Hemolysis associated with Impella heart pump positioning: In vitro hemolysis testing and computational fluid dynamics modeling

Stroke outcomes following durable left ventricular assist device implant in patients bridged with micro-axial flow pump: Insights from a large registry

BACKGROUND

Stroke after durable left ventricular assist device (d-LVAD) implantation portends high mortality. The incidence of ischemic and hemorrhagic stroke and the impact on stroke outcomes of temporary mechanical circulatory support (tMCS) management among patients requiring bridge to d-LVAD with micro-axial flow-pump (mAFP, Abiomed) is unsettled.

METHODS

Consecutive patients, who underwent d-LVAD implantation after being bridged with mAFP at 19 institutions, were retrospectively included. The incidence of early ischemic and hemorrhagic stroke after d-LVAD implantation (<60 days) and association of pre-d-LVAD characteristics and peri-procedural management with a specific focus on tMCS strategies were studied.

RESULTS

Among 341 patients, who underwent d-LVAD implantation after mAFP implantation (male gender 83.6%, age 58 [48-65] years, mAFP 5.0/5.5 72.4%), the early ischemic stroke incidence was 10.8% and early hemorrhagic stroke 2.9%. The tMCS characteristics (type of mAFP device and access, support duration, upgrade from intra-aortic balloon pump, ECMELLA, ECMELLA at d-LVAD implantation, hemolysis, and bleeding) were not associated with ischemic stroke after d-LVAD implant. Conversely, the device model (mAFP 2.5/CP vs. mAFP 5.0/5.5: HR 5.6, 95%CI 1.4-22.7, p = 0.015), hemolysis on mAFP support (HR 10.5, 95% CI 1.3-85.3, p = 0.028) and ECMELLA at d-LVAD implantation (HR 5.0, 95% CI 1.4-18.7, p = 0.016) were associated with increased risk of hemorrhagic stroke after d-LVAD implantation. Both early ischemic (HR 2.7, 95% CI 1.9-4.5, p < 0.001) and hemorrhagic (HR 3.43, 95% CI 1.49-7.88, p = 0.004) stroke were associated with increased 1-year mortality.

CONCLUSIONS

Among patients undergoing d-LVAD implantation following mAFP support, tMCS characteristics do not impact ischemic stroke occurrence, while several factors are associated with hemorrhagic stroke suggesting a proactive treatment target to reduce this complication.

Cardiac Devices and Kidney Disease

A growing variety of cardiac devices are available to monitor or support cardiovascular function. The entwined nature of cardiovascular disease and kidney disease makes the relationship of these devices with kidney disease a multifaceted question relating to the use of these devices in individuals with kidney disease and to the effects of the devices and device placement on kidney health. Cardiac devices can be categorized broadly into cardiac implantable electronic devices, structural devices, and circulatory assist devices. Cardiac implantable electronic devices include devices for monitoring and managing cardiac electrical activity and devices for monitoring hemodynamics. Structural devices modify cardiac structure and include valve prostheses, valve repair clips, devices for treating atrial septal abnormalities, left atrial appendage closure devices, and interatrial shunt devices. Circulatory assist devices support the failing heart or support cardiac function during high-risk cardiac procedures. Evidence for the use of these devices in individuals with kidney disease, effects of the devices on kidney health and function, specific considerations with devices in kidney disease, and important knowledge gaps are surveyed in this article. With the growing prevalence of combined cardiorenal disease and the increasing variety of cardiac devices, kidney disease considerations are an important aspect of device therapy.

Numerical methods for hemolysis and thrombus evaluation in the percutaneous ventricular assist device

BACKGROUND

A percutaneous ventricular assist device (pVAD) is an effective method to treat heart failure, but its complications, mainly hemolysis and thrombus formation, cannot be ignored. Accurate evaluation of hemolysis and thrombus formation in pVAD is essential to guide the development of pVAD and reduce the incidence of complications.

METHODS

This study optimized the numerical model to predict hemolysis and thrombus formation in pVAD. The hemolysis model is based on the power law function, and the multi-component thrombus prediction model is improved by introducing the von Willebrand factor.

