Vascular pulsatility in patients with a pulsatile- or continuous-flow ventricular assist device

Pulsatile Left Ventricular Assistance in High-Risk Percutaneous Coronary Interventions: Short-Term Outcomes

OBJECTIVES

To document the real-world experience with the use of pneumatic pulsatile mechanical circulatory support (MCS) with the PulseCath iVAC2L during high-risk percutaneous coronary interventions (HR-PCIs). Background: The use of MCS in HR-PCIs may reduce the rate of major adverse cardiovascular events (MACEs) at 90 days. The PulseCath iVAC2L is a short-term pulsatile transaortic left ventricular (LV) assist device that has been in use since 2014. The iVAC2L Registry tracks its safety and efficacy in a variety of hospitals worldwide. Methods: The iVAC2L Registry is a multicenter, observational registry that aggregates clinical data from patients treated with the iVAC2L worldwide. A total of 293 consecutive cases were retrospectively collected and analyzed. Estimated rates of in-hospital clinical endpoints were described. All-cause mortality was used as the primary endpoint and other outcomes of interest were used as secondary endpoints. The rates obtained were reported and contextualized. Results: The in-hospital rate of all-cause mortality was 1.0%, MACE was 3.1%. Severe hypotension occurred in 8.9% of patients. Major bleeding and major vascular complications occurred in 1.0% and 2.1%, respectively. Acute myocardial infarction occurred in 0.7% of patients. Cerebrovascular events occurred in 1.4% of patients. Cardiac arrest occurred in 1.7% of patients. A statistically significant improvement in blood pressure was observed with iVAC2L activation. Conclusions: The results of the present study suggest that the iVAC2L is capable of improving hemodynamics with a low rate of adverse events. However, confirmatory studies are needed to validate these findings.

Computational investigation of outflow graft variation impact on hemocompatibility profile in LVADs

BACKGROUND

Hemocompatibility-related adverse events (HRAE) occur commonly in patients with left ventricular assist devices (LVADs) and add to morbidity and mortality. It is unclear whether the outflow graft orientation can impact flow conditions leading to HRAE. This study presents a simulation-based approach using exact patient anatomy from medical images to investigate the influence of outflow cannula orientation in modulating flow conditions leading to HRAEs.

METHODS

A 3D model of a proximal aorta and outflow graft was reconstructed from a computed tomography (CT) scan of an LVAD patient and virtually modified to model multiple cannula orientations (n = 10) by varying polar (cranio-caudal) (n = 5) and off-set (anterior-posterior) (n = 2) angles. Time-dependent computational flow simulations were then performed for each anatomical orientation. Qualitative and quantitative hemodynamics metrics of thrombogenicity including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), endothelial cell platelet activation potential (ECAP), particle residence time (PRT), and platelet activation potential (PLAP) were analyzed.

RESULTS

Within the simulations performed, endothelial cell activation potential (ECAP) and particle residence time (PRT) were found to be lowest with a polar angle of 85°, regardless of offset angle. However, polar angles that produced parameters at levels least associated with thrombosis varied when the offset angle was changed from 0° to 12°. For offset angles of 0° and 12° respectively, flow shear was lowest at 65° and 75°, time averaged wall shear stress (TAWSS) was highest at 85° and 35°, and platelet activation potential (PLAP) was lowest at 65° and 45°.

CONCLUSION

This study suggests that computational fluid dynamic modeling based on patient-specific anatomy can be a powerful analytical tool when identifying optimal positioning of an LVAD. Contrary to previous work, our findings suggest that there may be an "ideal" outflow cannula for each individual patient based on a CFD-based hemocompatibility profile.

Preservation of pulsatility with universal ventricular assist device: In vitro assessment for biventricular support

BACKGROUND

The objective of this study was to assess the pulsatility preservation capability of the universal ventricular assist device (UVAD) when used as a biventricular assist device (BVAD). This evaluation was conducted through an in vitro experiment, utilizing a pulsatile biventricular circulatory mock loop.

METHODS

Two UVAD pumps were tested in a dual setup (BVAD) in the circulatory model with the simulated conditions of left heart failure (HF), right HF, and moderate/severe biventricular HF (BHF). The total flow, aortic pulse pressure, the pulse augmentation factor (PAF), the energy-equivalent pressure (EEP), and the surplus hemodynamic energy (SHE) were observed at various pump speeds to evaluate the pulsatility.

RESULTS

The aortic pulse pressure increased from the baseline (without pump) in all simulated hemodynamic conditions. The PAF ranged from 17%-35% in healthy, left HF, right HF, and mild BHF conditions, with the highest PAF of 90% being observed in the severe BHF condition. The EEP correlated with LVAD flow in all groups (R2  = 0.87-0.97) and increased from the baseline in all cases. The SHE peaked at approximately 5-6 L/min of LVAD support and was likely to decrease at higher LVAD pump flow. The largest decrease in SHE from the baseline, 53%, was observed in the mild BHF conditions with the highest LVAD and RVAD support.

CONCLUSIONS

The UVAD successfully demonstrated the ability to preserve pulsatility in vitro, and to optimize the cardiac output, as an isolated circulatory support device option (RVAD or LVAD) and when used for BVAD support.

Benchtop Models of Patient-Specific Intraventricular Flow During Heart Failure and LVAD Support

The characterization of intraventricular flow is critical to evaluate the efficiency of fluid transport and potential thromboembolic risk but challenging to measure directly in advanced heart failure (HF) patients with left ventricular assist device (LVAD) support. The study aims to validate an in-house mock loop (ML) by simulating specific conditions of HF patients with normal and prosthetic mitral valves (MV) and LVAD patients with small and dilated left ventricle volumes, then comparing the flow-related indices result of vortex parameters, residence time (RT), and shear-activation potential (SAP). Patient-specific inputs for the ML studies included heart rate, end-diastolic and end-systolic volumes, ejection fraction, aortic pressure, E/A ratio, and LVAD speed. The ML effectively replicated vortex development and circulation patterns, as well as RT, particularly for HF patient cases. The LVAD velocity fields reflected altered flow paths, in which all or most incoming blood formed a dominant stream directing flow straight from the mitral valve to the apex. RT estimation of patient and ML compared well for all conditions, but SAP was substantially higher in the LVAD cases of the ML. The benchtop system generated comparable and reproducible hemodynamics and fluid dynamics for patient-specific conditions, validating its reliability and clinical relevance. This study demonstrated that ML is a suitable platform to investigate the fluid dynamics of HF and LVAD patients and can be utilized to investigate heart-implant interactions.

