Continuous-Flow Rotary Left Ventricular Assist Devices with “3rd Generation” Design

Pulsatility and flow patterns across macro- and microcirculatory arteries of continuous-flow left ventricular assist device patients

BACKGROUND

Reduced arterial pulsatility in continuous-flow left ventricular assist devices (CF-LVAD) patients has been implicated in clinical complications. Consequently, recent improvements in clinical outcomes have been attributed to the "artificial pulse" technology inherent to the HeartMate3 (HM3) LVAD. However, the effect of the "artificial pulse" on arterial flow, transmission of pulsatility into the microcirculation and its association with LVAD pump parameters is not known.

METHODS

The local flow oscillation (pulsatility index, PI) of common carotid arteries (CCAs), middle cerebral arteries (MCAs) and central retinal arteries (CRAs-representing the microcirculation) were quantified by 2D-aligned, angle-corrected Doppler ultrasound in 148 participants: healthy controls, n = 32; heart failure (HF), n = 43; HeartMate II (HMII), n = 32; HM3, n = 41.

RESULTS

In HM3 patients, 2D-Doppler PI in beats with "artificial pulse" and beats with "continuous-flow" was similar to that of HMII patients across the macro- and microcirculation. Additionally, peak systolic velocity did not differ between HM3 and HMII patients. Transmission of PI into the microcirculation was higher in both HM3 (during the beats with "artificial pulse") and in HMII patients compared with HF patients. LVAD pump speed was inversely associated with microvascular PI in HMII and HM3 (HMII, r2 = 0.51, p < 0.0001; HM3 "continuous-flow," r2 = 0.32, p = 0.0009; HM3 "artificial pulse," r2 = 0.23, p = 0.007), while LVAD pump PI was only associated with microcirculatory PI in HMII patients.

CONCLUSIONS

The "artificial pulse" of the HM3 is detectable in the macro- and microcirculation but without creating a significant alteration in PI compared with HMII patients. Increased transmission of pulsatility and the association between pump speed and PI in the microcirculation indicate that the future clinical care of HM3 patients may involve individualized pump settings according to the microcirculatory PI in specific end-organs.

Computational Evaluation of Cardiac Function in Children Supported with Heartware VAD, HeartMate 2 and HeartMate 3 Left Ventricular Assist Devices

Heart failure is one of the principal causes of morbidity and mortality in children. Treatment techniques may not work, and heart transplantation may be required as a result. The current state of donor-organ supply means that many patients cannot undergo transplantation. In these patients, ventricular assist devices (VADs) may be used to bridge the time until the transplantation. Continuous-flow VADs are increasingly being implanted to paediatric patients. The aim of this study was to evaluate cardiac function in children supported with Heartware HVAD, HeartMate2 and HeartMate3 devices using computational simulations. A lumped-parameter model simulating cardiac function in children around 12 years of age was used to simulate dilated cardiomyopathy and heart-pump support. The operating speeds in HVAD, HeartMate2 and HeartMate3 were selected as 2600 rpm, 8700 rpm and 5200 rpm constant speed, respectively, while the Lavare cycle and artificial-pulse modes were used to generate mean pump outputs at around 4.40 L/min and mean arterial pressures at around 82 mmHg in each device. Aortic pulse pressure was 11 mmHg, 14 mmHg and 6 mmHg under HVAD, HeartMate2 and HeartMate3 support, respectively. HVAD’s Lavare cycle and HeartMate3’s artificial pulse increased aortic pulse pressure to 15 mmHg and 20 mmHg. HeartMate3 with artificial-pulse mode may be more beneficial in reducing arterial-pulsatility-associated problems.

Effects of Acute Pump Speed Changes on Cerebral Hemodynamics in Patients With an Implantable Continuous-Flow Left Ventricular Assist Devices

Mechanical circulatory support (MCS) with an implantable left ventricular assist device (LVAD) is an established therapeutic option for advanced heart failure. Most of the currently used LVADs generate a continuous stream of blood that decreases arterial pulse pressure. This study investigated whether a change of the pulse pressure during different pump speed settings would affect cerebral autoregulation and thereby affect cerebral blood flow (CBF). The study included 21 haemodynamically stable outpatients with a continuous-flow LVAD (HeartMate II, Abbott, USA) implanted a median of 6 months before the study (interquartile range 3 to 14 months). Arterial blood pressure (measured by finger plethysmography) was recorded simultaneously with CBF (measured by transcranial Doppler ultrasound) during baseline pump speed (8900 rpm [IQR 8800; 9200]) and during minimum and maximum tolerated pump speeds (8000 rpm [IQR 8000; 8200] and 9800 rpm [IQR 9800; 10 000]). An increase in LVAD pump speed by 800 rpm [IQR 800; 1000] from the baseline lead to a significant decrease in arterial pulse pressure and cerebral blood flow pulsatility (relative change -24% and -32%, both p < 0.01), but it did not affect mean arterial pressure and mean CBF velocity (relative change 1% and -1.7%, p = 0.1 and 0.7). In stable patients with a continuous-flow LVAD, changes of pump speed settings within a clinically used range did not impair static cerebral autoregulation and cerebral blood flow.