RESULTS

The error between the numerical simulation and the hydraulic performance experiment is within 5%. The numerical results of hemolysis are in good agreement with those of in vitro experiments. Meanwhile, the thrombus location predicted by the numerical model is the same as that found in the in vivo experiment.

CONCLUSION

The numerical model suggested in this study may therefore accurately assess the possible hemolytic and thrombotic dangers in pVAD, making it an effective tool to support the development of pVAD.

Cardiogenic Shock in Non-Ischemic Cardiomyopathy: Dynamic Mechanical Circulatory Support and Pathophysiology Illustration

Nonischemic cardiomyopathy (NICM) is a significant cause of cardiogenic shock (CS). We present a case of a 56-year-old previously healthy man who arrived with vague abdominal symptoms, over 2 weeks. Subsequently, the patient's condition rapidly deteriorated over 12 hours, leading to cardiogenic shock categorized as Society for Cardiovascular Angiography and Interventions (SCAI) stage D. Echocardiography and right heart catheterization confirmed multiorgan failure secondary to severe cardiac dysfunction. Mechanical circulatory support was initiated using an Impella CP device 20 hours after admission due to ongoing deterioration. Considering refractory cardiogenic shock and within 24 hours, the patient received combined veno-arterial extracorporeal membrane oxygenation (VA-ECMO) and Impella CP support (ECPElla). With gradual improvement in the patient's clinical status and organ function, successful weaning from VA ECMO to Impella 5.5 was achieved. Ultimately, the patient underwent a successful orthotopic heart and kidney transplantation, marking a significant milestone in his recovery. The case underscores the importance of promptly identifying and responding to cardiogenic shock through invasive hemodynamic assessment. Collaborative decision-making involving a multidisciplinary team played a crucial role in the initiation, escalation, and eventual weaning of mechanical circulatory support, culminating in the successful bridging to a dual organ transplantation for this patient with CS secondary to NICM.

Short-term percutaneous mechanical circulatory support: no promise without positioning!

Short-term percutaneous mechanical circulatory support by a micro-axial flow pump is increasingly used to support the left ventricle in cardiogenic shock. After a correct indication and placement, appropriate device management in the cardiac intensive care unit is vital to ensure optimal pump function and adequate haemodynamic support. A key element hereby is a correct percutaneous ventricular assist device (pVAD) position. This review explains how an optimal left-sided pVAD position can be achieved and maintained, focusing on the correct insertion depth and rotational angle. Useful imaging techniques, placement and replacement manoeuvres, and monitoring options through the console are discussed. The frequently encountered problem of mal-rotation towards the mitral valve, which may cause suction alarms, haemolysis, aortic regurgitation, and inadequate haemodynamic support, is explained. Finally, a practical bedside approach to assess pVAD position and discern suction alarms due to mal-positioning from haemodynamic problems is proposed.

In vitro comparative study of red blood cell and VWF damage on 3D printing biomaterials under different blood-contacting conditions

Mechanical circulatory support devices (MCSDs) are often associated with hemocompatible complications such as hemolysis and gastrointestinal bleeding when treating patients with end-stage heart failure. Shear stress and exposure time have been identified as the two most important mechanical factors causing blood damage. However, the materials of MCSDs may also induce blood damage when contacting with blood. In this study, the red blood cell and von Willebrand Factor (VWF) damage caused by four 3D printing biomaterials were investigated, including acrylic, PCISO, Somos EvoLVe 128, and stainless steel. A roller pump circulation experimental platform and a rotor blood-shearing experimental platform were constructed to mimic static and dynamic blood-contacting conditions of materials in MCSDs, respectively. Free hemoglobin assay and VWF molecular weight analysis were performed on the experimental blood samples. It indicated that different 3D printing materials and technology could induce different levels of damage to red blood cells and VWF, with acrylic causing the least damage under both static and dynamic conditions. In addition, it was found that blood damage measured for the same material differed on the two platforms. Therefore, a combination of static and dynamic experiments should be used to comprehensively investigate the effects of blood damage caused by the material. It can provide a reference for the design and evaluation of materials in different components of MCSDs.

