Preliminary experience with the LionHeart left ventricular assist device in patients with end-stage heart failure

Systems of conductive skin for power transfer in clinical applications

The primary aim of this article is to review the clinical challenges related to the supply of power in implanted left ventricular assist devices (LVADs) by means of transcutaneous drivelines. In effect of that, we present the preventive measures and post-operative protocols that are regularly employed to address the leading problem of driveline infections. Due to the lack of reliable wireless solutions for power transfer in LVADs, the development of new driveline configurations remains at the forefront of different strategies that aim to power LVADs in a less destructive manner. To this end, skin damage and breach formation around transcutaneous LVAD drivelines represent key challenges before improving the current standard of care. For this reason, we assess recent strategies on the surface functionalization of LVAD drivelines, which aim to limit the incidence of driveline infection by directing the responses of the skin tissue. Moreover, we propose a class of power transfer systems that could leverage the ability of skin tissue to effectively heal short diameter wounds. In this direction, we employed a novel method to generate thin conductive wires of controllable surface topography with the potential to minimize skin disruption and eliminate the problem of driveline infections. Our initial results suggest the viability of the small diameter wires for the investigation of new power transfer systems for LVADs. Overall, this review uniquely compiles a diverse number of topics with the aim to instigate new research ventures on the design of power transfer systems for IMDs, and specifically LVADs.

Left ventricular assist devices: A comprehensive review of major clinical trials, devices, and future directions

Heart failure is an increasingly prevalent medical condition associated with significant morbidity and mortality. In spite of optimal medical therapy, a large number of patients continue to deteriorate clinically and could potentially benefit from advanced therapies. While cardiac transplantation is an established therapy for end-stage heart failure, there are a limited number of donor hearts, and many patients may not be candidates. Over the past two decades, mechanical circulatory support and left ventricular assist devices (LVAD) have altered the heart failure management landscape. Herein we review the indications for LVAD implantation and how they have changed over time. We will also outline major technological evolutions in LVADs and summarize the landmark clinical trials pertaining to them. We also highlight the adverse events associated with LVADs and assess the limitations of the existing literature. Finally, we look ahead to the future of LVAD therapy for patients with advanced heart failure.

A review of implantable pulsatile blood pumps: Engineering perspectives

It has been reported that long-term use of continuous-flow mechanical circulatory support devices (CF-MCSDs) may induce complications associated with diminished pulsatility. Pulsatile-flow mechanical circulatory support devices (PF-MCSDs) have the potential of overcoming these shortcomings with the advance of technology. In order to promote in-depth understanding of PF-MCSD technology and thus encourage future mechanical circulatory support device innovations, engineering perspectives of PF-MCSD systems, including mechanical designs, drive mechanisms, working principles, and implantation strategies, are reviewed in this article. Some emerging designs of PF-MCSDs are introduced, and possible elements for next-generation PF-MCSDs are identified.

Innovations in Ventricular Assist Devices for End-Stage Heart Failure

The number of patients with end-stage heart failure (HF) continues to increase over time, but there has been little change in the availability of organs for cardiac transplantation, intensifying the demand for left ventricular assist devices (LVADs) as a bridge to transplantation. There is also a growing number of patients with end-stage HF who are not transplant candidates but may be eligible for long-term support with an LVAD, known as destination therapy. Due to this increasing demand, LVAD technology has evolved, resulting in transformative improvements in outcomes. Additionally, with growing clinical experience patient management continues to be refined, leading to iterative improvements in outcomes. With outcomes continuing to improve, the potential benefit from LVAD therapy is being considered for patients earlier in their course of advanced HF. We review recent changes in technology, patient management, and implant decision making in LVAD therapy.

Electrical power to run ventricular assist devices using the Free-range Resonant Electrical Energy Delivery system

BACKGROUND

Models of power delivery within an intact organism have been limited to ionizing radiation and, to some extent, sound and magnetic waves for diagnostic purposes. Traditional electrical power delivery within the intact human body relies on implanted batteries that limit the amount and duration of delivered power. The efficiency of current battery technology limits the substantial demands required, such as continuous operation of an implantable artificial heart pump within a human body.

