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.

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Ovines are a common animal model for preclinical evaluation of cardiovascular devices including heart valves, endovascular grafts, and ventricular assist devices. Biocompatibility is essential to the success of these devices; however, tools to assess biocompatibility in ovines are limited. To address this need, antibodies that bind to activated human and bovine platelets and annexin V protein were evaluated for potential cross-reactivity to activated ovine platelets. These candidate markers were incubated with stimulated and quiescent ovine whole blood, and binding to platelets was quantified by flow cytometry. Several antihuman CD62P antibodies including one polyclonal antibody, three monoclonal antibodies, and annexin V selectively bound to activated ovine platelets. An assay to quantify platelet microaggregates was also developed. The availability of assays to quantify ovine platelet activation can increase the quality of biocompatibility data obtainable during preclinical development of artificial organs in the ovine model, potentially aiding in the evaluation of design refinements to enhance device biocompatibility. KeywordsBiocompatibility; Flow cytometry; Ovine platelets; Cardiovascular devices; Platelet activation Ovines are a common animal model for preclinical testing of blood-contacting cardiovascular devices including mechanical heart valves, endovascular grafts, and ventricular assist devices (VADs) (1-4). A critical aspect in the design of these devices is the evaluation of their blood biocompatibility. Yet, the biocompatibility data that can be obtained in ovine studies is limited due to a paucity of available assays for evaluating circulating blood elements during the implant period. In particular, there has only been one report on the use of flow cytometry to evaluate ovine platelet activation in platelet-rich plasma, and there have been no reports in the literature using such techniques to assess temporal platelet activation in ovines implanted with cardiovascular devices (5).Flow cytometry permits surface expression of platelet activation-dependent epitopes to be quantified, providing insight on circulating platelets not obtainable with platelet aggregometry and plasma assays for β-thromboglobulin and platelet factor 4 (6). Circulating activated platelets have been measured in patients with stents, mechanical heart valves, and VADs as well as in patients suffering from acute myocardial infarction and ischemic stroke [7][8][9][10][11][12][13]. The presence of circulating activated platelets has been suggested as a marker for increased risk of thrombotic complications (10). Previously, we have described several flow cytometric assays to quantify circulating activated bovine platelets and platelet microaggregates (14). These assays have been applied to assess circulating activated platelets in calves implanted with rotary VADs (14,15). The results demonstrate the ongoing presence of circulating activated platelets after the effects of surgery (without extracorporeal circulation) have di...