Numerical Analysis of Blood Damage Potential of the HeartMate II and HeartWare HVAD Rotary Blood Pumps

Abstract

Implantable left ventricular assist devices (LVADs) became the therapy of choice in treating end-stage heart failure. Although survival improved substantially and is similar in currently clinically implanted LVADs HeartMate II (HM II) and HeartWare HVAD, complications related to blood trauma are frequently observed. The aim of this study was to compare these two pumps regarding their potential blood trauma employing computational fluid dynamics. High-resolution structured grids were generated for the pumps. Newtonian flow was calculated, solving Reynolds-averaged Navier-Stokes equations with a sliding mesh approach and a k-ω shear stress transport turbulence model for the operating point of 4.5 L/min and 80 mm Hg. The pumps were compared in terms of volumes subjected to certain viscous shear stress thresholds, below which no trauma was assumed (von Willebrand factor cleavage: 9 Pa, platelet activation: 50 Pa, and hemolysis: 150 Pa), and associated residence times. Additionally, a hemolysis index was calculated based on a Eulerian transport approach. Twenty-two percent of larger volumes above 9 Pa were observed in the HVAD; above 50 Pa and 150 Pa the differences between the two pumps were marginal. Residence times were higher in the HVAD for all thresholds. The hemolysis index was almost equal for the HM II and HVAD. Besides the gap regions in both pumps, the inlet regions of the rotor and diffuser blades have a high hemolysis production in the HM II, whereas in the HVAD, the volute tongue is an additional site for hemolysis production. Thus, in this study, the comparison of the HM II and the HVAD using numerical methods indicated an overall similar tendency to blood trauma in both pumps. However, influences of turbulent shear stresses were not considered and effects of the pivot bearing in the HM II were not taken into account. Further in vitro investigations are required.

Scaling the Low-Shear Pulsatile TORVAD for Pediatric Heart Failure

“…Thamsen et al used computational fluid dynamic simulations to model the flow in the HMII and HVAD pumps to understand the blood damage potential of CF devices (21, 22). They calculated the volume of blood above approximate thresholds for vWF unfolding (9 Pa), platelet activation (50 Pa), and hemolysis (150 Pa) as a way of quantifying the damage potential of a device.…”

Microfludic platforms for the evaluation of anti-platelet agent efficacy under hyper-shear conditions associated with ventricular assist devices

“…Interestingly, limited insight exists as to their efficacy in inhibiting mechanical agonists such as physical stimuli (i.e., shear stress), which are dominant drivers of thrombosis in VADs. Indeed, VADs are characterized by narrow geometries, where flowing blood undergoes rapid accelerations and platelets are subjected to non-physiologic, extreme levels of shear stress and fast dynamics, as reported in different numerical studies in which the fluid dynamics in real devices was simulated [9,10]. In particular, in the study by Chiu and co-authors [10], shear stress patterns along platelet trajectories in two commercial axial VADs were analyzed under normal operating conditions, corresponding to a cardiac output of 4 L/min: such patterns of shear stress are characterized by peaks of shear magnitude in the range 100–300 Pa, significantly higher than physiological values (1 – 5 Pa).…”

Modelagem matemática da fluidodinâmica não-newtoniana e bifásica simplificada da hemólise induzida mecanicamente em sistemas de bombeamento centrífugo de sangue

“…Esses modelos têm sido amplamente utilizados, principalmente a equação (1.2), nas simulações computacionais, embora sejam bastante observados resultados superestimados em, no mínimo, uma ordem de grandeza (De Wachter e Verdonck, (Arora et al, 2004), , (Behbahani et al, 2009), (Yu et al, 2017). Apesar disto, o seu uso ainda tem sido considerado pelos engenheiros para tarefas de comparação e otimização de projetos (Thamsen et al, 2015).…”

“…Por exemplo, em um trabalho mais recente (Thamsen et al, 2015), a equação (1.2) foi diferenciada em relação ao tempo resultando em uma equação para a taxa de produção de hemólise na seguinte forma:…”

“…Foi então aplicado em simulações numérico-computacionais e gerou resultados qualitativamente corretos, que mostram ocorrência acentuada de hemólise nas regiões com gradiente elevado de velocidades. Uma avaliação quantitativa mais rigorosa está no aguardo de resultados de experimentos in vitro (Thamsen et al, 2015), (Schüle et al, 2016).…”