METHODS

The fully implantable, miniaturized, Free-range Resonant Electrical Energy Delivery (FREE-D) system, compatible with any type of ventricular assist device (VAD), has been tested in a swine model (HVAD) for up to 3 hours. Key features of the system, the use of high-quality factor (Q) resonators together with an automatic tuning scheme, were tested over an extended operating range. Temperature changes of implanted components were measured to address safety and regulatory concerns of the FREE-D system in terms of specific absorption rate (SAR).

RESULTS

Dynamic power delivery using the adaptive tuning technique kept the system operating at maximum efficiency, dramatically increasing the wireless power transfer within a 1-meter diameter. Temperature rise in the FREE-D system never exceeded the maximum allowable temperature deviation of 2°C (but remained below body temperature) for an implanted device within the trunk of the body at 10 cm (25% efficiency) and 50 cm (20% efficiency), with no failure episodes.

CONCLUSIONS

The large operating range of FREE-D system extends the use of VAD for nearly all patients without being affected by the depth of the implanted pump. Our in-vivo results with the FREE-D system may offer a new perspective on quality of life for patients supported by implanted device.

Safety considerations for wireless delivery of continuous power to implanted medical devices

Wireless power systems for use with implants are referred to as transcutaneous energy transmission systems (TETS) and consist of an implanted secondary coil and an external primary coil along with supporting electronics. A TETS system could be used to power ventricular assist systems and eliminate driveline infections. There are both direct and indirect safety concerns that must be addressed when continuously transferring power through the skin. Direct safety concerns include thermal tissue damage caused by exposure to the electromagnetic fields, coil heating effects, and potential unwanted nerve stimulation. Indirect concerns are those caused by potential interference of the TETS system with other implanted devices. Wireless power systems are trending towards higher frequency operation. Understanding the limits for safe operation of a TETS system across a range of frequencies is important. A low frequency and a high frequency implementation are simulated to demonstrate the impact of this trend for a VAD application.

Innovative Free-range Resonant Electrical Energy Delivery system (FREE-D System) for a ventricular assist device using wireless power

Technological innovation of a smaller, single moving part has an advantage over earlier large pulsatile ventricular assist devices (VADs) prone to mechanical failure. Drivelines limit the potential for extended patient survival durations with newer pumps and act as source for infection, increased morbidity, rehospitalizations, and reduced quality of life. The Free-range Resonant Electrical Energy Delivery (FREE-D) wireless power system uses magnetically coupled resonators to efficiently transfer power. We demonstrate the efficiency over distance of this system. The experimental setup consists of an radiofrequency amplifier and control board which drives the transmit resonator coil, and a receiver unit consisting of a resonant coil attached to a radiofrequency rectifier and power management module. The power management module supplies power to the axial pump, which was set at 9,600 rpm. To achieve a seamless wireless delivery in any room size, we introduced a third relay coil. This relay coil can be installed throughout a room, whereas a single relay coil could be built into a jacket worn by the patient, which would always be within range of the receive coil implanted in the patient's body. The power was delivered over a meter distance without interruptions or fluctuations with coil, rectifier, and regulator efficiency more than 80% and overall system efficiency of 61%. The axial pump worked well throughout the 8 hours of continuous operation. Having same setup on the opposite side can double the distance. A tether-free operation of a VAD can be achieved by FREE-D system in room-size distances. It has the potential to make the VAD therapy more acceptable from the patient perspective.

Toward total implantability using free-range resonant electrical energy delivery system: achieving untethered ventricular assist device operation over large distances

Heart failure is a terminal disease with a very poor prognosis. Although the gold standard of treatment remains heart transplant, only a minority of patients can benefit from transplants. Another promising alternative is mechanical circulatory assistance using ventricular assist devices. The authors envision a completely implantable cardiac assist system affording tether-free mobility in an unrestricted space powered wirelessly by the innovative Free-Range Resonant Electrical Energy Device (FREE-D) system. Patients will have no power drivelines traversing the skin, and this system will allow power to be delivered over room distances and will eliminate trouble-prone wirings, bulky consoles, and replaceable batteries.

The need to change our objective for artificial heart development: from totally implantable permanent ventricular assist devices to wearable therapeutic ventricular assist devices

As a therapeutic VAD to be combined with drugs, apheresis, and cellular implants, it is advisable to develop a wearable VAD for less than 6 months of application. Such an example was shown by describing the therapeutic BCM Gyro centrifugal VAD.

