In-Vitro Assessment of the Thrombogenic Potential of Heart Valve Prostheses
Benjamin Grossmann, Torsten Linde, Thomas Schmitz-Rode, Ulrich Steinseifer.
RWTH Aachen University, Aachen, Germany.
OBJECTIVE: The thrombogenic potential of cardiovascular devices is usually assessed in animal studies. However, these studies are elaborate and expensive, and the predictability of the clinical performance is limited. In this study, we introduce a new methodology for an in vitro assessment of the thrombogenic potential of heart valve prostheses.
METHODS: The new methodology consists of the combination of numerical and experimental flow studies as well as in vitro blood testing. The principle is shown in fig. 1.Accordingly, a numerical model of the valve configuration was set up and experimentally validated by digital particle velocimetry (PIV). The model allows for the identification of risk areas for thrombus formation, e.g., stall flow, recirculation, flow separation, shear rates, etc. In parallel, blood tests were performed with porcine blood under physiological conditions in a specifically designed pulse duplicator. Specific protocols were developed for blood treatment and analysis e.g. regarding anticoagulation, platelet activation etc. Early thrombus formation was detected by changes in blood parameters and acoustic signals. The test procedure was validated with in vivo data, i.e., animal studies and published clinical results. Finally, detected thrombus locations were correlated with the risk areas identified by the numerical modelling. A correlation index CI was defined for high (CI=1) to low (CI=0) probability of thrombus formation.
RESULTS: The blood tests showed good agreement with in vivo data. The correlation of numerical studies and thrombus location led to a realistic correlation matrix of flow characteristics and potential for thrombus formation. In example, the highest risk for thrombus formation (CI=0,91) was identified in isolated flow recirculation or separation areas, but it already decreased drastically if the recirculation / separation is immediately followed by an increasing shear rate in flow direction (CI=0,22).
The new approach of combining numerical and experimental flow measurement with blood testing provides a better understanding of the flow induced mechanisms of clot formation in heart valve prostheses, and thus may be a valuable instrument in assessing their thrombogenic potential.
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