Physiologic and hematologic concerns of rotary blood pumps: what needs to be improved?

A Multi-Domain Simulation Study of a Pulsatile-Flow Pump Device for Heart Failure With Preserved Ejection Fraction

Mechanical circulatory support (MCS) devices are currently under development to improve the physiology and hemodynamics of patients with heart failure with preserved ejection fraction (HFpEF). Most of these devices, however, are designed to provide continuous-flow support. While it has been shown that pulsatile support may overcome some of the complications hindering the clinical translation of these devices for other heart failure phenotypes, the effects that it may have on the HFpEF physiology are still unknown. Here, we present a multi-domain simulation study of a pulsatile pump device with left atrial cannulation for HFpEF that aims to alleviate left atrial pressure, commonly elevated in HFpEF. We leverage lumped-parameter modeling to optimize the design of the pulsatile pump, computational fluid dynamic simulations to characterize hydraulic and hemolytic performance, and finite element modeling on the Living Heart Model to evaluate effects on arterial, left atrial, and left ventricular hemodynamics and biomechanics. The findings reported in this study suggest that pulsatile-flow support can successfully reduce pressures and associated wall stresses in the left heart, while yielding more physiologic arterial hemodynamics compared to continuous-flow support. This work therefore supports further development and evaluation of pulsatile support MCS devices for HFpEF.

The Influence of Rotary Blood Pump Speed Modulation on the Risk of Intraventricular Thrombosis

Rotary left ventricular assist devices (LVADs) are commonly operated at a constant speed, attenuating blood flow pulsatility. Speed modulation of rotary LVADs has been demonstrated to improve vascular pulsatility and pump washout. The effect of LVAD speed modulation on intraventricular flow dynamics is not well understood, which may have an influence on thromboembolic events. This study aimed to numerically evaluate intraventricular flow characteristics with a speed modulated LVAD. A severely dilated anatomical left ventricle was supported by a HeartWare HVAD in a three-dimensional multiscale computational fluid dynamics model. Three LVAD operating scenarios were evaluated: constant speed and sinusoidal co- and counter-pulsation. In all operating scenarios, the mean pump speed was set to restore the cardiac output to 5.0 L/min. Co- and counter-pulsation was speed modulated with an amplitude of 750 rpm. The risk of thrombosis was evaluated based on blood residence time, ventricular washout, kinetic energy densities, and a pulsatility index map. Blood residence time for co-pulsation was on average 1.8 and 3.7% lower than constant speed and counter-pulsation mode, respectively. After introducing fresh blood to displace preexisting blood for 10 cardiac cycles, co-pulsation had 1.5% less old blood in comparison to counter-pulsation. Apical energy densities were 84 and 27% higher for co-pulsation in comparison to counter-pulsation and constant speed mode, respectively. Co-pulsation had an increased pulsatility index around the left ventricular outflow tract and mid-ventricle. Improved flow dynamics with co-pulsation was caused by increased E-wave velocities which minimized blood stasis. In the studied scenario and from the perspective of intraventricular flow dynamics, co-pulsation of rotary LVADs could minimize the risk of intraventricular thrombosis.

Mathematical Modeling of Rotary Blood Pumps in a Pulsatile In Vitro Flow Environment

Nowadays, sacrificing animals to develop medical devices and receive regulatory approval has become more common, which increases ethical concerns. Although in vivo tests are necessary for development and evaluation of new devices, nonetheless, with appropriate in vitro setups and mathematical models, a part of the validation process can be performed using these models to reduce the number of sacrificed animals. The main aim of this study is to present a mathematical model simulating the hydrodynamic function of a rotary blood pump (RBP) in a pulsatile in vitro flow environment. This model relates the pressure head of the RBP to the flow rate, rotational speed, and time derivatives of flow rate and rotational speed. To identify the model parameters, an in vitro setup was constructed consisting of a piston pump, a compliance chamber, a throttle, a buffer reservoir, and the CentriMag RBP. A 40% glycerin-water mixture as a blood analog fluid and deionized water were used in the hydraulic circuit to investigate the effect of viscosity and density of the working fluid on the model parameters. First, model variables were physically measured and digitally acquired. Second, an identification algorithm based on regression analysis was used to derive the model parameters. Third, the completed model was validated with a totally different set of in vitro data. The model is usable for both mathematical simulations of the interaction between the pump and heart and indirect pressure measurement in a clinical context.

