In Vitro Hemocompatibility Evaluation of Ventricular Assist Devices in Pediatric Flow Conditions: A Benchmark Study

Development of pediatric ventricular assist devices (VADs) has significantly lagged behind that of adult devices. This frustrating reality is reflected by the fact that the Berlin Heart EXCOR VAD is currently the only approved pediatric-specific device in the USA. An alternative option is an off-label use of adult continuous-flow VADs, such as HeartMate II (HMII), which inevitably causes patient-device size mismatch in small children. We sought to conduct in vitro hemocompatibility testing in a pediatric flow condition, with a specific aim to provide benchmark values for future pediatric device development. Given the aforementioned fact that both pulsatile and continuous-flow devices are being used in the pediatric population, we opted to test both types of devices in the present study. The EXCOR and HMII blood pumps were tested using bovine blood under constant hemodynamic conditions (flow rate, Q = 2.5 ± 0.25L/min; differential pressure across the pump, ΔP = 68 ± 5mm Hg). Hemolysis was measured by Harboe assay. There was a steady increase in plasma free hemoglobin during in vitro testing, with a statistically significant difference between 5 and 360 min for both EXCOR (P < 0.0001) and HMII (P < 0.001). However, the degree of an increase in plasma free hemoglobin was more significant with HMII (P < 0.001). Normalized index of hemolysis for EXCOR and HMII were 0.003 ± 0.0026g/100 L and 0.085 ± 0.0119g/100 L, respectively. There was also a steady increase in platelet activation detected by CAPP2A antibody using flow cytometry, with a statistically significant difference between 5 and 360 min for both devices (P < 0.05). The degree of an increase in platelet activation was similar between the two devices (P = 0.218). High molecular weight von Willebrand factor (HMW vWF) multimer degradation measured by immunoblotting was evident for both devices, however, it was more pronounced with the EXCOR. EXCOR blood samples from all three time points (120, 240, and 360 min) were significantly different from the baseline (5 min), whereas only 360 min samples had a significant difference from the baseline with the HMII. In conclusion, we have observed similarities and differences in hemocompatibility profiles between the EXCOR and HMII, both of which are commonly used in the pediatric population. We anticipate the benchmark values in the present study will facilitate future pediatric VAD development.