Superior performance of continuous over pulsatile flow ventricular assist devices in the single ventricle circulation: A computational study

This study compares the physiological responses of systemic-to-pulmonary shunted single ventricle patients to pulsatile and continuous flow ventricular assist devices (VADs). Performance differences between pulsatile and continuous flow VADs have been clinically observed, but the underlying mechanism remains poorly understood. Six systemic-to-pulmonary shunted single ventricle patients (mean BSA=0.30 m2) were computationally simulated using a lumped-parameter network tuned to match patient specific clinical data. A first set of simulations compared current clinical implementation of VADs in single ventricle patients. A second set modified pulsatile flow VAD settings with the goal to optimize cardiac output (CO). For all patients, the best-case continuous flow VAD CO was at least 0.99 L/min greater than the optimized pulsatile flow VAD CO (p=0.001). The 25 and 50 mL pulsatile flow VADs exhibited incomplete filling at higher heart rates that reduced CO as much as 9.7% and 37.3% below expectations respectively. Optimization of pulsatile flow VAD settings did not achieve statistically significant (p\u3c0.05) improvement to CO. Results corroborate clinical experience that continuous flow VADs produce higher CO and superior ventricular unloading in single ventricle patients. Impaired filling leads to performance degradation of pulsatile flow VADs in the single ventricle circulation

A Multi-Scale CFD Analysis of Patient-Specific Geometries to Tailor LVAD Cannula Implantation Under Pulsatile Flow Conditions: an investigation aimed at reducing stroke incidence in LVADs

A Left Ventricular Assist Device (LVAD) is a mechanical pump that provides temporary circulatory support when used as bridge-to-transplantation and relieves workload demand placed on a failing heart allowing for myocardia recovery when used as destination therapy. Stroke is the most devastating complication after ventricular assist device (VAD) implantation, with an incidence of 14-47% over 3-6 months. This complication due to thrombus formation and subsequent transport through the vasculature to cerebral vessels continues to limit the widespread implementation of VAD therapy. Patient-specific computational fluid dynamics (CFD) analysis may elucidate ways to reduce this risk. We employed a multi-scale model of the aortic circulation in order to examine the effects on flow conditions resulting from varying the VAD cannula implantation location and angle of incidence of the anastomosis to the ascending aorta based on a patient-specific geometry obtained from CT scans. The multi-scale computation consists of a 0D lumped parameter model (LPM) of the circulation modeled via a 50 degree of freedom (DOF) electrical circuit analogy that includes an LVAD model coupled to a 3D computational fluid dynamics model of the circulation. An in-house adaptive Runge-Kutta method is utilized to solve the 50 DOF LPM, and the Starccm+ CFD code is utilized to solve the flowfield. This 0D-3D coupling for the flow is accomplished iteratively with the 0D LPM providing the pulsatile boundary conditions that drive the 3D CFD time-accurate computations of the flowfield. Investigated angle configurations include cannula implantations at 30°, 60° and 90° to the right lateral wall of the ascending aorta. We also considered placements of the VAD cannula along the ascending aorta in which distances of the VAD anastomosis is varied relative to the take-off of the innominate artery. We implemented a mixed Eulerian-Lagrangian particle-tracking scheme to quantify the number of stroke-inducing particles reaching cerebral vessel outlets and included flow visualization through streamlines to identify regions of strong vorticity and flow stagnation, which can promote thrombus formation. Thrombi were modeled as spheres with perfectly elastic interactions numerically released randomly in time and space at cannula inlet plane. Based on clinical observation of the range of thrombus sizes encountered in such cases, particle diameters of 2.5mm and 3.5mm were investigated in our numerical computations. Pulsatile flow results for aforementioned angles suggest that a 90° cannula implementation causes flow impingement on the left lateral aortic wall and appears to be highly thrombogenic due to large momentum losses and zones of large re-circulation and that shallow and intermediate cannula angles promote more regular flow carrying particles towards the lower body potentially reducing stroke risk. Indications from this pulsatile numerical study suggest that up to a 50% reduction in stroke rate can be achieve with tailoring of cannula implantation. Results are consistent with significant reduction in stroke incidence achieved by tailoring cannula implantation as reported in previous steady flow computations carried out by our group. As such, results of this study suggest that a simple surgical maneuver in the process of VAD implantation may significantly improve patient life

Design and optimisation of an Intra-Aortic Shrouded rotor axial pump

Undesirable side effects in patients with a LVAD (Left Ventricular Assist Device) pump fitted include blood damage, thrombosis, blood traumatisation, and End-Organ Disfunctions. These side effects have generally been attributed to the high wall shear stresses and the induced turbulent flow. In this study, we introduce a novel design to address these effects by lowering the rotational speed and providing an optimum flow path design to minimise blood damage. We present an initial scheme for a new Intra-Aortic Shrouded Rotary Axial Pump and develop a sequence of pump geometries, for which the Taguchi Design Optimisation Method has been applied. We apply CFD tools to simulate the pressure rise, pump performance, hydraulic efficiency, wall shear stress, exposure time and mass flow rate. A prototype pump has been tested in a mock cardiovascular circuit using a water-glycerol solution. The optimum design delivered the desired pressure/mass flow rate characteristics at a significantly low rpm (2900 rpm). As a result, the estimated blood damage index is low, matching the design requirements. The theoretical performance was matched by experimental results. [Abstract copyright: Crown Copyright © 2023. Published by Elsevier Ltd. All rights reserved.

