Multiscale Analysis of the Interactions Between a Novel Total Artificial Heart and the Native Cardiovascular System

: (Alternative Format Thesis)

Abstract

Cardiovascular diseases, in particular heart failure, represent a significant global health burden which is only expected to worsen in the coming decades. For those suffering from end-stage heart failure, a heart transplant is considered the gold standard treatment. However, the limited availability of suitable donor hearts has led to unnecessary patient deaths whilst they await a transplant. Mechanical circulatory support (MCS) devices, such as ventricular assist devices (VADs) and total artificial hearts (TAHs) offer the possibility of alleviating this shortfall and extending the life of the patient. These devices partially or fully support the pumping capacity of the heart, bridging the gap to when a suitable donor heart is available. The Realheart TAH, developed by Scandinavian Real Heart, is a novel positive-displacement MCS device that aims to overcome issues surrounding the current generation of TAHs.

In silico modelling approaches, such as computational fluid dynamics (CFD), can offer unique insights into device performance and operation that may not be obtainable from conventional experimental approaches. Rotary MCS has been extensively studied using these methods whilst positive-displacement devices are under-researched. This thesis aims to understand the performance of and interaction between the Realheart TAH and the native cardiovascular system through the use of bespoke computational modelling approaches.

Initially, a modelling strategy was developed for the unique fluid-driven motion of the bileaflet flow control valves in the Realheart TAH using a combined fluid-structure interaction (FSI) and CFD approach. This approach allowed the valve motion to adapt to changes in the flow field, enabling the assessment of any operating condition. By combining overset meshing, variable time-stepping, a blend of weak and strong coupling between the structural and fluid flow solvers and lumped parameter downstream boundary condition, the strategy was shown to effectively capture leaflet dynamics in a simplified positive-displacement pump with a physiological pressure response and high-resolution wall shear stress data.

The adaptive valve motion method was integrated into a complete model of the Realheart TAH to assess the performance of the device over a range of operating conditions. The model was validated against in vitro data from a hybrid cardiovascular simulator, showing strong agreement across all operating conditions, demonstrating the robustness and accuracy of the modelling approach. Key parameters such as cardiac output, pulse pressure, ventricular washout and shear stress increased with stroke length and heart rate, whilst unique valve kinematics were observed, including asymmetrical valve leaflet closure and leaflet flutter. The model highlighted low blood stagnation and low shear stress, indicating a reduced risk to clot formation and mechanically induced blood damage.

Methods for the assessment of haemolysis, the rupture of red blood cells and the leakage of haemoglobin, have typically only been investigated using rotary flow blood pumps. Shear-based Eulerian scalar-transport and Lagrangian particle-tracking approaches to modelling haemolysis were investigated and compared for their efficacy and suitability at capturing haemolytic mechanisms in the Realheart TAH. Persistent high shear leakage flow past a closed valve was found to be the primary contributor to haemolysis, driven by pressure gradients across the closed valve. The Eulerian method proved more robust and reliable at capturing this effect, as well as providing improved visualisation.

The haemolytic potential of two generations of the Realheart TAH was then analysed across different cardiac outputs using the Eulerian scalar-transport method and a modified integral method for faster haemolysis assessment. Haemolysis in the two devices was similar, and increased non-linearly with cardiac output for both device designs, correlating with an increase in pressure head. The integral method was also able to match the result generated by the scalar-transport approach, offering an efficient alternative. Both versions of the device produced haemolysis results that were lower than rotary pumps from the literature, indicating improved biocompatibility with the Realheart TAH.

Overall, this thesis demonstrates that in silico modelling is a valuable tool for designing and optimising positive-displacement TAHs. The insights gained from this research highlight the potential for advanced numerical methods to reduce the reliance on costly and time-consuming experimental testing, accelerating the development and regulatory approval of MCS devices.

Date of Award	7 May 2025
Original language	English
Awarding Institution	University of Bath
Supervisor	Katharine Fraser (Supervisor), Andrew Cookson (Supervisor) & Richie Gill (Supervisor)