Acausal Modelling of Advanced-Stage Heart Failure and the Istanbul Heart Ventricular Assist Device Support with Patient Data

BACKGROUND

In object-oriented or acausal modelling, components of the model can be connected topologically, following the inherent structure of the physical system, and system equations can be formulated automatically. This technique allows individuals without a mathematics background to develop knowledge-based models and facilitates collaboration in multidisciplinary fields like biomedical engineering. This study conducts a preclinical evaluation of a ventricular assist device (VAD) in assisting advanced-stage heart failure patients in an acausal modelling environment.

METHODS

A comprehensive object-oriented model of the cardiovascular system with a VAD is developed in MATLAB/SIMSCAPE, and its hemodynamic behaviour is studied. An analytically derived pump model is calibrated for the experimental prototype of the Istanbul Heart VAD. Hemodynamics are produced under healthy, diseased, and assisted conditions. The study features a comprehensive collection of advanced-stage heart failure patients' data from the literature to identify parameters for disease modelling and to validate the resulting hemodynamics.

RESULTS

Regurgitation, suction, and optimal speeds are identified, and trends in different hemodynamic parameters are observed for the simulated pathophysiological conditions. Using pertinent parameters in disease modelling allows for more accurate results compared to the traditional approach of arbitrary reduction in left ventricular contractility to model dilated cardiomyopathy.

CONCLUSION

The current research provides a comprehensive and validated framework for the preclinical evaluation of cardiac assist devices. Due to its object-oriented nature, the featured model is readily modifiable for other cardiovascular diseases for studying the effect of pump operating conditions on hemodynamics and vice versa in silico and hybrid mock circulatory loops. The work also provides a potential teaching tool for understanding the pathophysiology of heart failure, diagnosis rationale, and degree of assist requirements.

The Impact of Left Ventricular Assist Device Outflow Graft Positioning on Aortic Hemodynamics: Improving Flow Dynamics to Mitigate Aortic Insufficiency

Heart failure is a global health concern with significant implications for healthcare systems. Left ventricular assist devices (LVADs) provide mechanical support for patients with severe heart failure. However, the placement of the LVAD outflow graft within the aorta has substantial implications for hemodynamics and can lead to aortic insufficiency during long-term support. This study employs computational fluid dynamics (CFD) simulations to investigate the impact of different LVAD outflow graft locations on aortic hemodynamics. The introduction of valve morphology within the aorta geometry allows for a more detailed analysis of hemodynamics at the aortic root. The results demonstrate that the formation of vortex rings and subsequent vortices during the high-velocity jet flow from the graft interacted with the aortic wall. Time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) indicate that modification of the outflow graft location changes mechanical states within the aortic wall and aortic valve. Among the studied geometric factors, both the height and inclination angle of the LVAD outflow graft are important in controlling retrograde flow to the aortic root, while the azimuthal angle primarily determines the rotational direction of blood flow in the aortic arch. Thus, precise positioning of the LVAD outflow graft emerges as a critical factor in optimizing patient outcomes by improving the hemodynamic environment.

Pulsatile Pressure Delivery of Continuous-Flow Left Ventricular Assist Devices Is Markedly Reduced Relative to Heart Failure Patients

Although continuous-flow left ventricular assist devices (CF-LVADs) provide an augmentation in systemic perfusion, there is a scarcity of in vivo data regarding systemic pulsatility on support. Patients supported on CF-LVAD therapy (n = 71) who underwent combined left/right catheterization ramp study were included. Aortic pulsatility was defined by the pulsatile power index (PPI), which was also calculated in a cohort of high-output heart failure (HOHF, n = 66) and standard HF cohort (n = 44). PPI was drastically lower in CF-LVAD-supported patients with median PPI of 0.006 (interquartile range [IQR], 0.002-0.012) compared with PPI in the HF population at 0.09 (IQR, 0.06-0.17) or HOHF population at 0.25 (IQR, 0.13-0.37; p < 0.0001 among groups). With speed augmentation during ramp, PPI values fell quickly in patients with higher PPI at baseline. PPI correlated poorly with left ventricular ejection fraction (LVEF) in all groups. In CF-LVAD patients, there was a stronger correlation with LV dP/dt (r = 0.41; p = 0.001) than LVEF (r = 0.21; p = 0.08; pint < 0.001). CF-LVAD support is associated with a dramatic reduction in arterial pulsatility as measured by PPI relative to HOHF and HF cohorts and decreases with speed. Further work is needed to determine the applicability to the next generation of device therapy.

Venting during venoarterial extracorporeal membrane oxygenation

Cardiogenic shock and cardiac arrest contribute pre-dominantly to mortality in acute cardiovascular care. Here, veno-arterial extracorporeal membrane oxygenation (VA-ECMO) has emerged as an established therapeutic option for patients suffering from these life-threatening entities. VA-ECMO provides temporary circulatory support until causative treatments are effective and enables recovery or serves as a bridging strategy to surgical ventricular assist devices, heart transplantation or decision-making. However, in-hospital mortality rate in this treatment population is still around 60%. In the recently published ARREST trial, VA-ECMO treatment lowered mortality rate in patients with ongoing cardiac arrest due to therapy refractory ventricular fibrillation compared to standard advanced cardiac life support in selected patients. Whether VA-ECMO can reduce mortality compared to standard of care in cardiogenic shock has to be evaluated in the ongoing prospective randomized studies EURO-SHOCK (NCT03813134) and ECLS-SHOCK (NCT03637205). As an innate drawback of VA-ECMO treatment, the retrograde aortic flow could lead to an elevation of left ventricular (LV) afterload, increase in LV filling pressure, mitral regurgitation, and elevated left atrial pressure. This may compromise myocardial function and recovery, pulmonary hemodynamics—possibly with concomitant pulmonary congestion and even lung failure—and contribute to poor outcomes in a relevant proportion of treated patients. To overcome these detrimental effects, a multitude of venting strategies are currently engaged for both preventive and emergent unloading. This review aims to provide a comprehensive and structured synopsis of existing venting modalities and their specific hemodynamic characteristics. We discuss in detail the available data on outcome categories and complication rates related to the respective venting option.