VAD in failing Fontan: simulation of ventricular, cavo-pulmonary and biventricular assistance in systolic/diastolic ventricular dysfunction and in pulmonary vascular resistance increase.

Aim: Due to the lack of donors, VADs could be an alternative to heart transplantation for Failing Fontan patients (PTs). Considering the complex physiopathology and the type of VAD connection, a numerical model (NM) could be useful to support clinical decisions. The aim of this work is to test a NM simulating the VADs effects on failing Fontan for systolic dysfunction (SD), diastolic dysfunction (DD) and pulmonary vascular resistance increase (PRI). Methods: Data of 10 Fontan PTs were used to simulate the PTs baseline using a dedicated NM. Then, for each PTs a SD, a DD and a PRI were simulated. Finally, for each PT and for each pathology, the VADs implantation was simulated. Results: NM can well reproduce PTs baseline. In the case of SD, LVAD increases the cardiac output (CO) (35%) and the arterial systemic pressure (ASP) (25%). With cavo-pulmonary assistance (RVAD) a decrease of inferior vena cava pressure (IVCP) (39%) was observed with 34% increase of CO. With the BIVAD an increase of ASP (29%) and CO (37%) was observed. In the case of DD, the LVAD increases CO (42%), the RVAD decreases the IVCP. In the case of PRI, the highest CO (50%) and ASP (28%) increase is obtained with an RVAD together with the highest decrease of IVCP (53%). Conclusions: The use of NM could be helpful in this innovative field to evaluate the VADs implantation effects on specific PT to support PT and VAD selection

Cavopulmonary Support for Failing Fontan Patients: Computational and In Vitro Assessment

Congenital heart defects are responsible for the mortality of approximately 300,000 newborn each year. One study in 2010 estimated that over 2 million patients were living with congenital heart defects in the United States. Congenital heart defects have the highest hospitalization cost among other birth defect categories. The damage on the U.S economy in 2013 was estimated $6.1 billion. The most complex and severe form of these defects results in single ventricle physiology. Fortunately, over the last 50 years, these patients have been able to survive into adulthood as a result of three stages of surgeries culminating with Fontan operation. However, Fontan operation as the current ultimate palliation of single ventricle defects results in significant late complications. Fontan patients will eventually develop circulatory failure and are in desperate need of an immediate therapeutic solution. A rightsided device surgically placed in the cavopulmonary pathway could technically substitute the missing sub-pulmonary ventricle by generating a mild pressure boost. However, currently, there is no device specifically designed for this application due to the small market size. On the other hand, off-label use of an arterial pump (originally designed for left side application) for the cavopulmonary support remains challenging. This is because the hemodynamic impact of a ventricular assist device (VAD) implanted on the right circulation of a Fontan patient is not yet clear. Moreover, further research is needed to identify the physiological consequences of two clinically-considered surgical configurations (IVC and full assisted configurations) for the cavopulmonary VAD installation, with full and IVC support corresponding to the entire venous return or only the inferior venous return, respectively, being routed through the VAD. First objective of this thesis is surgical planning to accurately predict the outcome of cavopulmonary support in failing Fontan patients and findings of this study will help the surgeons in developing coherent clinical strategies for the cavopulmonary support implementation and tuning. Specific objective 2 will investigate the desired operating region for designing a cavopulmonary blood pump that can offer a promising alternative treatment option for a wide range of failing Fontan patients

From Benchtop to Beside: Patient-specific Outcomes Explained by Invitro Experiment

Study: Recent analyses show that females have higher early postoperative (PO) mortality and right ventricular failure (RVF) than males after left ventricular assist device (LVAD) implantation; and that this association is partially mediated by smaller LV size in females. Benchtop experiments allow us to investigate patient-specific (PS) characteristics in a reproducible way given the fact that the PS anatomy and physiology is mimicked accurately. With multiple heart models of varying LV size, we can directly study the individual effects of titrating the LVAD speed and the resulting bi-ventricular volumes, shedding light on the interplay between LV and RV as well as resulting inter-ventricular septum (IVS) positions, which may cause the different outcomes pertaining to sex. Methods: In vitro, we studied the impact of the heart size to IVS position using two smaller and two larger sized PS silicone heart phantoms derived from clinical CT images (Fig. 1A). With ultrasound crystals that were integrated on a placeholder inflow cannula, the IVS position was measured during LV and RV volume changes (dV) mimicking varying ventricular loading states (Fig. 1B). Figure 1 A Two small (blue) and two large PS heart phantoms (orange) on B benchtop. C Median septum curvature results. LVEDD/LVV/RVV: LV enddiastolic diameter/LV and RV volume. Results: Going from small to large dV, at zero curvature, the septum starts to shift towards the left; for smaller hearts at dV = -40 mL and for larger hearts at dV = -50 mL (Fig. 1C). This result indicates that smaller hearts are more prone to an IVS shift to the left than larger hearts. We conclude that smaller LV size may therefore mediate increased early PO LVAD mortality and RVF observed in females compared to males. Novel 3D silicone printing technology enables us to study accurate, PS heart models across a heterogeneous patient population. PS relationships can be studied simultaneously to clinical assessments and support the decision-making prior to LVAD implantation

