Platelet adhesion emulation: A novel method for estimating the device thrombosis potential of a ventricular assist device

Intraventricular flow visualization in different heart failure stages with blood pump support in a mock circulatory loop

The intraventricular blood flow changed by blood pump flow dynamics may correlate with thrombosis and ventricular suction. The flow velocity, distribution of streamlines, vorticity, and standard deviation of velocity inside a left ventricle failing to different extents throughout the cardiac cycle when supported by an axial blood pump were measured by particle image velocimetry (PIV) in this study. The results show slower and static flow velocities existed in the central region of the left ventricle near the mitral valve and aortic valve and that were not sensitive to left ventricular (LV) failure degree or LV pressure. Strong vorticity located near the inner LV wall around the LV apex and the blood pump inlet was not sensitive to LV failure degree or LV pressure. Higher standard deviation of the blood velocity at the blood pump inlet decreased with increasing LV failure degree, whereas the standard deviation of the velocity near the atrium increased with increasing intraventricular pressure. The experimental results demonstrated that the risk of thrombosis inside the failing left ventricle is not related to heart failure degree. The "washout" performance of the strong vorticity near the inner LV wall could reduce the thrombotic potential inside the left ventricle and was not related to heart failure degree. The vorticity near the aortic valve was sensitive to LV failure degree but not to LV pressure. We concluded that the risk of blood damage caused by adverse flow inside the left ventricle decreased with increasing LV pressure.

A two-phase flow approach for modeling blood stasis and estimating the thrombosis potential of a ventricular assist device

Thrombosis and its related events have become a major concern during the development and optimization of ventricular assist devices (VADs, also called blood pumps), and limit their clinical use and economic benefits. Attempts have been made to model the thrombosis formation, considering hemodynamic and biochemical processes. However, the complexities and computational expenses are prohibitive. Blood stasis is one of the key factors which may lead to the formation of thrombosis and excessive thromboembolic risks for patients. This study proposed a novel approach for modeling blood stasis, based on a two-phase flow principle. The locations of blood residual can be tracked over time, so that regions of blood stasis can be identified. The blood stasis in an axial blood pump is simulated under various working conditions, the results agree well with the experimental results. In contrast, conventional hemodynamic metrics such as velocity, time-averaged wall shear stress (TAWSS), and relative residence time (RRT), were contradictory in judging risk of blood stasis and thrombosis, and inconsistent with experimental results. We also found that the pump operating at the designed rotational speed is less prone to blood stasis. The model provides an efficient and fast alternative for evaluating blood stasis and thrombosis potential in blood pumps, and will be a valuable addition to the tools to support the design and improvement of VADs.

A 3-dimensional-printed left ventricle model incorporated into a mock circulatory loop to investigate hemodynamics inside a severely failing ventricle supported by a blood pump

Intraventricular blood stasis is a design consideration for continuous flow blood pumps and might contribute to adverse events such as thrombosis and ventricular suction. However, the blood flow inside left ventricles (LVs) supported by blood pumps is still unclear. In vitro experiments were conducted to imitate how the hydraulic performance of an axial blood pump affects the intraventricular blood flow of a severe heart failure patient, such as velocity distribution, vorticity, and standard deviation of velocity. In this study, a silicone model of the LV was constructed from the computed tomography data of one patient with heart failure and was 3D printed. Then, intraventricular flow was visualized by particle image velocimetry equipment within a mock circulation loop. The results showed that the axial blood pump suctions most of the blood in a severely failing LV, there was an altered flow status within the LV, and blood stasis appeared in the central region of the LV. Some blood may be suctioned from the aortic valve to the blood pump because the patient's native heart was severely failing. Blood stasis at the LV center may cause thrombosis in the LV. The vortex flow near the inner wall of the LV can thoroughly wash the left ventricular cavity.