Graphical abstract

The hemodynamics and blood trauma in axial blood pump under different operating model

Speed modulation of blood pump has been proved to help restore vascular pulsatility and implemented clinically during treatment for cardiac failure. However, its effect on blood trauma has not been studied thoroughly. In this paper, we study the flow field of an axial pump FW-X under the modes of co-pulse, counter pulse and constant speed to evaluate the blood trauma. Based on the coupling model of cardiovascular system and axial blood pump, aortic pressure and the pump flow were obtained and applied as the boundary conditions at the pump outlet and inlet. The level of shear stress and hemolysis index were derived from computational fluid dynamics (CFD) simulation. Results showed the constant speed mode had the lowest shear stress level and hemolytic index at the expense of diminished pulsatility. Compared with the constant speed mode, the hemolysis index of co-pulse and counter pulse mode was higher, but it was helpful to restore vascular pulsatility. This method can be easily incorporated in the in vitro testing phase to analyze and decrease a pump's trauma before animal experimentation, thereby reducing the cost of blood pump development.

Physiology of Continuous-Flow Left Ventricular Assist Device Therapy

The expanding use of continuous-flow left ventricular assist devices (CF-LVADs) for end-stage heart failure warrants familiarity with the physiologic interaction of the device with the native circulation. Contemporary devices utilize predominantly centrifugal flow and, to a lesser extent, axial flow rotors that vary with respect to their intrinsic flow characteristics. Flow can be manipulated with adjustments to preload and afterload as in the native heart, and ascertainment of the predicted effects is provided by differential pressure-flow (H-Q) curves or loops. Valvular heart disease, especially aortic regurgitation, may significantly affect adequacy of mechanical support. In contrast, atrioventricular and ventriculoventricular timing is of less certain significance. Although beneficial effects of device therapy are typically seen due to enhanced distal perfusion, unloading of the left ventricle and atrium, and amelioration of secondary pulmonary hypertension, negative effects of CF-LVAD therapy on right ventricular filling and function, through right-sided loading and septal interaction, can make optimization challenging. Additionally, a lack of pulsatile energy provided by CF-LVAD therapy has physiologic consequences for end-organ function and may be responsible for a series of adverse effects. Rheological effects of intravascular pumps, especially shear stress exposure, result in platelet activation and hemolysis, which may result in both thrombotic and hemorrhagic consequences. Development of novel solutions for untoward device-circulatory interactions will facilitate hemodynamic support while mitigating adverse events. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.

Dynamic pressure-flow curve analysis of the native heart and left ventricular assist device for full and partial bypass conditions

BACKGROUND

During left ventricular assist device (LVAD) support, the external work performed by the native heart combines with the work performed by the rotary LVAD to provide cyclic flow through the LVAD and, in some conditions, through the aortic valve. In this study, a balance of external work was developed and validated for both full and partial bypass conditions that includes valve opening and aortic compliance.

METHODS

The theory assumes a steady-state contribution of external work from the rotary LVAD and a dynamic portion from the heart. Cyclic flow may be ejected through either the LVAD or ascending aorta, and an energy absorption term accounts for aortic compliance. Mock loop studies were performed for LV ejection fractions of 10%-28% combined with HeartMate II LVAD support at 8 and 11 krpm to produce a range of full and partial bypass conditions. The external work of the LVAD and native heart was computed from the experimental pressure-flow (H-Q) relations and compared to the theory.

RESULTS

Native heart contraction produces a counterclockwise loop in the pressure-flow relation of the LVAD which increased with ejection fraction, and during full bypass conditions the external work was preserved in the total systemic flow. During partial bypass conditions, forward flow through the ascending aorta was accompanied by a reversal during aortic valve closure resulting in a reduction in energy in the downstream flow.

CONCLUSIONS

The study presents a balance of external work during full and partial bypass LVAD support. Experimental data validated the additional terms corresponding to forward flow and aortic compliance that contribute to the system balance. This expanded theory can be applied to LVAD design and control to improve pulsatility and aortic valve biomechanics.

Left Ventricular Flow Dynamics with the HeartMate3 Left Ventricular Assist Device: Effect of Inflow Cannula Position and Speed Modulation

Improper left ventricular assist device (LVAD) inflow cannula (IC) positioning creates areas of stasis and low pulsatility that predispose thromboembolism, but may be mitigated with LVAD speed modulation. A mock loop study was performed to assess the sensitivity of left ventricle (LV) flow architecture to IC position and speed modulation during HeartMate3 support. System pressure, flow, and the time-resolved velocity field were measured within a transparent silicone LV for three IC angles and three IC insertion depths at matched levels of cardiac function and LVAD speed. Inflow cannula angulation towards the septum increased the resistance to LVAD flow as well as increasing the size and energy of the counter-clockwise (CCW) vortex. Apical velocity was reduced compared to IC angulation towards the mitral valve, but regional pulsatility was maintained across all angles and LVAD speeds. Increased IC protrusion decreased LVAD flow resistance, increasing velocity within the IC but reducing flow and pulsatility in the adjacent apical region. Increasing LVAD flow resistance improves aortic valve opening and strengthens the CCW vortex which directs inflow towards the septum, producing higher blood residence time and shear activation potential. Despite this impact on flow architecture, pulsatility reduction with increased LVAD speed was minimal with the HeartMate3 speed modulation feature.

In-silico analysis of outflow graft implantation orientation and cerebral thromboembolism incidence for full LVAD support

We investigate tailoring cannula implantation angles of left ventricle assist devices (LVAD) to reduce cerebral embolism risk for full LVAD support. We resolve pulsatile hemodynamics with a multi-scale computational fluid dynamics model coupled to a Lagrangian scheme tracking 2-5 mm particles for three cannula implantations. Blood is modeled as non-Newtonian. Cerebral flow distribution is altered depending on anastomosis angle and comparison of means embolization rates between steady and unsteady flow models show that unsteady modeling is more accurate even in the full LVAD support case. Intermediate angle implantation yields lowest cerebral embolization incidence of 11% vs 29% for normal and 36% for shallow implantation.