Ablation therapy for ventricular arrhythmias in patients with LVAD: Multiple faces of an electrophysiological challenge

Left ventricular assist device implantation is a recognized treatment option for patients with advanced heart failure refractory to medical therapy and can be used both as bridge to transplantation and as destination therapy. The risk of ventricular arrhythmias is common after left ventricular assist device implantation and is influenced by pre-, peri and post-operative determinants. The management of ventricular arrhythmias can be a challenge when they become refractory to medication or to device therapy and their impact on prognosis can be detrimental despite the mechanical support. In this setting, catheter ablation is being increasingly recognized as a feasible option for patients in which standard therapeutic strategies fail, but also with preventive purpose. Catheter ablation is being increasingly considered for the management of ventricular arrhythmias in patients with left ventricular assist device despite complex clinical and technical peculiarities due to the characteristics of the mechanical support. Much conflicting data exist regarding the predictors of success of the procedure and the rate of recurrence. In this review we discuss the latest evidences regarding catheter ablation of ventricular arrhythmias in this subset of patients, focusing on clinical characteristics, arrhythmia etiology, technical aspects and postprocedural features which must be considered by the electrophysiologist.

Correlation between Myocardial Function and Electric Current Pulsatility of the Sputnik Left Ventricular Assist Device: In-Vitro Study

This study assesses the electric current parameters and reports on the analysis of the associated degree of myocardial function during left ventricular assist device (LVAD) support. An assumption is made that there is a correlation between cardiac output and the pulsatility index of the pump electric current. The experimental study is carried out using the ViVitro Pulse Duplicator System with Sputnik LVAD connected. Cardiac output and cardiac power output are used as a measure of myocardial function. Different heart rates (59, 73, 86 bpm) and pump speeds (7600–8400 rpm in 200 rpm steps) are investigated. In our methodology, ventricular stroke volumes in the range of 30–80 mL for each heart rate at a certain pump speed were used to simulate different levels of contractility. The correlation of the two measures of myocardial function and proposed pulsatility index was confirmed using different correlation coefficients (values ≥ 0.91). Linear and quadratic models for cardiac output and cardiac power output versus pulsatility index were obtained using regression analysis of measured data. Coefficients of determination for CO and CPO models were in the ranges of 0.914–0.982 and 0.817–0.993, respectively. Study findings suggest that appropriate interpretation of parameters could potentially serve as a valuable clinical tool to assess myocardial therapy using LVAD infrastructure.

Comparative assessment of different versions of axial and centrifugal LVADs: A review

Continuous-flow left ventricular assist devices (LVADs) have gained tremendous acceptance for the treatment of end-stage heart failure patients. Among different versions, axial flow and centrifugal flow LVADs have shown remarkable potential for clinical implants. It is also very crucial to know which device serves its purpose better to treat heart failure patients. A thorough comparison of axial and centrifugal LVADs, which may guide doctors in deciding before the implant, still lacks in the literature. In this work, an assessment of axial and centrifugal LVADs has been made to suggest a better device by comparing their engineering, clinical, and technological development of design aspects. Hydrodynamic and hemodynamic aspects for both types of pumps are discussed along with their biocompatibility, bearing types, and sizes. It has been observed numerically that centrifugal LVADs perform better over axial LVADs in every engineering aspect like higher hydraulic efficiency, better characteristics curve, lesser power intake, and also lesser blood damage. However, the clinical outcomes suggest that centrifugal LVADs experience higher events of infections, renal, and respiratory dysfunction. In contrast, axial LVADs encountered higher bleeding and cardiac arrhythmia. Moreover, recent technological developments suggested that magnetic type bearings along with biocompatible coating improve the life of LVADs.

Impairments in Blood Pressure Regulation and Cardiac Baroreceptor Sensitivity Among Patients With Heart Failure Supported With Continuous-Flow Left Ventricular Assist Devices

BACKGROUND

Continuous-flow (CF) left ventricular assist devices (LVADs) improve outcomes for patients with advanced heart failure (HF). However, the lack of a physiological pulse predisposes to side-effects including uncontrolled blood pressure (BP), and there are little data regarding the impact of CF-LVADs on BP regulation.

METHODS

Twelve patients (10 males, 60±11 years) with advanced heart failure completed hemodynamic assessment 2.7±4.1 months before, and 4.3±1.3 months following CF-LVAD implantation. Heart rate and systolic BP via arterial catheterization were monitored during Valsalva maneuver, spontaneous breathing, and a 0.05 Hz repetitive squat-stand maneuver to characterize cardiac baroreceptor sensitivity. Plasma norepinephrine levels were assessed during head-up tilt at supine, 30^o and 60^o. Heart rate and BP were monitored during cardiopulmonary exercise testing.

RESULTS

Cardiac baroreceptor sensitivity, determined by Valsalva as well as Fourier transformation and transfer function gain of Heart rate and systolic BP during spontaneous breathing and squat-stand maneuver, was impaired before and following LVAD implantation. Norepinephrine levels were markedly elevated pre-LVAD and improved-but remained elevated post-LVAD (supine norepinephrine pre-LVAD versus post-LVAD: 654±437 versus 323±164 pg/mL). BP increased during cardiopulmonary exercise testing post-LVAD, but the magnitude of change was modest and comparable to the changes observed during the pre-LVAD cardiopulmonary exercise testing.