Analysis of specific absorption rate and current density in biological tissues surrounding energy transmission transformer for an artificial heart: using magnetic resonance imaging-based human body model

The transcutaneous energy transmission system used for artificial hearts is a transmission system that uses electromagnetic induction. Use of the TETS improves quality of life and reduces the risk of infection caused by percutaneous connections. This article reports the changes in the electromagnetic effects of TETS that influence a human body when the locations of the air-core coils of the transcutaneous transformer are changed. The specific absorption rate and current density in a model consisting of a human trunk that included 24 different organs are analyzed using an electromagnetic simulator. The air-core coils are located on the pectoralis major muscle near the collarbone in model 1, whereas they are located on the axillary region of the serratus anterior muscle, which overlies the rib in model 2. The maximum current densities in models 1 and 2 are 5.2 A/m(2) and 6.1 A/m(2), respectively. The current density observed in model 2 slightly exceeds the limiting value prescribed by International Commission on Non-Ionizing Radiation Protection (ICNIRP). When the volumes of biological tissues whose current densities exceed the limiting value of current density for general public exposure are compared, the volume in model 2 (156.1 cm(3)) is found to be larger than that in model 1 (93.7 cm(3)). Hence, it is speculated that the presence of the ribs caused an increase in the current density. Therefore, it is concluded that model 1 satisfies the ICNIRP standards.

Analysis of flow patterns in a ventricular assist device: a comparative study of particle image velocimetry and computational fluid dynamics

In order to develop a diaphragm-type ventricular assist device (VAD), we studied the flow field change following structural modifications. We devised a center flow-type pump by putting a small projection on the center of the housing and/or diaphragm to provide a center in the flow field, and examined the following four types of VADs: N type without a projection, D type with a projection on the diaphragm, H type with a projection on the housing, and DH type with projections on both the diaphragm and housing. Computational fluid dynamics (CFD) was used for flow simulation. Particle image velocimetry (PIV) was also used to verify the reliability of the CFD method and to determine how the flow field changes in the presence of a projection. The results of the PIV and CFD analyses were comparable. The placement of a projection on the housing was most effective in rectifying the flow field.

Destination therapy: does progress depend on left ventricular assist device development?

The role of therapy using mechanical circulatory support devices has evolved rapidly over the last two decades. New developments in the field achieved smaller adverse events, but, currently, only minor improvements in survival were observed in published observational data. The authors discuss the development of mechanical circulatory support devices as a "destination therapy" option for patients who have end-stage heart failure and are ineligible for heart transplantation as it relates to left ventricular assist device development.

Clinical and cost-effectiveness of left ventricular assist devices as destination therapy for people with end-stage heart failure: A systematic review and economic evaluation

Objectives: The clinical and cost-effectiveness of left ventricular assist devices as destination therapy for people with end-stage heart failure is assessed through a systematic review and economic evaluation.

Methods: Systematic review was performed of randomized controlled trials, quasiexperimental studies, case series, and case studies identified through searching eighteen electronic databases, bibliographies, and consultation with experts and manufacturers. Studies assessed survival, functional capacity, and quality of life. Cost-effectiveness was assessed through a 5-year decision analytic model to estimate the incremental cost-effectiveness ratio for using left ventricular assist devices compared with usual care.

Results: Six studies met the inclusion criteria, showing that left ventricular assist devices appear beneficial, improving survival and quality of life. Adverse events are a serious concern. The economic evaluation showed that left ventricular assist devices had a cost per quality adjusted life year of £170,616. Sensitivity analysis showed that the cost-effectiveness was not sensitive to changes in costs or utility.

Conclusions: Although left ventricular assist devices appear clinically effective as destination therapy, it is unlikely they will be cost-effective unless costs decrease or the benefits of their use increase.

Report of the First U.S. Patient Successfully Supported Long Term With the LionHeart Completely Implantable Left Ventricular Assist Device System

We report our first successful long-term survivor in the United States with the LionHeart (Arrow International, Inc., Reading, PA) completely implantable left ventricular assist device system. The patient was initially deemed a poor candidate for cardiac transplantation and had inotrope-dependent, end-stage cardiac failure. The patient was supported for 13 months with this system. During this period of support, the patient returned to independent living and derived obvious benefits toward his daily activities with the completely implanted system. The device proved to be reliable during this period of support. Through lifestyle modification, the patient was ultimately deemed an appropriate candidate for heart transplantation and ultimately received successful transplantation.