Management of Bleeding and Hemolysis During Percutaneous Microaxial Flow Pump Support: A Practical Approach

Percutaneous ventricular assist devices (pVADs) are increasingly being used because of improved experience and availability. The Impella (Abiomed), a percutaneous microaxial, continuous-flow, short-term ventricular assist device, requires meticulous postimplantation management to avoid the 2 most frequent complications, namely, bleeding and hemolysis. A standardized approach to the prevention, detection, and treatment of these complications is mandatory to improve outcomes. The risk for hemolysis is mostly influenced by pump instability, resulting from patient- or device-related factors. Upfront echocardiographic assessment, frequent monitoring, and prompt intervention are essential. The precarious hemostatic balance during pVAD support results from the combination of a procoagulant state, due to critical illness and contact pathway activation, together with a variety of factors aggravating bleeding risk. Preventive strategies and appropriate management, adapted to the impact of the bleeding, are crucial. This review offers a guide to physicians to tackle these device-related complications in this critically ill pVAD-supported patient population.

Impella devices: a comprehensive review of their development, use, and impact on cardiogenic shock and high-risk percutaneous coronary intervention

INTRODUCTION

Impella devices have emerged as a critical tool for temporary mechanical circulatory support (TMCS) in the management of cardiogenic shock (CS) and high-risk percutaneous coronary interventions (PCI). The purpose of this review is to examine the history of the different Impella devices, their hemodynamic profiles, and how the data supports their use.

AREAS COVERED

This review covers the development and specifications of the Impella 2.5, Impella CP, Impella 5.0/Left Direct (LD), Impella RP, and Impella 5.5 devices. This review also covers the clinical trials that illuminate the Impella devices' use in their appropriate clinical contexts. These studies examine the effectiveness of Impella devices and have begun to yield promising results, demonstrating improved survival rates when compared to the historically high mortality rates associated with CS. It is important to weigh the benefits of Impella devices in light of their contraindications. A literature search was conducted by searching the PubMed database for reviews, meta-analyses, and clinical trials pertinent to Impella devices.

EXPERT OPINION

Impella devices are a crucial tool for management of patients undergoing high-risk PCI and those with CS. There is evidence that early Impella implantation is beneficial in the treatment of patients presenting with CS. Further randomized controlled trials are needed to better elucidate the benefits of Impella devices in various clinical settings.

Three-year experience of catheter-based micro-axial left ventricular assist device, Impella, in Japanese patients: the first interim analysis of Japan registry for percutaneous ventricular assist device (J-PVAD)

Catheter-based micro-axial ventricular assist device Impella® (Abiomed, Danvers, MA) has been used in Japanese patients with drug-refractory acute heart failure (AHF) since 2017. This is the first interim analysis of the ongoing Japan Registry for Percutaneous Ventricular Assist Device (J-PVAD) to investigate the safety and efficacy of Impella support. Between October 2017 and January 2020, 823 Japanese patients, who were treated with the Impella 2.5, CP, or 5.0 pump, were enrolled. The primary endpoints were safety profiles and cumulative 30-day survival. Among them, 44.8% of patients were acute myocardial infarction with cardiogenic shock. The Impella pumps were unable to implant in 4 patients. The Impella 2.5, CP, and 5.0 pumps were used in 72.4%, 6.2%, and 16.6%, respectively, and mean support duration was 8.1 ± 10.2 days. Combination use of Impella and venoarterial extracorporeal membrane oxygenation (VA-ECMO) was applied for 387 patients (47.3%). Pump stop occurred 22 patients (2.7%). Major adverse events included hemolysis (11.2%), hemorrhage/hematoma (6.1%), peripheral ischemia (1.6%), and stroke (1.6%). The overall 30-day survival was 62.2%. Survival of patients with single Impella support was significantly higher than patients with Impella combined with VA-ECMO support (81.1% vs 49.6%; p < 0.01), who had lower blood pressure, lower left ventricular ejection fraction, and higher degree of inotropic support. Results suggest that short-term outcome of Impella support for Japanese patients was favorable with acceptable safety profiles.