CONCLUSIONS

Among patients with advanced heart failure with reduced ejection fraction, CF-LVAD implantation is associated with modest improvements in autonomic tone, but persistent reductions in cardiac baroreceptor sensitivity. Exercise-induced increases in BP are blunted. These findings shed new light on mechanisms for adverse events such as stroke, and persistent reductions in functional capacity, among patients supported by CF-LVADs. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03078972.

Improvement of hemolysis performance in a hydrodynamically levitated centrifugal blood pump by optimizing a shroud size

We have developed a hydrodynamically levitated centrifugal blood pump. In the blood pump having hydrodynamic bearings, the narrow bearing gap has a potential for high hemolysis. The purpose of the this study is to improve hemolysis performance in a hydrodynamically levitated centrifugal blood pump by optimizing a shroud size. The impeller was levitated passively at the position where the thrust forces acting on the impeller were balanced. We focused on a size of a bottom shroud with a hydrodynamic bearing that could change the bottom hydrodynamic force to balance the thrust force at the wide bearing gap for reducing hemolysis. Five test models with various shroud size were compared: 989 mm² (HH-10.5), 962 mm² (HH-12), 932 mm² (HH-13.5), 874 mm² (HH-16), and 821 mm² (HH-18). A numerical analysis was first performed to estimate the bearing gaps in the test model. The bearing gaps were then measured to validate the numerical analysis. Finally, an in vitro hemolysis test was performed. The numerical analysis revealed that the HH-13.5 model had the widest bearing gap of 129 µm. In the measurement test, the estimation error for the bearing gap was less than 10%. In the hemolysis test, the HH-13.5 model achieved the lowest hemolysis level among the five models. The present study demonstrated that the numerical analysis was found to be effective for determining the optimal should size, and the HH-13.5 model had the optimal shroud size in the developed hydrodynamically levitated centrifugal blood pump to reduce hemolysis.

Correction of High Afterload Improves Low Cardiac Output in Patients Supported on Left Ventricular Assist Device Therapy

There is a paucity of data describing the invasive assessment of afterload and influence on cardiac output in patients supported on left ventricular assist device (LVAD) therapy. From 2015 to 2018, patients on LVAD therapy were evaluated with simultaneous left/right heart catheterization ramp study for speed optimization. Hemodynamic parameters from 31 patients without significant aortic insufficiency were analyzed. Mean central aortic pressure (MAP) was elevated at 87 ± 13 mm Hg at baseline. No direct association between MAP and cardiac index (CI) was found (r = 0.11, p = 0.20). However, variable MAP provided vastly different patterns of cardiac output response to speed increments (positive correlation, p = 0.047 for MAP <80 mm Hg; negative trend, p = 0.25 for MAP > 100 mm Hg). Patients noted to be hypertensive (MAP > 90, n = 8) received nitrate therapy and experienced both improvement in biventricular filling pressures and a mean increase in CI from 2.4 to 2.9 L/min/m2 (+22%, p = 0.04) at a fixed revolutions per minute. High afterload is common in patients on LVAD therapy, is associated with poor response to ramp, and is ameliorated by nitrates. These findings serve as a foundation to evaluate the dynamic effects of high afterload and chronic vasodilator therapy in patients with durable LVADs.

Numerical and Experimental Approach to Characterize a BLDC Motor with Different Radial-gap to Improve Hemocompatibility Performance

Left ventricular assist devices (LVADs) have increasingly been used clinically to treat heart failure patients. However, hemolysis, pump thrombosis, infection and bleeding still persist as major limitations of LVAD technology. Assessing LVAD hemocompatibility using a blood shear stress device (BSSD) has clear advantages, as the BSSD could provide a better experimental platform to develop reliable, quantifiable blood trauma assays to perform iterative testing of LVAD designs. In this study, a BSSD was proposed with short blood exposure time and no seals or contact bearings to reduce blood trauma caused by the test platform. Enlarged air-gap drive motor in BSSD is essential to avoid high shear stress; however, it would significantly reduce the motor torque, which may result in inadequate force to drive the entire system. In order to evaluate and optimize the drive motor air-gap to ensure adequate motor torque as well as acceptable range for blood exposure time and shear stress, a numerical brushless DC (BLDC) motor model was established using finite element method (FEM) in numerical simulation software COMSOL. The model was first validated by the experimental results. Then numerical model with different air-gap was evaluated on the torque and speed constant changes. In the end, two equations were generated based on the curves derived from the torque and speed constant calculations. Determining these relationships between motor performance and motor air-gap will facilitate the development of an appropriate BLDC motor size for the BSSD, considering the design limitations in our future work.

Left Ventricular Assist Device as Destination Therapy: a State of the Science and Art of Long-Term Mechanical Circulatory Support

PURPOSE OF REVIEW

The purpose of this review is to synthesize and summarize recent developments in the care of patients with end-stage heart failure being managed with a left ventricular assist device (LVAD) as destination therapy.

RECENT FINDINGS

Although the survival of patients treated with LVAD continues to improve, the rates of LVAD-associated complication, such as right ventricular failure, bleeding complications, and major infection, remain high, and management of these patients remains challenging. The durability and hemocompatibility of LVAD support have greatly increased in recent years as a result of new technologies and novel management strategies. Challenges remain in the comprehensive care of patients with destination therapy LVADs, including management of comorbidities and optimizing patient function and quality of life.