Computational Fluid Dynamics Study of Cerebral Thromboembolism Risk in Ventricular Assist Device Patients: Effects of Pulsatility and Thrombus Origin

This study investigates the hypothesis that by surgically manipulating the outflow graft (OG) implantation during ventricle assist device placement, it may be possible to reduce the risk of cerebral embolism. We investigate this hypothesis using a computational approach on a patient-specific basis under fully pulsatile hemodynamics with a multiscale computational fluid dynamics model incorporating a coupled Eulerian-Lagrangian scheme that effectively tracks emboli in the fluid domain. Blood is modeled as a non-Newtonian fluid based on the hematocrit level. Preliminary flow analysis shows that depending on the anastomosis angle the left ventricular assist device (LVAD) can enhance the flow to the cerebral circulation by nearly 31%. Z-test results suggest that unsteady-flow modeling ought to be an integral part of any cardiovascular simulation with residual ventricular function. Assuming unsteady-flow conditions, a shallow LVAD outflow graft anastomosis angle is the most optimal if thrombi are released from the aortic-root reducing cerebral embolization incidence to 15.5% and from the ventricle to 17%, while a more pronounced anastomosis angle becomes advantageous when particles originate from the LVAD with an embolization rate of 16.9%. Overall, computations suggest that a pronounced LVAD anastomosis angle is the better implementation. Unsteady modeling is shown to be necessary for the presence of significant antegrade aortic-root flow which induces cyclical flow patterns due to residual pulsatility. On the other hand, depending on thrombus origin and ventricular assist devices (VAD) anastomosis angle there is a strong tradeoff in embolization rates.

How well do we understand pulsatility in the context of modern ventricular assist devices?

BACKGROUND

Modern ventricular assist devices (VADs) use a continuous flow design. It has been suggested that a lack of pulsatility contributes to a range of adverse outcomes including pump thrombus, gastrointestinal bleeding and stroke. To better assess the role of pulsatility in these adverse events, we first require a clear definition of 'pulsatility' in the setting of a severely impaired ventricle and a modern continuous flow VAD.

METHODS

A literature review was conducted to elucidate the understanding of pulsatility in modern VAD literature. Search engines used included PUBMED, EMBASE and the Cochrane library. Articles were appraised on three aspects: Whether they mentioned pulsatility; whether they mentioned which pulsatility measure was used and finally which methodology was used to obtain the value.

RESULTS

Of 354 articles reviewed, only 13 met our broad inclusion criteria. Of these articles, the most cited measure was pulsatility index (PI) - used by 11 of the publications. The methodology used to obtain the value was not uniform and five articles did not clearly state it. Other measures included pulse pressure and surplus haemodynamic energy. The majority of articles did not directly discuss pulsatility in the setting of patient-pump interaction.

CONCLUSION

Most publications did not provide a definition for pulsatility. In those that did, the most common measure was PI. Measuring PI was not standardised. Few papers addressed the impact of intrinsic ventricular function and arterial compliance on pulsatility. We suggest that future publications adopt a uniform definition which encompasses both patient and pump characteristics.

Assessment of ocular blood flow in continuous-flow ventricular assist device by laser speckle flowgraphy

Although the influence of continuous-flow left ventricular assist device (CF-LVAD) support on peripheral circulation has been widely discussed, its monitoring modalities are limited. The aim of this study was to assess the peripheral circulation using the laser speckle flowgraph (LSFG) which can quantitatively measure the ocular blood flow. We implanted a centrifugal CF-LVAD (EVAHEART^®; Sun Medical Technology Research Corporation, Nagano, Japan) in five adult goats (body weight 44.5 ± 2.9 kg) under general anesthesia. The waveform of the central retinal artery using the mean blur rate (MBR) for ocular blood velocity and fluctuations as a parameter of pulsatility were obtained before LVAD implantation and after LVAD full-bypass support. The MBR waveform and LSFG fluctuation data were compared with the waveform and pulsatility index of the external carotid artery using an ultrasonic flow meter to evaluate circulatory patterns at different levels. The MBR waveform pattern of the central retinal artery was pulsatile before LVAD implantation and less pulsatile under LVAD full bypass. The fluctuation was 14.7 ± 1.86 before LVAD implantation and 3.85 ± 0.61 under LVAD full bypass (p < 0.01), respectively. The fluctuations of LSFG showed a strong correlation with the pulsatility index of the external carotid artery meaning that similar changes in circulatory pattern were observed at two different levels. Measuring the ocular blood flow using LSFG has potential utility for the assessment of the status of the peripheral circulation and its pulsatility during CF-LVAD.

Comparison of Hemodynamic Energy between Expanded Polytetrafluoroethylene and Dacron Artificial Vessels

Background

Artificial grafts such as polyethylene terephthalate (Dacron) and expanded polytetrafluoroethylene (ePTFE) are used for various cardiovascular surgical procedures. The compliance properties of prosthetic grafts could affect hemodynamic energy, which can be measured using the energy-equivalent pressure (EEP) and surplus hemodynamic energy (SHE). We investigated changes in the hemodynamic energy of prosthetic grafts.

Methods

In a simulation test, the changes in EEP for these grafts were estimated using COMSOL MULTIPHYSICS. The Young modulus, Poisson ratio, and density were used to analyze the grafts’ material properties, and pre- and post-graft EEP values were obtained by computing the product of the pressure and velocity. In an in vivo study, Dacron and ePTFE grafts were anastomosed in an end-to-side fashion on the descending thoracic aorta of swine. The pulsatile pump flow was fixed at 2 L/min. Real-time flow and pressure were measured at the distal part of each graft, while clamping the other graft and the descending thoracic aorta. EEP and SHE were calculated and compared.

Results

In the simulation test, the mean arterial pressure decreased by 39% for all simulations. EEP decreased by 42% for both grafts, and by around 55% for the native blood vessels after grafting. The in vivo test showed no significant difference between both grafts in terms of EEP and SHE.

Conclusion

The post-graft hemodynamic energy was not different between the Dacron and ePTFE grafts. Artificial grafts are less compliant than native blood vessels; however, they can deliver pulsatile blood flow and hemodynamic energy without any significant energy loss.

