VAD-CIRCULATION INTERACTION – THE VAD'S PERSPECTIVE

In case of chronic mechanical circulatory support, it is highly desirable to fully understand the interaction between the beating left ventricle and the VAD in order to potentially reduce adverse events. Thus, we took the VAD's perspective and investigated the flow inside a VAD in an advanced development status during the time course of a heartbeat. The study is conducted with computational fluid dynamics (CFD) applying realistic pressure boundary conditions for left ventricular and arterial pressure and the results are compared to results produced with an established, active mock circulation loop. Due to the high resolution in time and space and the use of sliding mesh interfaces, local flow phenomena during different phases of systole and diastole are unmasked. The effects of inertia in the pump and cannulae become evident, which are not modeled in more traditional VAD flow simulations with steady-state boundary conditions. The results show that hysteresis effects due to inertia are quantitatively of high importance. The hysteresis curves of the VAD operational point obtained experimentally and numerically correlate well. Moreover, the results show that a VAD design for a highly pulsed flow can lead to a situation, where almost no remaining stagnation zones, as quantified with a numerical stagnation index, exist during a heartbeat. Despite increased computational costs, highly resolved CFD simulations in time and space with realistic time-varying boundary conditions are a powerful tool to increase understanding of the interaction of the mechanically supported circulation and the device itself. This enabled a verification of a VAD design with low to almost non-existing flow stagnation at constant rotational speed. This finding correlates well with the fact that the VAD does not require any anticoagulation in chronic animal trial testing lasting weeks to months.