Bionic women and men - Part 1: Cardiovascular lessons from heart failure patients implanted with left ventricular assist devices

NEW FINDINGS

What is the topic of this review? Patients with advanced heart failure who are implanted with left ventricular assist devices (LVADs) present an opportunity to understand the human circulation under extreme conditions. What advances does it highlight? LVAD patients have a unique circulation that is characterized by a reduced or even absent arterial pulse. The remarkable survival of these patients is accompanied by circulatory complications, including stroke, gastrointestinal bleeding and right-heart failure. Understanding the mechanisms related to the complications in LVAD patients will help the patients and also advance our fundamental understanding of the human circulation in general.

ABSTRACT

Some humans with chronic, advanced heart failure are surgically implanted with a left ventricular assist device (LVAD). Because the LVAD produces a continuous flow, a palpable pulse is often absent in these patients. This allows for a unique investigation of the human circulation and has created a controversy around the 'need' for a pulse. The medical debate has also generated a more generic, fundamental discussion into what is 'normal' arterial physiology and health. The comprehensive study and understanding of the arterial responses to drastically altered haemodynamics due to continuous-flow LVADs, at rest and during activity, presents an opportunity to significantly increase our current understanding of the fundamental components of arterial regulation (flow, blood pressure, sympathetic activity, endothelial function, pulsatility) in a way that could never have been studied previously. In a series of four articles, we summarize the talks presented at the symposium entitled 'Bionic women and men - Physiology lessons from implantable cardiac devices' presented at the 2019 Annual Meeting of The Physiological Society in Aberdeen, UK. The articles highlight the novel questions generated by physiological phenomena observed in LVAD patients and propose future areas of interest within the field of cardiovascular physiology.

Device Therapy and Arrhythmia Management in Left Ventricular Assist Device Recipients: A Scientific Statement From the American Heart Association

Left ventricular assist devices (LVADs) are an increasingly used strategy for the management of patients with advanced heart failure with reduced ejection fraction. Although these devices effectively improve survival, atrial and ventricular arrhythmias are common, predispose these patients to additional risk, and complicate patient management. However, there is no consensus on best practices for the medical management of these arrhythmias or on the optimal timing for procedural interventions in patients with refractory arrhythmias. Although the vast majority of these patients have preexisting cardiovascular implantable electronic devices or cardiac resynchronization therapy, given the natural history of heart failure, it is common practice to maintain cardiovascular implantable electronic device detection and therapies after LVAD implantation. Available data, however, are conflicting on the efficacy of and optimal device programming after LVAD implantation. Therefore, the primary objective of this scientific statement is to review the available evidence and to provide guidance on the management of atrial and ventricular arrhythmias in this unique patient population, as well as procedural interventions and cardiovascular implantable electronic device and cardiac resynchronization therapy programming strategies, on the basis of a comprehensive literature review by electrophysiologists, heart failure cardiologists, cardiac surgeons, and cardiovascular nurse specialists with expertise in managing these patients. The structure and design of commercially available LVADs are briefly reviewed, as well as clinical indications for device implantation. The relevant physiological effects of long-term exposure to continuous-flow circulatory support are highlighted, as well as the mechanisms and clinical significance of arrhythmias in the setting of LVAD support.

Left Ventricular Assist Device: What the Internist Needs to Know. A Review of the Literature

Left ventricular assist devices (LVADs) have revolutionized therapy for patients with Stage D heart failure (HF) with reduced systolic function providing not only improved survival benefits but also meaningful changes in quality of life and functional capacity. With technological advances and improved durability of devices, length of survival has significantly improved. With continued organ donor shortage, LVADs are frequently serving as a substitute for cardiac transplant as destination therapy, particularly among the elderly. Internists not only face the important challenge of identifying the patients in need referral for these advanced therapies, they are also faced with the challenges of taking care of these patients. This review will help the internists to better understand the present status, indications and advances in LVADs and also understand the complications and adverse effects associated with these devices.

Measuring real-time blood viscosity with a ventricular assist device

Ventricular assist devices assist in blood circulation and form a crucial component of artificial hearts. While it is important to measure parameters such as the flow rate, pressure head and viscosity of the blood, implanting additional devices to do such measurements is inadvisable. To this end, we demonstrate the adaptation of a ventricular assist device for the purpose of measuring blood viscosity. Such an approach eliminates the need for additional dedicated viscometers in artificial hearts. In the proposed method, the blood viscosity is measured by applying radial vibrational excitation to the impeller in a ventricular assist device using its magnetic levitation system. During the measurement, blood is exposed to a combination of a low shear rate (≈100/s) generated by the radial vibration of the impeller and a high shear rate (>10,000/s) generated by the impeller’s rotation. The apparent viscosity of blood depends on the shear rate, so we determined which shear rate was the dominant one in the proposed method. The measurement results showed that the viscosity measured by the proposed method was in good agreement with the reference viscosity measured with a high shear rate. The mean absolute deviation in the measurements using the proposed method and those obtained using a concentric cylindrical viscometer at a high shear rate was 0.12 mPa s for four samples of porcine blood, with viscosities ranging from 2.32 to 2.75 mPa s.