Targeting Peripheral Vascular Pulsatility in Heart Failure Patients with Continuous-Flow Left Ventricular Assist Devices: The Impact of Pump Speed

Current continuous-flow left ventricular assist devices (LVADs) decrease peripheral vascular pulsatility, which may contribute to side effects such as bleeding and thrombotic events. However, the actual impact of manipulating LVAD pump speed, revolutions per minute (rpm), on peripheral (brachial) pulsatility index (brachial PI), in patients with heart failure implanted with a HeartWare (HVAD) or HeartMateII (HMII) LVAD is unknown. Therefore, blood velocities (Doppler ultrasound) in the brachial artery were recorded and brachial PI calculated across rpm manipulations which spanned the acceptable clinical outpatient range: 360 rpm (HVAD, n = 10) and 1200 rpm (HMII, n = 10). Left ventricular assist device-derived PIs were also recorded: HVAD maximal blood flow (HVADV max), HVAD minimum blood flow (HVADV min), and HMII PI (HMIIPI). Brachial PI changed significantly with rpm manipulations, from 2.3 ± 0.6 to 4.1 ± 0.8 (HVAD) and from 1.8 ± 0.5 to 3.6 ± 1.0 (HMII). Multilevel linear modeling with random intercepts revealed a 180 rpm decrease of the HVAD resulted in a 0.9 ± 0.1 (37 ± 4%, d = 2.65) increase in brachial PI and a 600 rpm decrease in the HMII resulted in a 0.8 ± 0.1 (38 ± 3%, d = 4.66) increase. Furthermore, a reduction in rpm resulted in a 20.0 ± 0.3% power savings, and a reduction in device reported blood flow of 9 ± 1%. Brachial PI was linearly related to HVADV max, HVADV min, their difference (R = 0.42, R = 0.65, and R = 0.54, respectively), and HMIIPI (R = 0.86). Manipulating LVAD pump speed, within a clinically acceptable outpatient range, resulted in a significant change in brachial PI, which was reflected by pump indices, documenting the potential for LVAD pump speed manipulations to improve LVAD outcomes.

An advanced universal circulatory assist device for left and right ventricular support: First report of an acute in vivo implant

Background

The Advanced ventricular assist device (Advanced VAD) is designed as a universal pump intended to prevent backflow in the event of pump stoppage, to maintain physiological pulse pressure, and to be used as both a left and right VAD. The purpose of this study was to evaluate the performance of the Advanced VAD as both a left and right VAD in an acute in vivo study in calves.

Methods

The Advanced VAD was implanted through a median sternotomy in 5 healthy calves (weight, 71.4-91.2 kg) as a left VAD (n = 3) or a right VAD (n = 2). After implantation, hemodynamic parameters, including general performance and pump stoppage, were evaluated.

Results

The Advanced VAD was successfully implanted as a left and right VAD without cardiopulmonary bypass. The speed range of the Advanced VAD was 2500 to 3500 rpm as a left VAD and 2000 to 2500 rpm as a right VAD. Up to 4.3 L/min was achieved for both left and right VAD configurations. To demonstrate the automatic shut-off feature, the pump was stopped without clamping the outflow graft. The outflow graft was then clamped, which produced no significant changes in the arterial pressure waveform. The pulse pressures under the left VAD configuration were 38 mm Hg, 17 mm Hg, 14 mm Hg, and 16 mm Hg at baseline, 2500 rpm, 3000 rpm, and 3500 rpm, respectively.

Conclusions

This acute in vivo study demonstrated the pump performance, anatomical fitting as both left VAD and right VAD, and regurgitant flow shut-off feature of the Advanced VAD.

Hemodynamic performance of a compact centrifugal left ventricular assist device with fully magnetic levitation under pulsatile operation: An in vitro study

Long-term using continuous flow ventricular assist devices could trigger complications associated with diminished pulsatility, such as valve insufficiency and gastrointestinal bleeding. One feasible solution is to produce pulsatile flow assist with speed regulation in continuous flow ventricular assist devices. A third-generation blood pump with pulsatile operation control algorithm was first characterized alone under pulsatile mode at various speeds, amplitudes, and waveforms. The pump was then incorporated in a Mock circulation system to evaluate in vitro hemodynamic effects when using continuous and different pulsatile operations. Pulsatility was evaluated by surplus hemodynamic energy. Results showed that pulsatile operations provided sufficient hemodynamic assistance and increased pulsatility of the circulatory system (53% increment), the mean aortic pressure (65% increment), and cardiac output (27% increment). The pulsatility of the system under pulsatile operation support was increased 147% compared with continuous operation support. The hemodynamic performance of pulsatile operations is susceptible to phase shifts, which could be a tacking angle for physiological control optimization. This study found third-generation blood pumps using different pulsatile operations for ventricular assistance promising.

Evaluation of clinically relevant operating conditions for left ventricular assist device investigations

Standardized boundary conditions for flow rate and pressure difference are currently not available for the development and certification process of ventricular assist devices. Thus, interdisciplinary studies lack comparability and quantitative assessment. Universally valid boundary conditions could be used for the application of numerical and experimental investigations and the approval procedure of ventricular assist devices. In order to define such boundaries, physiological data from INCOR^® patients were evaluated. A total of 599 out of possible 627 ventricular assist device patients were analyzed regarding their cardiac demands of flow rate and pressure head. An analysis of long-term data was performed, in order to provide respective, static mean values for benchmark testing. Furthermore, the short-term data of 188 patients delivered field data-based dynamic flow and pressure curves. The results of the study revealed physiologically reasonable boundary conditions, which can be applied in numerical or experimental investigations of ventricular assist devices. For steady flow analysis, single values for flow rate (4.46 L/min) and pressure head (62 mmHg) are suggested. For the support of pulsatile and unsteady flow studies, seven typical patients and one representative dynamic curve for flow rate and pressure head are proposed.The standardized results provided in this article, can be used in favor of interdisciplinary comparability of future numerical computations or in vitro ventricular assist device tests in research, development, and approval.

Quantification of Pulsed Operation of Rotary Left Ventricular Assist Devices with Wave Intensity Analysis

The current generation of left ventricular assist devices (LVADs) provides continuous flow and has the capacity to reduce aortic pulsatility, which may be related to a range of complications associated with these devices. Pulsed LVAD operation using speed modulation presents a mechanism to restore aortic pulsatility and potentially mitigate complications. We sought to investigate the interaction of axial and centrifugal LVADs with the LV and quantify the effects of continuous and pulsed LVAD operations on LV generated wave patterns under different physiologic conditions using wave intensity analysis (WIA) method. The axial LVAD created greater wave intensity associated with LV relaxation. In both LVADs, there were only minor and variable differences between the continuous and pulsed operations. The response to physiologic stress was preserved with LVAD implantation as wave intensity increased marginally with volume loading and significantly with infusion of norepinephrine. Our findings and a new approach of investigating aortic wave patterns based on WIA are expected to provide useful clinical insights to determine the ideal operation of LVADs.