Shear-mediated platelet activation in the free flow: Perspectives on the emerging spectrum of cell mechanobiological mechanisms mediating cardiovascular implant thrombosis

Shear-mediated platelet activation (SMPA) is central in thrombosis of implantable cardiovascular therapeutic devices. Despite the morbidity and mortality associated with thrombosis of these devices, our understanding of mechanisms operative in SMPA, particularly in free flowing blood, remains limited. Herein we present and discuss a range of emerging mechanisms for consideration for "free flow" activation under supraphysiologic shear. Further definition and manipulation of these mechanisms will afford opportunities for novel pharmacologic and mechanical strategies to limit SMPA and enhance overall implant device safety.

Pumping Rate Study of a Left Ventricular Assist Device in a Mock Circulatory System

The aim of this work was to investigate the hemodynamic influence of the change of pump rate on the cardiovascular system with consideration of heart rate and the resonant characteristics of the arterial system when a reliable synchronous triggering source is unavailable. Hemodynamic waveforms are recorded at baseline conditions and with the pump rate of left ventricular assist device (LVAD) at 55, 60, 66, and 70 beats per minute for four test conditions in a mock circulatory system. The total input work (TIW) and energy equivalent pressure (EEP) are calculated as metrics for evaluating the hemodynamic performance within different test conditions. Experimental results show that TIW and EEP achieve their maximum values, where the pump rate is equal to the heart rate. In addition, it demonstrates that TIW and EEP are significantly affected by changing pump rate of LVAD, especially when the pump rate is closing to the natural frequency of the arterial system. When a reliable synchronous triggering source is not available for LVAD, it is suggested that selecting a pump rate equal to the resonant frequency of the arterial system could achieve better supporting effects.

Durable Mechanical Circulatory Support versus Organ Transplantation: Past, Present, and Future

For more than 30 years, heart transplantation has been a successful therapy for patients with terminal heart failure. Mechanical circulatory support (MCS) was developed as a therapy for end-stage heart failure at a time when cardiac transplantation was not yet a useful treatment modality. With the more successful outcomes of cardiac transplantation in the 1980s, MCS was applied as a bridge to transplantation. Because of donor scarcity and limited long-term survival, heart transplantation has had a trivial impact on the epidemiology of heart failure. Surgical implementation of MCS, both for short- and long-term treatment, affords physicians an opportunity for dramatic expansion of a meaningful therapy for these otherwise mortally ill patients. This review explores the evolution of mechanical circulatory support and its potential for providing long-term therapy, which may address the limitations of cardiac transplantation.

Left ventricular assist devices: a kidney's perspective

The left ventricular assist device (LVAD) has become an established treatment option for patients with refractory heart failure. Many of these patients experience chronic kidney disease (CKD) due to chronic cardiorenal syndrome type II, which is often alleviated quickly following LVAD implantation. Nevertheless, reversibility of CKD remains difficult to predict. Interestingly, initial recovery of GFR appears to be transient, being followed by gradual but significant late decline. Nevertheless, GFR often remains elevated compared to preimplant status. Larger GFR increases are followed by a proportionally larger late decline. Several explanations for this gradual decline in renal function after LVAD therapy have been proposed, yet a definitive answer remains elusive. Mortality predictors of LVAD implantation are the occurrence of either postimplantation acute kidney injury (AKI) or preimplant CKD. However, patient outcomes continue to improve as LVAD therapy becomes more widespread, and adverse events including AKI appear to decline. In light of a growing destination therapy population, it is important to understand the cumulative effects of long-term LVAD support on kidney function. Additional research and passage of time are required to further unravel the intricate relationships between the LVAD and the kidney.