Design Method Using Statistical Models for Miniature Left Ventricular Assist Device Hydraulics

Left ventricular assist devices (LVADs) are increasingly used to treat heart failure patients. These devices' impeller blades and diffuser vanes must be designed for hydraulic performance and hemocompatibility. The traditional design method, applying mean-line theory, is not applicable to the design of small-scale pumps such as miniature LVADs. Furthermore, iterative experimental testing to determine how each geometric variable affects hydraulic performance is time and labor intensive. In this study, we tested a design method wherein empirical hydraulic results are used to establish a statistical model to predict pump hydraulic performance. This method was used to design an intra-atrial blood pump. Five geometric variables were chosen, and each was assigned two values to define the variable space. The experimental results were then analyzed with both correlation analysis and linear regression modeling. To validate the linear regression models, 2 test pumps were designed: mean value of each geometric variable within the boundaries, and random value of each geometric variable within the boundaries. The statistical model accurately predicted the hydraulic performance of both pump designs within the boundary space. This method could be expanded to include more geometric variables and broader boundary conditions, thus accelerating the design process for miniature LVADs.

Rotary mechanical circulatory support systems

A detailed survey of the current trends and recent advances in rotary mechanical circulatory support systems is presented in this paper. Rather than clinical reports, the focus is on technological aspects of these rehabilitating devices as a reference for engineers and biomedical researchers. Existing trends in flow regimes, flow control, and bearing mechanisms are summarized. System specifications and applications of the most prominent continuous-flow ventricular assistive devices are provided. Based on the flow regime, pumps are categorized as axial flow, centrifugal flow, and mixed flow. Unique characteristics of each system are unveiled through an examination of the structure, bearing mechanism, impeller design, flow rate, and biocompatibility. A discussion on the current limitations is provided to invite more studies and further improvements.

Ventricular Assist Devices: Current State and Challenges

Cardiovascular disease (CVD), as the most prevalent human disease, incorporates a broad spectrum of cardiovascular system malfunctions/disorders. While cardiac transplantation is widely acknowledged as the optional treatment for patients suffering from end-stage heart failure (HF), due to its related drawbacks, such as the unavailability of heart donors, alternative treatments, i.e., implanting a ventricular assist device (VAD), it has been extensively utilized in recent years to recover heart function. However, this solution is thought problematic as it fails to satisfactorily provide lifelong support for patients at the end-stage of HF, nor does is solve the problem of their extensive postsurgery complications. In recent years, the huge technological advancements have enabled the manufacturing of a wide variety of reliable VAD devices, which provides a promising avenue for utilizing VAD implantation as the destination therapy (DT) in the future. Along with typical VAD systems, other innovative mechanical devices for cardiac support, as well as cell therapy and bioartificial cardiac tissue, have resulted in researchers proposing a new HF therapy. This paper aims to concisely review the current state of VAD technology, summarize recent advancements, discuss related complications, and argue for the development of the envisioned alternatives of HF therapy.

Left Ventricular Assist Devices: A Rapidly Evolving Alternative to Transplant

Left ventricular assist devices are becoming an increasingly prevalent therapy for patients with Stage D heart failure with reduced ejection fraction. Technological advances have improved the durability of these devices and have significantly lengthened survival in these patients. Quality of life is also improved, although adverse events related to device therapy remain common. Nevertheless, with the continuing organ donor shortage for cardiac transplantation, left ventricular assist devices are frequently serving as a substitute for transplant, particularly in the elderly patient.

Predictors of 30-day post-transplant mortality in patients bridged to transplantation with continuous-flow left ventricular assist devices--An analysis of the International Society for Heart and Lung Transplantation Transplant Registry

BACKGROUND

Continuous-flow (CF) left ventricular assist devices (LVADs) are standard of care for bridging patients to cardiac transplantation. However, existing data about preoperative factors influencing early post-transplant survival in these patients are limited. We sought to determine risk factors for mortality using a large international database.

METHODS

All patients in the International Society for Heart and Lung Transplantation Transplant Registry who were bridged to transplantation with CF LVADs between June 2008 and June 2012 were included. Risk factors for mortality within 30 days of transplant were identified. Statistical analysis included multivariable analysis and Kaplan-Meier survival analysis.

RESULTS

During the study period, 2,152 patients with CF LVADs underwent heart transplantation. Post-transplant survival was 95.5% at 30 days. Risk factors for mortality during this window included ventilator support at transplant (hazard ratio [HR] = 5.00, 95% confidence interval [CI] = 1.51-16.58), female recipient/male donor (compared with all other combinations, HR = 3.29, 95% CI = 1.90-5.72), history of hemodialysis (HR = 2.51, 95% CI = 1.14-5.51), and history of coronary bypass grafting (HR = 1.89, 95% CI = 1.19-3.00). Increasing recipient age (p = 0.002), body mass index (p = 0.002), creatinine (p = 0.004), and total bilirubin (p < 0.001) also were associated with an increase in mortality.

CONCLUSIONS

In patients supported with CF LVADs, risk factors for early mortality can be identified before transplant, including ventilator support, female recipient/male donor, increasing recipient age, and body mass index. Despite the inherent complexities of a reoperative surgery, patients bridged to transplant with CF LVADs have excellent peri-operative survival.