In vitro performance of trans-valve left ventricular assist device installed at aortic valve position

In this study, we developed a trans-valve left ventricular assist device (LVAD) that unites a rear-impeller axial-flow blood pump (AFBP) and a polymer membrane valve placed at the aortic valve position. The diameter and length of the rear impeller AFBP was 12 and 63 mm, respectively. The polymer membrane valve was similar to the jelly-fish valve consisting of a valve leaflet made of silicone rubber (thickness 0.5 mm), valve ring (diameter: 25 mm), and valve spokes. The trans-valve LVAD was examined in a mock circulation. An implantable pulsatile flow (PF) VAD was connected to an atrial reservoir to simulate the left ventricle (LV), and the Hall valve was worn in the inflow port, and the trans-valve LVAD was placed in the outflow port as an outflow valve. When the motor rotational speed increased to 26 400 rpm, the mean aortic flow increased from 4.2 to 5.3 L/min, mean aortic pressure increased from 83.4 to 100 mm Hg, and mean motor current of the implantable PF VAD decreased from 1.18 to 0.94 A (unloading effect on LV -21%). The energy equivalent pressure increased from 85.2 to 102 mm Hg, and surplus hemodynamic energy (SHE) decreased by -15.4% from the baseline. In conclusion, the trans-valve LVAD has an advantage of preserving pulsatility without any complicated mechanism and is a novel and promising LV support device.

The Effect of Inflow Cannula Angle on the Intraventricular Flow Field of the Left Ventricular Assist Device-Assisted Heart: An In Vitro Flow Visualization Study

Previous studies have identified left ventricular assist device (LVAD) inflow cannula (IC) malposition as a significant risk for pump thrombosis. Thrombus development is a consequence of altered flow dynamics, which can produce areas of flow stasis or high shear that promote coagulation. The goal of this study was to measure the effect of IC orientation on the left ventricle (LV) flow field using a mock circulatory loop, and identify flow-based indices that are sensitive measures of cannula malposition. Experimental studies were performed with a customized silicone model of the dilated LV and the EVAHEART Centrifugal LVAS (Evaheart, Inc.; Houston TX). The velocity field of the LV midplane was measured for a transparent IC oriented parallel to and rotated 15° toward the septum under matched hemodynamic conditions. Vortex structures were analyzed and localized stasis calculated within the IC and combined with a map of normalized pulsatile velocity. The velocity fields revealed increased apical stasis and lower pulsatility with a small angulation of the IC. A significant change in vortex dynamics with the angled IC was observed, doubling the size of the counterclockwise (CCW) vortex while reducing the kinetic energy provided by LVAD support. A significant decrease in average and systolic velocities within the IC was found with cannula angulation, suggesting an increased resistance that affects primarily systolic flow and is worsened with increased LVAD support. These common echocardiographic indices offer the opportunity for immediate clinical application during ramp study assessment. Optimized IC positioning may be determined preoperatively using imaging techniques to develop patient-specific surgical recommendations.

PulseCath iVAC2L: next-generation pulsatile mechanical circulatory support

Contemporary state of the art percutaneous coronary intervention techniques offer treatment strategies and solutions to an increasing number of patients with heart failure and complex coronary artery disease. Percutaneous mechanical circulatory support is intended to alleviate the mechanical and energetic workload imposed to a failing ventricle by reducing left ventricle pressures and volumes and potentially also increasing coronary blood flow. The PulseCath iVAC2L is a transaortic left ventricular assist device that applies a pneumatic driving system to produce pulsatile forward flow. Herein, the essential aspects regarding iVAC2L are discussed with focus on its mechanisms of action and the available clinical experience.

The design modification of advanced ventricular assist device to enhance pulse augmentation and regurgitant flow shut-off

The new Advanced ventricular assist device (Advanced VAD) has many features such as improving pulsatility and preventing regurgitant flow during pump stoppage. The purpose of this study was to evaluate the effects of design modifications of the Advanced VAD on these features in vitro. Bench testing of four versions of the Advanced VAD was performed on a static or pulsatile mock loop with a pneumatic device. After pump performance was evaluated, each pump was run at 3000 rpm to evaluate pulse augmentation, then was stopped to assess regurgitant flow through the pump. There was no significant difference in pump performance between the pump models. The average pulse pressure in the pulsatile mock loop was 23.0, 34.0, 39.3, 33.8, and 37.3 mm Hg without pump, with AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. The pulse augmentation factor was 48%, 71%, 47%, and 62% with AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. In the pump stop test, regurgitant flow was -0.60 ± 0.70, -0.13 ± 0.57, -0.14 ± 0.09, and -0.18 ± 0.06 L/min in AV010, AV020 3S, AV020 6S, and AV020 RC, respectively. In conclusion, by modifying the design of the Advanced VAD, we successfully showed the improved pulsatility augmentation and regurgitant flow shut-off features.

COMPARISON OF THREE CONTROL STRATEGIES FOR AXIAL BLOOD PUMP

Facing the gradually increased prevalence of heart failure (HF) and the shortage of donated hearts, the blood pump is widely used to prolong the life of end-stage HF patients: however, the pump generates continuous flow under constant rotational speed, declining the arterial pulsatility and causing related complications. Previous studies show that synchronous copulsation might be the best control strategy for restoring pulsatility, but synchronous strategies are needed to monitor the phase of the heartbeat, which will make the controller complex and impair its robustness. Here, we compare constant speed, synchronous copulsation in a model of a cardiovascular system with a blood pump, which shows that copulsation offers more arterial pulsatility, less pump power-consumption, and thus better battery endurance, and constant speed offers a greater ventricular unloading effect. Meanwhile, we design a strategy based on transforming left ventricular pressure, which is easier to implement and has similar effect to synchronous copulsation.

A Proof-of-Concept Demonstration for a Novel Soft Ventricular Assist Device

Patients treated by current ventricular assist devices (VADs) suffer from various post implantation complications including gastrointestinal bleeding and arteriovenous malformation. These issues are related to intrinsically mismatch of generated flow by VADs and the physiological flow. In addition, the common primary drawback of available VADs is excessive surgical dissection during implantation, which limits these devices to less morbid patients. We investigated an alternative soft VAD (SVAD) system that generates physiological flow, and designed to be implanted using minimally invasive surgery by leveraging soft materials. A soft VAD (which is an application of intraventricular balloon pump) is developed by utilizing a polyurethane balloon, which generates pulsatile flow by displacing volume within the left ventricle during its inflation and deflation phases. Our results show that the SVAD system generates an average ejection fraction of 50.18 ± 1.52% (n = 6 ± SD) in explanted porcine hearts. Since the SVAD is implanted via the apex of the heart, only a minithoracotomy should be required for implantation. Our results suggest that the SVAD system has the performance characteristics that could potentially make it useful for patients in acute and/or chronic heart failure, thus serving as a bridge-to-transplantation or bridge-to-recovery.

