate device refinements, while design changes may be implemented before entering clinical use. Twenty bovines were implanted with the EVAHEART centrifugal VAD for durations from 30 to 196 days. Titanium alloy pumps were coated with either diamond-like carbon or 2-methoxyethyloylphosphoryl choline (MPC). Activated platelets and platelet microaggregates were quantified by flow cytometry, including two new assays to quantify bovine platelets expressing CD62P and CD63. Temporally, all assays were low preoperatively, then significantly increased following VAD implantation, before declining to a lower, but still elevated level over 2-3 weeks. MPC-coated VADs produced significantly fewer activated platelets after implant trauma effects diminished. Three animals receiving no postoperative anticoagulation had similar amounts of circulating activated platelets and platelet microaggregates as animals receiving warfarin anticoagulation. Two new methods to quantify bovine activated platelets using antibodies to CD62P and CD63 were characterized and applied. These measures, along with previously described assays, were able to differentiate between two biocompatible coatings and assess effects of anticoagulation regimen in VAD preclinical testing.
The aim of this study was the evaluation of the thrombogenicity and the biocompatibility of the SunMedical EVAHEART left ventricular assist system (LVAS) coated with 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer compared to a diamond-like carbon (DLC) coating. Four calves were implanted with the MPC polymer-coated LVAS. Eight calves were implanted with DLC coated LVAS. The thrombogenicity and biocompatibility of the pumps were evaluated. At explant, 60.0 +/- 37.2% (5-85%) of the pump surface area was still coated with MPC polymer after the duration of 45.0 +/- 32.0 days. In 1 out of 4 MPC and 2 out of 8 DLC coated pumps, there was a very small amount of thrombus around the seal ring; otherwise the blood contacting surfaces were free of thrombus. Major organs were normal except for a few lesions in kidneys from both groups. The MPC polymer coated EVAHEART LVAS seems to have low thrombogenicity and high biocompatibility similar to the DLC coated system. The current study demonstrated that the MPC polymer coating shows great promise for being used as an antithrombogenic substrate for the LVAS due to its ease of application, significant cost benefit, and reduction in anticoagulation therapy in acute postoperative period.
Many types of rotary blood pumps and pump control methods have recently been developed with the goal of clinical use. From experiments, we know that pump flow spontaneously increases during exercise without changing pump control parameters. The purpose of this study was to determine the hemodynamics associated with the long-term observation of calves implanted with centrifugal blood pumps (EVAHEART, Sun Medical Technology Research Corporation, Nagano, Japan). Two healthy female Jersey calves were implanted with devices in the left thoracic cavity. A total of 22 treadmill exercise tests were performed after the 50th postoperative day. During exercise, the following parameters were compared with conditions at rest: heart rate, blood pressure, central venous oxygen saturation (SvO2), pump speed, and pump flow. The pump flow in a cardiac cycle was analyzed by separating the systole and diastole. Compared to the base data, statistically significant differences were found in the following interrelated parameters: the heart rate (66.8 +/- 5.2 vs. 106 +/- 9.7 bpm), mean pump flow (4.8 +/- 0.2 vs. 7.0 +/- 0.3 L/min), and volume of pump flow in diastole (26.0 +/- 1.8 vs. 13.5 +/- 2.5 ml). During exercise, the volume of pump flow in systole was 3 times larger than that measured in diastole. Blood pressure, SvO2, and pump speed did not change significantly from rest to exercise. These results suggested that the mean pump flow depends on the systolic pump flow. Therefore, the increase in the mean pump flow during exercise under constant pump speed was caused by an increase in the heart rate.
A long-term, compact left ventricular assist device (LVAD), the HeartMate III, has been designed and fabricated, featuring a centrifugal pump with a magnetically levitated rotor. The pump has been optimized by in vitro testing to achieve a design point of 7 L/min against 135 mm Hg at high hydrodynamic efficiency (30%) and to be capable of up to 10 L/min under such a load. Furthermore, the pump has demonstrated no mechanical failures, low hemolysis (4-10 mg/dl plasma free Hb), and low thrombogenicity during six (40, 27, 59, 42, 27, and 49-day) in vivo bovine studies.
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