Evaluation of a Spiral Groove Geometry for Improvement of Hemolysis Level in a Hydrodynamically Levitated Centrifugal Blood Pump

The purpose of this study is to evaluate a spiral groove geometry for a thrust bearing to improve the hemolysis level in a hydrodynamically levitated centrifugal blood pump. We compared three geometric models: (i) the groove width is the same as the ridge width at any given polar coordinate (conventional model); (ii) the groove width contracts inward from 9.7 to 0.5 mm (contraction model); and (iii) the groove width expands inward from 0.5 to 4.2 mm (expansion model). To evaluate the hemolysis level, an impeller levitation performance test and in vitro hemolysis test were conducted using a mock circulation loop. In these tests, the driving conditions were set at a pressure head of 200 mm Hg and a flow rate of 4.0 L/min. As a result of the impeller levitation performance test, the bottom bearing gaps of the contraction and conventional models were 88 and 25 μm, respectively. The impeller of the expansion model touched the bottom housing. In the hemolysis test, the relative normalized index of hemolysis (NIH) ratios of the contraction model in comparison with BPX-80 and HPM-15 were 0.6 and 0.9, respectively. In contrast, the relative NIH ratios of the conventional model in comparison with BPX-80 and HPM-15 were 9.6 and 13.7, respectively. We confirmed that the contraction model achieved a large bearing gap and improved the hemolysis level in a hydrodynamically levitated centrifugal blood pump.

Long-term continuous-flow left ventricular assist devices (LVAD) as bridge to heart transplantation

Heart transplantation (HTx) is the treatment of choice for end-stage heart failure but the limited availability of heart's donors still represents a major issue. So long-term mechanical circulatory support (MCS) has been proposed as an alternative treatment option to assist patients scheduled on HTx waiting list bridging them for a variable time period to cardiac transplantation-the so-called bridge-to-transplantation (BTT) strategy. Nowadays approximately 90% of patients being considered for MCS receive a left ventricular assist device (LVAD). In fact, LVAD experienced several improvements in the last decade and the predominance of continuous-flow over pulsatile-flow technology has been evident since 2008. The aim of the present report is to give an overview of continuous-flow LVAD utilization in the specific setting of the BTT strategy taking into consideration the most representative articles of the scientific literature and focusing the attention on the evolution, clinical outcomes, relevant implications on the HTx strategy and future perspectives of the continuous-flow LVAD technology.

Optimal design of the hydrodynamic multi-arc bearing in a centrifugal blood pump for the improvement of bearing stiffness and hemolysis level

The purpose of the present study is to establish an optimal design of the multi-arc hydrodynamic bearing in a centrifugal blood pump for the improvement of bearing stiffness and hemolysis level. The multi-arc bearing was designed to fulfill the required specifications: (i) ensuring the uniform bearing stiffness for various bearing angles; (ii) ensuring a higher bearing stiffness than the centrifugal force to prevent impeller whirl; and (iii) adjusting the bearing clearance as much as possible to reduce hemolysis. First, a numerical analysis was performed to optimize three design parameters of the multi-arc bearing: number of arcs N, bearing clearance C, and groove depth H. To validate the accuracy of the numerical analysis, the impeller trajectories for six pump models were measured. Finally, an in vitro hemolysis test was conducted to evaluate the hemolytic property of the multi-arc bearing. As a result of the numerical analysis, the optimal parameter combination was determined as follows: N=4, C=100 μm, and H ≥ 100 μm. In the measurements of the impeller trajectory, the optimal parameter combination was found to be as follows: N=4, C=90 μm, and H=100 μm. This result demonstrated the high reliability of the numerical analysis. In the hemolysis test, the parameter combination that achieved the smallest hemolysis was obtained as follows: N=4, C=90 μm, and H=100 μm. In conclusion, the multi-arc bearing could be optimized for the improvement of bearing stiffness and hemolysis level.

Axial and centrifugal continuous-flow rotary pumps: a translation from pump mechanics to clinical practice

The recent success of continuous-flow circulatory support devices has led to the growing acceptance of these devices as a viable therapeutic option for end-stage heart failure patients who are not responsive to current pharmacologic and electrophysiologic therapies. This article defines and clarifies the major classification of these pumps as axial or centrifugal continuous-flow devices by discussing the difference in their inherent mechanics and describing how these features translate clinically to pump selection and patient management issues. Axial vs centrifugal pump and bearing design, theory of operation, hydrodynamic performance, and current vs flow relationships are discussed. A review of axial vs centrifugal physiology, pre-load and after-load sensitivity, flow pulsatility, and issues related to automatic physiologic control and suction prevention algorithms is offered. Reliability and biocompatibility of the two types of pumps are reviewed from the perspectives of mechanical wear, implant life, hemolysis, and pump deposition. Finally, a glimpse into the future of continuous-flow technologies is presented.

Left ventricular assist devices: from the bench to the clinic

The development of ventricular assist devices (VADs) over the past 5 decades as therapy for advanced heart failure (HF) has been extraordinary. Since the original VAD design by Michael DeBakey in the early 1960s, numerous devices for mechanical circulatory support have been engineered, assessed in preclinical studies, applied to human patients in large multicenter clinical trials, and now, select devices are Food and Drug Administration-approved therapy for advanced HF patients. This review highlights select examples of durable VADs from the engineering aspect of design and conception to experimental studies and clinical application underscoring the remarkable progression of such technology to now becoming the standard of care for many advanced HF patients.