Mock circulatory loop applications for testing cardiovascular assist devices and in vitro studies

The mock circulatory loop (MCL) is an in vitro experimental system that can provide continuous pulsatile flows and simulate different physiological or pathological parameters of the human circulation system. It is of great significance for testing cardiovascular assist device (CAD), which is a type of clinical instrument used to treat cardiovascular disease and alleviate the dilemma of insufficient donor hearts. The MCL installed with different types of CADs can simulate specific conditions of clinical surgery for evaluating the effectiveness and reliability of those CADs under the repeated performance tests and reliability tests. Also, patient-specific cardiovascular models can be employed in the circulation of MCL for targeted pathological study associated with hemodynamics. Therefore, The MCL system has various combinations of different functional units according to its richful applications, which are comprehensively reviewed in the current work. Four types of CADs including prosthetic heart valve (PHV), ventricular assist device (VAD), total artificial heart (TAH) and intra-aortic balloon pump (IABP) applied in MCL experiments are documented and compared in detail. Moreover, MCLs with more complicated structures for achieving advanced functions are further introduced, such as MCL for the pediatric application, MCL with anatomical phantoms and MCL synchronizing multiple circulation systems. By reviewing the constructions and functions of available MCLs, the features of MCLs for different applications are summarized, and directions of developing the MCLs are suggested.

Surgically Implanted Impella Device for Patients on Impella CP Support Experiencing Refractory Hemolysis

The Impella CP (Abiomed Inc., Danvers, MA) is widely used in cardiac catheterization laboratories for patients presenting with cardiogenic shock, but it is also known to cause significant hemolysis. The risk of hemolysis can be reduced by properly positioning the device, ensuring an adequate volume status, and using full anticoagulation strategies; however, in some cases hemolysis persists. We present a case series of eight patients that were diagnosed with cardiogenic shock, underwent Impella CP placement, and then suffered from refractory hemolysis which was treated by upgrading the Impella device to the 5.0 or 5.5 version. Fifty percent (4/8) of the patients in this series were already receiving continuous renal replacement therapy, and the levels of plasma free hemoglobin (pFHb) and lactate dehydrogenase continued to increase after the implantation of the Impella CP. The median time between Impella CP placement and the diagnosis of refractory hemolysis was 16.5 hours (interquartile range [IQR], 8.0-26.0). The median time between the diagnosis of hemolysis to Impella upgrade was 6.0 hours (IQR, 4.0-7.0). A total of 87.5% (7/8) of patients experienced a drop in pFHb to below 40 mg/dl at 72 hours post-Impella upgrade, and they were discharged without any further need of dialysis. One patient expired due to irreversible multiple organ failure. We propose that early identification of hemolysis by close monitoring of pFHb and upgrading to the Impella 5.5 reduces hemolysis, prevents further kidney damage, and significantly improves clinical outcomes.

Multi-indicator analysis of mechanical blood damage with five clinical ventricular assist devices

PURPOSE

Device-induced blood damage contributes the hemolysis, thrombosis and bleeding complications in patients supported with ventricular assist device (VAD). This study aims to use a multi-indicator method to understand how devices causes blood damage and identify the "hot spots" of blood trauma within VADs.

METHODS

Computational fluid dynamics (CFD) methods were chosen to investigate the hemodynamic features of five clinical VADs (Impella 5.0, UltraMag, CHVAD, HVAD, and HeartMate II) under the same clinical support condition (flow rate of 4.5L/min, pressure head around 75 mmHg). A comprehensive multi-indicator evaluation method including hemodynamic parameters, hemolysis model, thrombotic potential model and bleeding probability model was used to analyze blood damage and assess the hemodynamic performance and hemocompatibility of these VADs.

