In Vitro Hemocompatibility Evaluation of Modified Rotary Left to Right Ventricular Assist Devices in Pulmonary Flow Conditions

Acquired platelet defects are responsible for nonsurgical bleeding in left ventricular assist device recipients

BACKGROUND

Left ventricular assist devices (LVADs) have been used as a standard treatment option for patients with advanced heart failure. However, these devices are prone to adverse events. Nonsurgical bleeding (NSB) is the most common complication in patients with continuous flow (CF) LVADs. The development of acquired von Willebrand syndrome (AVWS) in CF-LVAD recipients is thought to be a key factor. However, AVWS is seen across a majority of LVAD patients, not just those with NSB. The purpose of this study was to examine the link between acquired platelet defects and NSB in CF-LVAD patients.

METHODS

Blood samples were collected from 62 CF-LVAD patients at pre- and 4 post-implantation timepoints. Reduced adhesion receptor expression (GPIbα and GPVI) and activation of platelets (GPIIb/IIIa activation) were used as markers for acquired platelet defects.

RESULTS

Twenty-three patients experienced at least one NSB episode. Significantly higher levels of platelet activation and receptor reduction were seen in the postimplantation blood samples from bleeders compared with non-bleeders. All patients experienced the loss of high molecular weight monomers (HMWM) of von Willebrand Factor (vWF), but no difference was seen between the two groups. Multivariable logistic regression showed that biomarkers for reduced platelet receptor expression (GPIbα and GPVI) and activation (GPIIb/IIIa) have more predictive power for NSB, with the area under curve (AUC) values of 0.72, 0.68, and 0.62, respectively, than the loss of HMWM of vWF (AUC: 0.57).

CONCLUSION

The data from this study indicated that the severity of acquired platelet defects has a direct link to NSB in CF-LVAD recipients.

Hemolysis Testing In Vitro: A Review of Challenges and Potential Improvements

Many medical devices such as cardiopulmonary bypass systems, mechanical heart valves, or ventricular assist devices are intended to come into contact with blood flow during use. In vitro hemolysis testing can provide valuable information about the hemocompatibility of prototypes and thus help reduce the number of animal experiments required. Such tests play an important role as research and development tools for objective comparisons of prototypes and devices as well as for the extrapolation of their results to clinical outcomes. Therefore, it is important to explore and provide new ways to improve current practices. In this article, the main challenges of hemolysis testing are described, namely the difficult blood sourcing, the high experimental workload, and the low reproducibility of test results. Several approaches to address the challenges identified are proposed and the respective literature is reviewed. These include the replacement of blood as the "shear-sensitive fluid" by alternative test fluids, the replacement of sparse, manual sampling and blood damage assessment by a continuous and automated monitoring, as well as an analysis of categories and causes of variability in hemolysis test results that may serve as a structural template for future studies.

The porcine abattoir blood model-Evaluation of platelet function for in-vitro hemocompatibility investigations

BACKGROUND

The major obstacle of blood-contacting medical devices is insufficient hemocompatibility, particularly thrombogenicity and platelet activation. Pre-clinical in-vitro testing allows for the evaluation of adverse thrombogenicity-related events, but is limited, among others, by the availability and quantity of human blood donations. The use of animal blood is an accepted alternative for several tests; however, animal and particularly abattoir blood might present species-specific differences to human blood as well as elevated blood values, and pre-activated platelets due to stressed animals and non-standardized blood collection.

MATERIAL & METHODS

To this end, we investigated porcine abattoir blood in comparison to human donor blood with the focus on platelet pre-activation and remaining activation potential. By means of light transmission aggregometry, aggregation kinetics of platelet rich plasma after stimulation with three different concentrations of each adenosine diphosphate (ADP) (5 µM, 10 µM, 20 µM) and collagen (2.5 µg/ml, 5 µg/ml, 10 µg/ml) were monitored.

RESULTS

The activation with collagen revealed no significant differences in platelet behavior of the two species. In contrast, stimulation with ADP resulted in a lower maximum aggregation and a high disaggregation for porcine abattoir blood. The latter is a species-specific phenomenon of porcine platelets. Variations within each study cohort were comparable for human and abattoir pig.

CONCLUSION

The similarities in platelet activation following collagen stimulation and the preservation of the porcine-specific reaction to ADP prove a general functionality of the abattoir blood. This finding provides a first step towards the complete validation of the porcine abattoir blood model.

In vitro Hemocompatibility Evaluation of the HeartWare Ventricular Assist Device Under Systemic, Pediatric and Pulmonary Support Conditions

The development of adult use right ventricular assist devices (RVADs) and pediatric left ventricular assist devices (pediatric LVADs) have significantly lagged behind compared to adult use left ventricular assist devices (LVADs). The HeartWare ventricular assist device (HVAD) intended to be used for adult's systemic support, is increasingly used off-label for adult pulmonary and pediatric systemic support. Due to different hemodynamics and physiology, however, the HVAD's hemocompatibility profiles can be drastically different when used in adult pulmonary circulation or in children, compared to its intended usage state, which could have a direct clinical and developmental relevance. Taking these considerations in mind, we sought to conduct in vitro hemocompatibility testing of HVAD in adult systemic, pediatric systemic and adult pulmonary support conditions. Two HVADs coupled to custom-built blood circulation loops were tested for 6 hours using bovine blood at 37°C under adult systemic, pediatric systemic, and adult pulmonary flow conditions (flow rate = 5.0, 2.5, and 4.5 L/min; differential pressure = 100, 69, and 20 mm Hg, respectively). Normalized index of hemolysis for adult systemic, pediatric systemic, and adult pulmonary conditions were 0.0083, 0.0039, and 0.0017 g/100 L, respectively. No significant difference was seen in platelet activation for these given conditions. High molecular weight von Willebrand factor multimer degradation was evident in all conditions (p < 0.05). In conclusion, alterations in the usage mode produce substantial differences in hemocompatibility of the HVAD. These findings would not only have clinical relevance but will also facilitate future adult use RVAD and pediatric LVAD development.

Extracorporeal Membrane Oxygenation-Induced Hemolysis: An In Vitro Study to Appraise Causative Factors

In vitro hemolysis testing is commonly used to determine hemocompatibility of ExtraCorporeal Membrane Oxygenation (ECMO). However, poor reproducibility remains a challenging problem, due to several unidentified influencing factors. The present study investigated potential factors, such as flow rates, the use of anticoagulants, and gender of blood donors, which could play a role in hemolysis. Fresh human whole blood was anticoagulated with either citrate (n = 6) or heparin (n = 12; 6 female and 6 male blood donors). Blood was then circulated for 360 min at 4 L/min or 1.5 L/min. Regardless of flow rate conditions, hemolysis remained unchanged over time in citrated blood, but significantly increased after 240 min circulation in heparinized blood (p ≤ 0.01). The ratio of the normalized index of hemolysis (NIH) of heparinized blood to citrated blood was 11.7-fold higher at 4 L/min and 16.5–fold higher at 1.5 L/min. The difference in hemolysis between 1.5 L/min and 4 L/min concurred with findings of previous literature. In addition, the ratio of NIH of male heparinized blood to female was 1.7-fold higher at 4 L/min and 2.2-fold higher at 1.5 L/min. Our preliminary results suggested that the choice of anticoagulant and blood donor gender could be critical factors in hemolysis studies, and should be taken into account to improve testing reliability during ECMO.