Can a Central Stitch over the Arantius' Nodules Provide a Solution for Pre-Operative Severe Native AI in LVAD Patients?

Purpose

To evaluate the evolution of aortic valve insufficiency (AI) after Park's central stitch in patients with severe, pre-operative, native aortic valve insufficiency.

Methods

We retrospectively studied 71 continuous flow LVAD patients between January 2004 and December 2010. Four patients with AI≥3/4 were treated with a central stitch. An intensive review of the literature was performed to debate the use of the central stitch in this population.

Results

The AI at baseline (AI = 2.75 ± 0.5) and AI at last measurement (AI = 0.75 ± 0.65) is statistically different after central stitch (p<0.05) with mean follow up of 198.25 (± 146.70) days. Total cross clamp-time during the placement of the stitch was 15.5 minutes (± 13.062). CVA was not diagnosed in our cohort.

Conclusions

Park's central stitch can be successfully performed on patients with severe native AI (≥3/4) with good long-term results. Short ischemic time and simple application of the stitch are the biggest advantages. Due to the progression of AI in longstanding LVAD, the central stitch may be beneficial for LVAD in destination therapy. Since this is a small group of patients and also an early experience, more cases will be necessary to confirm these positive results.

Development of aortic insufficiency in patients supported with continuous flow left ventricular assist devices

Development of aortic insufficiency (AI) in patients supported with continuous flow left ventricular assist devices (LVAD) can adversely affect pump performance. In this study, we examined the incidence of new AI after LVAD implant at our institution. Pre- and postoperative echocardiograms of 66 patients who received HeartMate II or Heartware LVAD at our institution since June 2008 were reviewed for presence of new AI. Median LVAD support duration was 221 days. New AI developed in 6 patients (9.5%) after a median time of 374.5 days of support. There were no cases of severe or symptomatic AI. There was no significant difference between the AI incidence between HeartMate II and Heartware recipients. For patients who remained on LVAD support at 6 and 12 months, freedom from AI was 100% and 68.4%, respectively. Age, destination therapy status, and duration of support were predictors of new AI after LVAD implant. In conclusion, AI develops frequently during long-term support with continuous flow LVADs, particularly in those supported for longer than 6 months. As we move to the era of long-term LVAD support and destination therapy, further studies with longer follow-ups are required to determine the progression and clinical significance of AI in these patients.

Third-generation continuous flow left ventricular assist devices

Tremendous advances have been made in the treatment of end-stage heart failure patients with left ventricular assist devices (LVADs). An important factor playing a role in the improved clinical outcomes is the development of continuous flow, rotary LVADs. New technology using magnetic levitation and hydrodynamic suspension to eliminate contact bearings offers the potential of more durable and efficacious mechanical circulatory blood pumps. Clinical trials evaluating these novel "third-generation" LVADs are in progress.

Use of an intrapericardial, continuous-flow, centrifugal pump in patients awaiting heart transplantation

BACKGROUND

Contemporary ventricular assist device therapy results in a high rate of successful heart transplantation but is associated with bleeding, infections, and other complications. Further reductions in pump size, centrifugal design, and intrapericardial positioning may reduce complications and improve outcomes.

METHODS AND RESULTS

We studied a small, intrapericardially positioned, continuous-flow centrifugal pump in patients requiring an implanted ventricular assist device as a bridge to heart transplantation. The course of investigational pump recipients was compared with that of patients implanted contemporaneously with commercially available devices. The primary outcome, success, was defined as survival on the originally implanted device, transplantation, or explantation for ventricular recovery at 180 days and was evaluated for both noninferiority and superiority. Secondary outcomes included a comparison of survival between groups and functional and quality-of-life outcomes and adverse events in the investigational device group. A total of 140 patients received the investigational pump, and 499 patients received a commercially available pump implanted contemporaneously. Success occurred in 90.7% of investigational pump patients and 90.1% of controls, establishing the noninferiority of the investigational pump (P<0.001; 15% noninferiority margin). At 6 months, median 6-minute walk distance improved by 128.5 m, and both disease-specific and global quality-of-life scores improved significantly.

CONCLUSIONS

A small, intrapericardially positioned, continuous-flow, centrifugal pump was noninferior to contemporaneously implanted, commercially available ventricular assist devices. Functional capacity and quality of life improved markedly, and the adverse event profile was favorable.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00751972.

Allograft rejection in patients supported with continuous-flow left ventricular assist devices

BACKGROUND

Both pulsatile-flow and continuous-flow left ventricular assist devices (LVADs) successfully provide patients a bridge to transplantation. Some data suggest that continuous-flow pumps increase the risk of allograft rejection, contributing to posttransplantation morbidity and mortality. We sought to analyze the relationship between LVAD flow characteristics and subsequent allograft rejection in bridge to transplant (BTT) patients.

METHODS

Patients with LVADs from the UTAH Transplant Affiliated Hospitals were retrospectively analyzed. Rejection was determined pathologically according to the International Society for Heart and Lung Transplantation revised cardiac allograft rejection scale. Multimodal statistical analyses were applied.