Alternative heart assistance pump

2021 Spring.Includes bibliographical references.On average, the human heart beats around 115,000, and pumps around 2,000 gallons of blood daily. This essential organ may undergo systolic or diastolic dysfunction in which the heart cannot properly contract or relax, respectively. To help hearts pump effectively should these types of failures occur, ventricular assist devices (VAD) are implemented as a temporary or permanent solution. The most common VAD is the left ventricular assist device (LVAD) which supports the left ventricle in pumping the oxygen-rich blood from the heart to the aorta, and ultimately to the rest of the body. Although current VADs are an important treatment for advanced heart failure, generally VADS come with many complications and issues after implantation. These complications include incidents of hemolysis (tearing of the blood cells), thrombosis (clotting of the blood), bleeding (especially in the gastrointestinal tract), and infection at the driveline site. Specifically, the current continuous flow pumps are associated with a much higher incidence of gastrointestinal bleeding, myocardial perfusion, kidney problems, among others, compared with the earlier generation pulsatile pumps. However, the presence of several moving mechanical components made the pulsatile pumps less durable, bulky, and prone to malfunction, ultimately leading to favor toward continuous flow designs. The goal of the present study is to develop a novel heart assist pump, overcoming drawbacks to current commercially available pumps, by improving hemodynamic (blood flow) performance, pulsatility, and eliminating bleeding disorders. Our design will overcome the current pumps which suffer from non-physiological flow, and blood damage. The impact of this work goes beyond heart assist devices and would be applicable to other blood pumps. The fundamental biological and physical principles of designing a blood pump will be reviewed in chapter one. In addition, recent studies on current LVADs and the motivation behind these studies will also be discussed. Then, the idea of using a contractive tubular heart as an alternative pump will be presented in chapter two. To understand the pumping mechanism of the tubular heart, a detailed study on the embryonic heart is presented in this chapter. Subsequently, the effect of flow forces on blood cells will be studied in chapter 3. Moreover, the relation between flow regime and bleeding disorders have been studied in the same chapter. A discussion of our design, including the pump design, testing set up, experimental results will be presented in chapter 4. Finally, the limitations of the present study and future work will be presented in chapter 5

Computational and In Vitro Models to Analyze the Interactions of Ventricular Assist Devices and Thromboemboli

Heart failure is consistently one of the top causes of death each year worldwide. Ventricular assist devices (VADs) have become common alternatives for patients with severe, end-stage heart failure; VADs take a significant load off of the heart and aid in perfusion of downstream organs by pumping blood from either or both ventricles to their corresponding great vessel. External VAD controllers track specific pump parameters such as estimated flow rates and device power consumption. Suspected thrombosis is a common clinical adverse event in VAD therapy. In this condition, a VAD controller will indicate periods of low flow or high power; clinicians suspect that this indicates that a thrombus is increasing friction between the moving components and/or obstructing the inflow or outflow. Suspected thrombosis typically results in device exchange surgery. A pathology evaluation of the explanted VAD can reveal if materials inside the pump at explant originated within or upstream from the device. VADs explanted after years of support often had an actively organizing thrombus along the inflow cannula or protruding from the insertion site in the ventricle. We hypothesize that these thrombi form over time due to regions of stagnation and recirculation of the blood in the ventricle. Moreover, as the VAD continues to take a load off of the heart, we suspect that the remodeling of the heart will change the flow dynamics within the ventricle and cause thrombi to dislodge and travel into the pump. As thrombi of different age and size pass into the device, we hypothesize that each VAD model will demonstrate a particular change in flow rate in response to the thrombus. Through the research in this dissertation, we have investigated these phenomena by creating a computational model of the ventricular insertion site before and after cardiac remodeling occurs, and an in vitro model that displays VAD response to thromboembolic particles. These computational and in vitro models show that over time, the presence of the VAD inflow cannula within the heart will change the potential for thrombi to form around the device, dislodge, and travel into the VAD, and result in changes of pump flow rate. This research is beneficial to VAD manufacturers and clinicians in the development of devices that will limit opportunity for thromboembolic complications, and provide direction for treatment of patients currently undergoing VAD therapy