RESULTS

Simulation results show that shear stress from 50 Pa to 100 Pa plays a major role in blood damage in Impella 5.0, UltraMag and CHVAD, while blood damage in HVAD and HeartMate II is mainly caused by shear stress greater than 100 Pa. Residence time was not the main factor for blood damage in Impella 5.0, and also makes a limited contribution to blood trauma in UltraMag and CHVAD, while it takes a critical role in elevating thrombotic potential in HVAD and HeartMate II. The distribution of regions of high hemolysis risk and high bleeding probability was similar for all these VADs and partially overlapped for high thrombotic potential regions. For Impella 5.0, regions with high hemolysis and bleeding risk were found mainly in the blade tip clearance and diffuser domains, high thrombotic potential regions were almost absent. For UltraMag, regions with high hemolysis, bleeding and thrombosis potential were found in two corners of the inlet pipe, the secondary flow passage, and the impeller eye. For CHVAD, the high-risk regions for hemolysis, bleeding and thrombosis are mainly in the inner side of the secondary flow passage and the middle region of the impeller passage. The narrow hydrodynamic clearance and impeller passage had a high risk of hemolysis and bleeding, and the clearance between the rotor and guide cone and the hydrodynamic clearance had high thrombotic potential. For HeartMate II, regions of high hemolysis risk and bleeding probability were found in the near-wall region of the straightener, the blade tip clearance and the diffuser domain. The corners of the inlet and outlet pipe and the straightener and diffuser regions had high thrombotic potential.

CONCLUSION

The risk of hemolysis, bleeding and thrombosis for these five VADs, in increasing order, was Impella 5.0, UltraMag, CHVAD, HVAD, and HeartMate II. Flow losses caused by the rotor mechanical movement, chaotic flow and narrow clearances increase the blood damage for all these VADs. The multi-indicator analysis can comprehensively evaluate the VAD performance with improved assessment accuracy of CFD.

Hemolysis during short-term mechanical circulatory support: from pathophysiology to diagnosis and treatment

INTRODUCTION

Despite advances in heart failure therapies and percutaneous coronary interventions, survival for cardiogenic shock remains poor. Percutaneous ventricular assist devices (pVAD) are increasingly used, but current evidence remains conflicting. The Impella is an example of such a device, based on a catheter mounted micro-axial continuous flow pump, that has been rapidly adopted in routine practice. An important aspect in the post implantation care is the prevention of complications. Hemolysis is one of the more frequent complications seen with this device.

AREAS COVERED

In this review we discuss the pathophysiology, diagnosis and treatment of hemolysis in patients supported with a pVAD. A practical algorithm for rapid identification of hemolysis and the underlying cause is presented, allowing for early treatment and prevention of further complications.

EXPERT OPINION

Hemolysis remains a threat to patients supported with any mechanical circulatory support device. Prevention as well as treatment demands for sufficient knowledge about the device, the optimal position and hemodynamics. Future studies should try to clarify some of the elements that are still unclear such as optimal anticoagulation, the place of pentoxyfilline or extracorporeal removal of free hemoglobin. This could help to optimize outcomes in clinical practice as well as future studies.

Anticoagulation for Percutaneous Ventricular Assist Device-Supported Cardiogenic Shock: JACC Review Topic of the Week

Interest in the use of mechanical circulatory support for patients presenting with cardiogenic shock is growing rapidly. The Impella (Abiomed Inc), a microaxial, continuous-flow, short-term, ventricular assist device (VAD), requires meticulous postimplantation management. Because systemic anticoagulation is needed to prevent pump thrombosis, patients are exposed to increased bleeding risk, further aggravated by sepsis, thrombocytopenia, and high shear stress-induced acquired von Willebrand syndrome. The precarious balance between bleeding and thrombosis in percutaneous VAD-supported cardiogenic shock patients is often the main reason that patient outcomes are jeopardized, and there is a lack of data addressing optimal anticoagulation management strategies during percutaneous VAD support. Here, we present a parallel anti-Factor Xa/activated partial thromboplastin time-guided anticoagulation algorithm and discuss pitfalls of heparin monitoring in critically ill patients. This review will guide physicians toward a more standardized (anti)coagulation approach to tackle device-related morbidity and mortality in this critically ill patient group.