Blood damage in Left Ventricular Assist Devices: Pump thrombosis or system thrombosis?

Introduction:

Despite significant technical advancements in the design and manufacture of Left Ventricular Assist Devices, post-implant thrombotic and thromboembolic complications continue to affect long-term outcomes. Previous efforts, aimed at optimizing pump design as a means of reducing supraphysiologic shear stresses generated within the pump and associated prothrombotic shear-mediated platelet injury, have only partially altered the device hemocompatibility.

Methods:

We examined hemodynamic mechanisms that synergize with hypershear within the pump to contribute to the thrombogenic potential of the overall Left Ventricular Assist Device system.

Results:

Numerical simulations of blood flow in differing regions of the Left Ventricular Assist Device system, that is the diseased native left ventricle, the pump inflow cannula, the impeller, the outflow graft and the anastomosed downstream aorta, reveal that prothrombotic hemodynamic conditions might occur at these specific sites. Furthermore, we show that beyond hypershear, additional hemodynamic abnormalities exist within the pump, which may elicit platelet activation, such as recirculation zones and stagnant platelet trajectories. We also provide evidences that particular Left Ventricular Assist Device implantation configurations and specific post-implant patient management strategies, such as those allowing aortic valve opening, are more hemodynamically favorable and reduce the thrombotic risk.

Conclusion:

We extend the perspective of pump thrombosis secondary to the supraphysiologic shear stress environment of the pump to one of Left Ventricular Assist Device system thrombosis, raising the importance of comprehensive characterization of the different prothrombotic risk factors of the total system as the target to achieve enhanced hemocompatibility and improved clinical outcomes.

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.

Protracted aortic valve closure during peripheral veno-arterial extracorporeal life support: is intra-aortic balloon pump an effective solution?

Background:

Left ventricular (LV) afterload increase with protracted aortic valve (AV) closure may represent a complication of veno-arterial extracorporeal membrane oxygenation (V-A ECMO). The aim of the present study was to assess the effects of an intra-aortic balloon pump (IABP) to overcome such a hemodynamic shortcoming in patients submitted to peripheral V-A ECMO.

Methods:

Among 184 adult patients who were treated with peripheral V-A ECMO support at Medical University Center Maastricht Hospital between 2007 and 2018, patients submitted to IABP implant for protracted AV closure after V-A ECMO implant were retrospectively identified. All clinical and hemodynamic data, including echocardiographic monitoring, were collected and analyzed.

Results:

During the study period, 10 subjects (mean age 60 years old, 80% males) underwent IABP implant after peripheral V-A ECMO positioning due to the diagnosis of protracted AV closure and inefficient LV unloading as assessed by echocardiography and an absence of pulsation in the arterial pressure wave.

Recovery of blood pressure pulsatility and enhanced LV unloading were observed in 8 patients after IABP placement, with no significant differences in the main hemodynamic parameters, inotropic therapy or in the ECMO flow (p=0.48). The weaning rate in this patient subgroup (mean ECMO duration 8 days), however, was only 10%, with another patient finally transplanted, leading to a 20% survival-to-hospital discharge.

Conclusion:

IABP placement was an effective solution in order to reverse the protracted AV closure and impaired LV unloading observed during peripheral V-A ECMO support. However, the impact on the weaning rate and survival needs further investigations.

Effect of pulsatile flow perfusion on decellularization

Background

Decellularized animal organs have been used as scaffolds for tissue engineering. To make a properly functioning scaffolds, the extracellular matrix (ECM) components must be preserved after decellularization. Because pulsatile flow is known to be beneficial for tissue perfusion, pulsatile perfusion of a detergent might decrease the exposure time of the tissues to the detergent used for decellularization. Using Energy Equivalent Pressure (EEP) as a pulsatility parameter, the effect of pulsatile flow in decellularization process is studied.

Results

Twelve rat hearts were decellularization with 1% sodium dodecyl sulfate (SDS) solution for 2 h. They are divided into two groups, one with pulsatile perfusion (n = 6), the other with non-pulsatile perfusion (n = 6) of SDS. The initial mean perfusion pressures were same in both group. The result indicated that the EEP and the perfusion flow were increased significantly in the pulsatile group compared to the non-pulsatile group. Photographs taken during the decellularization showed more profound decellularization in the pulsatile group. The residual DNA content in the scaffolds was significantly lower in the pulsatile group. However, the level of ECM components, collagen and GAG showed no significant differences between the groups.

Conclusions

Decellularization is more efficient in pulsatile flow than in non-pulsatile flow but still preserves the ECM molecules.

Flow features and device-induced blood trauma in CF-VADs under a pulsatile blood flow condition: A CFD comparative study

In this study, the flow features and device-associated blood trauma in 4 clinical ventricular assist devices (VADs; 2 implantable axial VADs, 1 implantable centrifugal VAD, and 1 extracorporeal VAD) were computationally analyzed under clinically relevant pulsatile flow conditions. The 4 VADs were operated at fixed pump speed at a mean rate of 4.5 L/min. Mean pressure difference, wall shear stress, volume distribution of scalar shear stress (SSS), and shear-induced hemolysis index (HI) were derived from the flow field of each VAD and were compared. The computationally predicted mean pressure difference across the 3 implantable VADs was ~70 mmHg, and the extracorporeal VAD was ~345 mmHg, which matched well with their reported pressure-flow curves. The axial VADs had higher mean wall shear stress and SSS compared with the centrifugal VADs. However, the residence time of the centrifugal VADs was much longer compared with the axial VADs because of the large volume of the centrifugal VADs. The highest SSS was observed in one axial VAD, and the longest exposure time was observed in 1 centrifugal VAD. These 2 VADs generated the highest HI. The shear-induced HI varied as a function of flow rate within each cardiac cycle. At fixed pump speed, the HI was greatest at low flow rate due to longer exposure time to shear stress compared with at high flow rate. Subsequently, we hypothesize that to reduce the risk of blood trauma during VAD support, shear stress magnitude and exposure time need to be minimized.

