Insights Into the Low Rate of In-Pump Thrombosis With the HeartMate 3: Does the Artificial Pulse Improve Washout?

Abstract

While earlier studies reported no relevant effect of the HeartMate 3 (HM3) artificial pulse (AP) on bulk pump washout, its effect on regions with prolonged residence times remains unexplored. Using numerical simulations, we compared pump washout in the HM3 with and without AP with a focus on the clearance of the last 5% of the pump volume. Results were examined in terms of flush-volume (Vf, number of times the pump was flushed with new blood) to probe the effect of the AP independent of changing flow rate. Irrespective of the flow condition, the HM3 washout scaled linearly with flush volume up to 70% washout and slowed down for the last 30%. Flush volumes needed to washout 95% of the pump were comparable with and without the AP (1.3–1.4 Vf), while 99% washout required 2.1–2.2 Vf with the AP vs. 2.5 Vf without the AP. The AP enhanced washout of the bend relief and near-wall regions. It also transiently shifted or eliminated stagnation regions and led to rapid wall shear stress fluctuations below the rotor and in the secondary flow path. Our results suggest potential benefits of the AP for clearance of fluid regions that might elicit in-pump thrombosis and provide possible mechanistic rationale behind clinical data showing very low rate of in-pump thrombosis with the HM3. Further optimization of the AP sequence is warranted to balance washout efficacy while limiting blood damage.

Fluid–structure interaction modelling of a positive-displacement Total Artificial Heart

“…Washout was simulated using an Eulerian scalar transport model, similar to other approaches to simulating washout in VADs 49 , 50 and TAHs 38 . Other approaches have used a volume of fluid method to treat the old and new blood phases separately 34 , 37 .…”

“…A higher level of washout rate is desirable, as it directly translates to a reduction in blood stagnation time, reducing the possibility of thrombus formation. Washout is a non-linear process however 49 , 50 , comprised of an initial linear increase at low values of washout and a non-linear increase in washout at higher values, where the rate of washout decreases. The washout rate calculated in this study would assume a linear relationship between washout and time, and may describe why the washout rate tapered off in Fig.…”

Preclinical evaluation of the fluid dynamics and hemocompatibility of the Corheart 6 left ventricular assist device

“…The Corheart has a good washout performance, which reduces the exposure time of blood to non‐physiological shear stress and artificial biomaterial surface. Due to narrow clearance and a complex flow field resulting from the competing effect of centrifugal forces and pressure gradients, 17 clearance gaps are closely linked to blood damage and poor washout in blood pumps 24 . To assist old blood removal, the Corheart's secondary pathways are short with a ‘straight line’ shape and small pump size.…”

Microembolic signal monitoring in patients with HeartMate 3 and HeartWare left ventricular assist devices: Association with antithrombotic treatment and cerebrovascular events

“…The artificial pulse of HM 3 could lead to increased turbulence in the system, which could increase prothrombotic shear stress and platelet activation. During the artificial pulse, the sharp and sudden change in velocity leads to a longer exposure time of supraphysiological stresses on the corpuscular components of the blood which could contribute to platelet activation and prothrombotic conditions 41–43 …”

“…During the artificial pulse, the sharp and sudden change in velocity leads to a longer exposure time of supraphysiological stresses on the corpuscular components of the blood which could contribute to platelet activation and prothrombotic conditions. [41][42][43] Georgiadis et al performed one of the few studies with TCD monitoring in 100 healthy controls without a history of cardiovascular disease and detected MES in 5%. 44 In our study MES could be detected in less than 10% of the controls.…”