Pulmonary Artery Pulsatility Index and Hemolysis during Impella-Incorporated Mechanical Circulatory Support

Background: Impella is a percutaneous transcatheter left ventricular assist device. Device-related hemolysis is a serious complication that is sometimes encountered depending on the device position, device speed, and support duration. However, the impact of hemodynamics on the occurrence of hemolysis remains unknown. In this study, we aimed to clarify the relationships between hemodynamics, especially right ventricular function, and the occurrence of hemolysis during Impella-incorporated mechanical circulatory support. Methods: Consecutive patients who received Impella (2.5, CP, and 5.0) support at our institute between March 2018 and July 2021 were retrospectively included. The relationships between the pulmonary artery pulsatility index (PAPi) immediately after Impella insertion and the occurrence of hemolysis were investigated. Results: Forty-two patients (median 71 years old, 60% men) were included. Hemolysis occurred in 20 patients (48%). A cutoff of PAPi to predict hemolysis was calculated as 1.3, with 80.0% sensitivity and 72.7% specificity. Lower PAPi (<1.3) significantly correlated with the occurrence of hemolysis with an odds ratio of 11.65 (95% confidence interval 1.58−85.98, p = 0.017), adjusted for other potential confounders. Survival discharge was significantly lower in patients with lower PAPi (<1.3) (50% vs. 86%, p = 0.019). Conclusions: The results of this study suggest that patients with right ventricular impairment indicated by lower PAPi following the initiation of Impella-incorporated mechanical circulatory support have a higher risk of hemolysis.

Echocardiographic imaging of temporary percutaneous mechanical circulatory support devices

Cardiogenic shock is a state of end-organ hypoperfusion due to primary cardiac dysfunction and portends a poor prognosis. Shock refractory to inotropic and vasopressor support is often an indication for mechanical circulatory support. When mechanical support device complications or malfunction arise, echocardiography offers rapid assessment of device position and function. Repositioning can be done under echocardiographic guidance. Despite the widespread use of percutaneous mechanical circulatory support, there is a dearth of information regarding echocardiography as it pertains to these devices. In this review, we discuss the utility of echocardiography with percutaneous mechanical circulatory support devices.

A Review of the Impella Devices

The use of mechanical circulatory support (MCS) to provide acute haemodynamic support for cardiogenic shock or to support high-risk percutaneous coronary intervention (HRPCI) has grown over the past decade. There is currently no consensus on best practice regarding its use in these two distinct indications. Impella heart pumps (Abiomed) are intravascular microaxial blood pumps that provide temporary MCS during HRPCI or in the treatment of cardiogenic shock. The authors outline technical specifications of the individual Impella heart pumps and their accompanying technology, the Automated Impella Controller and SmartAssist, their indications for use and patient selection, implantation techniques, device weaning and escalation, closure strategies, anticoagulation regimens, complications, future directions and upcoming trials.

Computational Fluid-Structure Interaction Study of a New Wave Membrane Blood Pump

PURPOSE

Wave membrane blood pumps (WMBP) are novel pump designs in which blood is propelled by means of wave propagation by an undulating membrane. In this paper, we computationally studied the performance of a new WMBP design (J-shaped) for different working conditions, in view of potential applications in human patients.

METHODS

Fluid-structure interaction (FSI) simulations were conducted in 3D pump geometries and numerically discretized by means of the extended finite element method (XFEM). A contact model was introduced to capture membrane-wall collisions in the pump head. Mean flow rate and membrane envelope were determined to evaluate hydraulic performance. A preliminary hemocompatibility analysis was performed via calculation of fluid shear stress.

RESULTS

Numerical results, validated against in vitro experimental data, showed that the hydraulic output increases when either the frequency or the amplitude of membrane oscillations were higher, with limited increase in the fluid stresses, suggesting good hemocompatibility properties. Also, we showed better performance in terms of hydraulic power with respect to a previous design of the pump. We finally studied an operating point which achieves physiologic flow rate target at diastolic head pressure of 80 mmHg.

CONCLUSION

A new design of WMBP was computationally studied. The proposed FSI model with contact was employed to predict the new pump hydraulic performance and it could help to properly select an operating point for the upcoming first-in-human trials.