Hemodynamic effects of synchronizing an intra-aortic VAD in reverse-rotation control with left ventricle: a mock loop study

The IntraVAD is an intra-aortic left ventricular assist device (LVAD) to be located in the ascending aorta. In order to enhance unloading and promote coronary flow for the left ventricle (LV), an operating mechanism, reverse-rotation control (RRc) mode, has been developed for the IntraVAD and tested in vitro in a mock circulation loop (MCL). The RRc mode consists of forward rotation (FR) and reverse rotation (RR). The synchronization between the IntraVAD and the LV was studied to offload the ventricle more effectively and to improve myocardial perfusion. The percentage time length of the FR period in the cardiac cycle (Tlf) and time offset between the central-lines of the FR period and the LV systole (Toc) are two parameters of the RRc mode that were varied to adjust the synchronization between the IntraVAD and the LV. The ejection fraction (EF), coronary perfusion pressure (CPP), and arterial pulsatility index (API) were measured at different Tlf and Toc values. These hemodynamic results closely correlated to the LV unloading, coronary perfusion, and peripheral arterial pulsatility. The EF, CPP and API were fed into a weighted normalized scalar (WNS) which was implemented to comprehensively evaluate the hemodynamic influence. The WNS result shows that the overall hemodynamic response is more sensitive to the changes in Toc value than Tlf value. The result shows a significant reduction in LV afterload by starting the FR before LV contraction, then switching to RR at the onset of ventricular dilation. The optimal phase shift of -π/5 was found to precede LV contraction, indicating that changes in LV afterload are more sensitive to the phase shift at the start of the ventricular systole than at the end. Thus, a phase advance between intra-aortic pumps and the LV is critical to unload the ventricle and promote myocardial recovery.

Effect of Outflow Graft Size on Flow in the Aortic Arch and Cerebral Blood Flow in Continuous Flow Pumps: Possible Relevance to Strokes

One of the most devastating complications of continuous flow left ventricular devices (CFLVADS) is stroke, with a higher incidence in HeartWare Ventricular Assist Device (HVAD) as compared with HEARTMATE II. The reason for the observed difference in stroke rates is unclear. Because outflow graft diameters are different, we hypothesized that this could contribute to the difference in stroke rates. A computational fluid-structure interaction model was created from the computed tomography (CT) scan of a patient. Pressures were used as the boundary condition and the flow through the cerebral vessels was derived as outputs. Flow into the innominate artery was very sensitive to the anastomosis angle for a 10 mm as compared with a 14 mm graft, with the net innominate flow severely compromised with a 10 mm graft at 45° angle. Aortic insufficiency seems to affect cerebral blood flow nonlinearly with an 80% decrease at certain angles of outflow graft anastomosis. Arterial return in to the arch through a narrow graft has important jet effects and results in significant flow perturbations in the aortic arch and cerebral vessels and stasis. A 10 mm graft is more sensitive to angle of insertion than a 14 mm graft. Under some conditions, serious hypoperfusion of the innominate artery is possible. Aortic incompetence results in significant decrease of cerebral blood flow. No stasis was found in the pulsatile flow compared with LVAD flow.

Mechanical Circulatory Support for Advanced Heart Failure: Are We about to Witness a New "Gold Standard"?

The impact of left ventricular assist devices (LVADs) for the treatment of advanced heart failure has played a significant role as a bridge to transplant and more recently as a long-term solution for non-eligible candidates. Continuous flow left ventricular assist devices (CF-LVADs), based on axial and centrifugal design, are currently the most popular devices in view of their smaller size, increased reliability and higher durability compared to pulsatile flow left ventricular assist devices (PF-LVADs). The trend towards their use is increasing. Therefore, it has become mandatory to understand the physics and the mathematics behind their mode of operation for appropriate device selection and simulation set up. For this purpose, this review covers some of these aspects. Although very successful and technologically advanced, they have been associated with complications such as pump thrombosis, haemolysis, aortic regurgitation, gastro-intestinal bleeding and arterio-venous malformations. There is perception that the reduced arterial pulsatility may be responsible for these complications. A flow modulation control approach is currently being investigated in order to generate pulsatility in rotary blood pumps. Thrombus formation remains the most feared complication that can affect clinical outcome. The development of a preoperative strategy aimed at the reduction of complications and patient-device suitability may be appropriate. Patient-specific modelling based on 3D reconstruction from CT-scan combined with computational fluid dynamic studies is an attractive solution in order to identify potential areas of stagnation or challenging anatomy that could be addressed to achieve the desired outcome. The HeartMate II (axial) and the HeartWare HVAD (centrifugal) rotary blood pumps have been now used worldwide with proven outcome. The HeartMate III (centrifugal) is now emerging as the new promising device with encouraging preliminary results. There are now enough pumps on the market: it is time to focus on the complications in order to achieve the full potential and selling-point of this type of technology for the treatment of the increasing heart failure patient population.

Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study

Background

BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta.

Material/Methods

Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode.

Results

The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode.

Conclusions

BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments.

Review Article: Comparison of perfusion modes on microcirculation during acute and chronic cardiac support: is there a difference?

Although heart-lung machines and cardiac assist devices have been used successfully for acute and chronic cardiac support for decades, controversies still remain concerning the benefits of pulsatile and non-pulsatile perfusion. The core of the debate is whether enough energy is generated by the artificial pulse to keep capillary beds open and cell metabolism stabilized during acute or chronic cardiac support. In other words, does artificial pulsatility exist in the microcirculation: small vessels of less than 100 μm in diameter? Many investigators have tried to use different tools and biomarkers to reflect directly or indirectly the state of the microcirculation when comparing the two different perfusion modes during acute and chronic cardiac support. However, the results are controversial. First, direct observation of the state of the microcirculation during acute and chronic cardiac support is limited; and reports concerning direct observation of the microcirculation with different perfusion modes in contemporary literature are rare. Secondly, different investigators have used their own criteria to define pulsatile flow. Therefore, it is necessary to develop more efficient methodologies, enabling direct observation of the microcirculation during acute and chronic cardiac support and also establish common criteria that will precisely quantify the pulsatile flow in terms of energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) levels. Using these critical parameters may explain how excess energy is created by pulsatile flow and maintains perfusion through the microcirculation by ensuring capillary patency. Perfusion (2007) 22, 115—119.