RESULTS

Of 1,076 patients who underwent transplantation over a 26-year period, 151 had LVADs. Of these, 111 (77 pulsatile flow, 34 continuous flow) patients had pathologic data available. There was no difference in overall rejection (grades 1R to 3R) between the pulsatile-flow LVAD and continuous-flow LVAD groups (2.00 ± 1.43 versus 1.50 ± 1.16 episodes/year; p = 0.076.) Patients with pulsatile-flow LVADs had more clinically relevant (grades 2R to 3R) rejection than did patients with continuous-flow LVADs (0.49 ± 0.72 versus 0.12 ± 0.33 episodes/year; p < 0.001). There was no survival difference at 1 year (p = 0.920) or 4 years (p = 0.721) after transplantation.

CONCLUSIONS

Patients with continuous-flow LVADs have similar overall rejection rates and a reduced rate of clinically relevant rejection compared with patients with pulsatile-flow LVADs during the first year after transplantation. Although there is theoretical concern that nonphysiologic, nonpulsatile flow could alter the neurohormonal profile of patients in heart failure, we are encouraged that the type of LVAD circulation does not influence posttransplantation allograft survival.

A review of clinical ventricular assist devices

Given the limited availability of donor hearts, ventricular assist device (VAD) therapy is fast becoming an accepted alternative treatment strategy to treat end-stage heart failure. The field of mechanical ventricular assistance is littered with novel and unique ideas either based on volume displacement or rotary pump technology, which aim to sufficiently restore cardiac output. However, only a select few have made the transition to the clinical arena. Clinical implants were initially dominated by the FDA approved volume displacement Thoratec HeartMate I, IVAD, and PVAD, whilst Berlin Heart's EXCOR, and Abiomed's BVS5000 and AB5000 offered suitable alternatives. However, limitations associated with an inherently large size and reduced lifetime of these devices stimulated the development and subsequent implantation of rotary blood pump (RBP) technology. Almost all of the reviewed RBPs are clinically available in Europe, whilst many are still undergoing clinical trial in the USA. Thoratec's HeartMate II is currently the only rotary device approved by the FDA, and has supported the highest number of patients to date. This pump is joined by MicroMed Cardiovascular's Heart Assist 5 Adult VAD, Jarvik Heart's Jarvik 2000 FlowMaker and Berlin Heart's InCOR as the axial flow devices under investigation in the USA. More recently developed radial flow devices such as WorldHeart's Levacor, Terumo's DuraHeart, and HeartWare's HVAD are increasing in their clinical trial patient numbers. Finally CircuLite's Synergy and Abiomed's Impella are two mixed flow type devices designed to offer partial cardiac support to less sick patients. This review provides a brief overview of the volume displacement and rotary devices which are either clinically available, or undergoing the advanced stages of human clinical trials.

Current trends in implantable left ventricular assist devices

The shortage of appropriate donor organs and the expanding pool of patients waiting for heart transplantation have led to growing interest in alternative strategies, particularly in mechanical circulatory support. Improved results and the increased applicability and durability with left ventricular assist devices (LVADs) have enhanced this treatment option available for end-stage heart failure patients. Moreover, outcome with newer pumps have evolved to destination therapy for such patients. Currently, results using nonpulsatile continuous flow pumps document the evolution in outcomes following destination therapy achieved subsequent to the landmark Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure Trial (REMATCH), as well as the outcome of pulsatile designed second-generation LVADs. This review describes the currently available types of LVADs, their clinical use and outcomes, and focuses on the patient selection process.

Transapical miniaturized ventricular assist device: design and initial testing

BACKGROUND

Left ventricular assist devices are increasingly used to treat patients with advanced and otherwise refractory heart failure as bridge to transplant or destination therapy. We evaluated a new miniaturized left ventricular assist device that requires minimal surgery for implantation, potentially allowing implantation in earlier stage heart failure.

METHODS

HeartWare (Miami Lakes, Fla) developed transapical miniaturized ventricular assist device. Acute (n = 4), 1-week (n = 2), and 30-day (n = 4) bovine model experiments evaluated hemodynamic efficacy and biocompatibility of the device, which was implanted through small left thoracotomy with single insertion at apex of left ventricle without cardiopulmonary bypass. The device outflow cannula was positioned across the aortic valve. The international normalized ratio was maintained between 2.0 and 2.5 with warfarin. Hemodynamic, echocardiographic, fluoroscopic, hematologic, and blood chemistry measurements were evaluated.

RESULTS

The device was successfully implanted through the left ventricular apex in all 10 animals. The device was operated at 15,000 ± 1000 rpm (power consumption, 3.5-6.0 W). The device maintained normal end-organ perfusion with no significant hemolysis (0-30 mg/dL). There were no pump failures or device-related complications. At autopsy, no abnormalities were seen in endocardium, aortic valve leaflets, or aortic root. There was no evidence of thromboembolism or abnormalities in any peripheral end organs.

CONCLUSIONS

We successfully demonstrated feasibility of a novel intraventricular assist device that can be completely implanted through left ventricular apex. This transapical surgical approach eliminates needs for sternotomy, device pocket, cardiopulmonary bypass, ventricular coring, and construction of an outflow graft anastomosis.