The influence of surface roughness on the damage of von Willebrand Factor under shear flow condition

Despite technological advances in mechanical circulatory support devices to treat end-stage heart failure, blood damage induced by non-physiological shear stress in operation often triggered clinical hemocompatibility complications. The loss of high molecular weight von Willebrand Factor (HMW-VWF) has been considered as an essential cause of gastrointestinal bleeding. In addition to the mechanics factors, interface factors may also affect blood damage, especially the surface characteristics. In this study, the effect of surface roughness on VWF damage under flow condition was investigated. A roller pump circulation experimental platform with a roughness embedded sample chamber was constructed to provide blood shearing flow condition. VWF molecular weight analysis, VWF antigen (VWF-Ag) concentration assay, and VWF ristocetin cofactor activity (VWF-Rico) assay were performed on the sheared blood samples. These variables are the main functional indicators of VWF. It was found that the surface roughness induced VWF damage is mainly caused by the loss of HMW-VWF rather than reducing the total amount of VWF. The threshold value of surface roughness for a rapid increase in the degradation of HMW-VWF under low flow rate was obtained between Ra 0.4 and 0.6 μm, which was smaller than the threshold for hemolysis. Our findings indicated that VWF is more sensitive to the interface factor of surface roughness than red blood cells, thus has a higher requirement for blood pump design. It could provide reference for the material design and processing in developing mechanical circulatory support devices.

Effects of a Short-Term Left Ventricular Assist Device on Hemodynamics in a Heart Failure Patient-Specific Aorta Model: A CFD Study

Patients with heart failure (HF) or undergoing cardiogenic shock and percutaneous coronary intervention require short-term cardiac support. Short-term cardiac support using a left ventricular assist device (LVAD) alters the pressure and flows of the vasculature by enhancing perfusion and improving the hemodynamic performance for the HF patients. However, due to the position of the inflow and outflow of the LVAD, the local hemodynamics within the aorta is altered with the LVAD support. Specifically, blood velocity, wall shear stress, and pressure difference are altered within the aorta. In this study, computational fluid dynamics (CFD) was used to elucidate the effects of a short-term LVAD for hemodynamic performance in a patient-specific aorta model. The three-dimensional (3D) geometric models of a patient-specific aorta and a short-term LVAD, Impella CP, were created. Velocity, wall shear stress, and pressure difference in the patient-specific aorta model with the Impella CP assistance were calculated and compared with the baseline values of the aorta without Impella CP support. Impella CP support augmented cardiac output, blood velocity, wall shear stress, and pressure difference in the aorta. The proposed CFD study could analyze the quantitative changes in the important hemodynamic parameters while considering the effects of Impella CP, and provide a scientific basis for further predicting and assessing the effects of these hemodynamic signals on the aorta.

Heuristic optimization of impeller sidewall gaps-based on the bees algorithm for a centrifugal blood pump by CFD

Optimization studies on blood pumps that require complex designs are gradually increasing in number. The essential design criteria of centrifugal blood pump are minimum shear stress with maximal efficiency. The geometry design of impeller sidewall gaps (blade tip clearance, axial gap, radial gap) is highly effective with regard to these two criteria. Therefore, unlike methods such as trial and error, the optimal dimensions of these gaps should be adjusted via a heuristic method, giving more effective results. In this study, the optimal gaps that can ensure these two design criteria with The Bees Algorithm (BA), which is a population-based heuristic method, are investigated. Firstly, a Computational Fluid Dynamics (CFD) analysis of sample pump models, which are selected according to the orthogonal array and pre-designed with different gaps, are performed. The dimensions of the gaps are optimized through this mathematical model. The simulation results for the improved pump model are nearly identical to those predicted by the BA. The improved pump model, as designed with the optimal gap dimensions so obtained, is able to meet the design criteria better than all existing sample pumps. Thanks to the optimal gap dimensions, it has been observed that compared to average values, it has provided a 42% reduction in aWSS and a 20% increase in efficiency. Moreover, original an approach to the design of impeller sidewall gaps was developed. The results show that computational costs have been significantly reduced by using the BA in blood pump geometry design.