Permanent use of a ventricle assist device for dilated cardiomyopathy in Friedreich's ataxia

A patient with Friedreich's ataxia was hospitalized due to dilated cardiomyopathy and heart failure. We received informed consent from the patient and his family for implantation of an implantable ventricular assist device (VAD) as permanent support. At the one-year follow-up examination, the neuromuscular symptoms had progressed no further, and he had no VAD systemic failure and complications. This is the first case report of VAD implantation in a Friedreich's ataxia patient.

Microtextured Materials for Circulatory Support Devices: Preliminary Studies

Thromboembolic events (TE) associated with circulatory support devices are a major source of mortality and morbidity. Clinically, the lowest TE rates are claimed with devices that incorporate textured blood-contacting materials. The textured materials currently used in circulatory assist devices are composed of small, attached fibers that form the boundaries of connected cavities. These cavities entrap blood components to form a "neointimal" layer, which is believed to minimize thromboembolic events. We believe that the three-dimensional surface topography of blood-contacting materials is a major controlling factor in the formation of a stable neointimal layer upon the material. Particle-cast cavities were used to form geometric features in segmented polyurethane. This microtextured material was incorporated as part of a flexible blood-contacting surface in a blood pump that was implanted as a left ventricular assist device in calves. The structure, thickness, stability, and development of the neointimal layer were then evaluated. These preliminary studies have shown that a stable neointimal layer can be formed upon the particle-cast surfaces. The results also indicate that the cavity size on the particle-cast surfaces has a significant effect on neointimal adhesion. The methods employed can be used in the design of future circulatory support devices.

Different clinical scenarios for circulatory mechanical support in acute and chronic heart failure

Chronic heart failure (HF) is a leading cause of death in developed countries. Over the last 2 decades, mechanical circulatory support (MCS) devices have steadily evolved in the clinical management of end-stage HF and have emerged as a standard of care for the treatment of acute and chronic HF refractory to conventional medical therapy. Possible indications for using MCS are acute cardiogenic shock, as a bridge to transplantation, as a bridge to recovery, and more recently, as destination therapy in dilated cardiomyopathy, of either ischemic or idiopathic etiology. We reviewed the different clinical scenarios in which we think there are currently indications to implant different kinds of MCS systems.

Temporary or permanent support and replacement of cardiac function

Cardiac assist devices are classified into the traditional engineering categories of displacement and rotary pumps. Clinical use and indications of the various pump categories are outlined and a detailed description of the currently available systems is given. The first section deals with extracorporeal as well as implantable ventricular assist devices of the displacement type and is followed by a section on current developments in the field of total artificial hearts. The latter part of the article covers the rotary pump category from cardiopulmonary bypass applications to implantable systems, including specific design aspects of radial, diagonal and axial pumps.

The Status of Failure and Reliability Testing of Artificial Blood Pumps

Artificial blood pumps are today's most promising bridge-to-transplant, bridge-to-recovery, and destination therapy solutions for patients with congestive heart failure. There is a critical need for increased reliability and safety as the next generation of artificial blood pumps approach final development for long-term destination therapy. To date, extensive failure and reliability studies of these devices are considered intellectual property and thus remain unpublished. Presently, the Novacor N100PC, Thoratec VAD, and HeartMate LVAS (IP and XVE) comprise the only four artificial blood pumps commercially available for the treatment of congestive heart failure in the United States. The CardioWest TAH recently received premarket approval from the US Food and Drug Administration. With investigational device exemptions, the AB-180, AbioCor, LionHeart, DeBakey, and Flowmaker are approved for clinical testing. Other blood pumps, such as the American BioMed-Baylor TAH, CorAide, Cleveland Clinic-Nimbus TAH, HeartMate III, Hemadyne, and MagScrew TAH are currently in various stages of mock loop and animal testing, as indicated in published literature. This article extensively reviews in vitro testing, in vivo testing, and the early clinical testing of artificial blood pumps in the United States, as it relates to failure and reliability. This detailed literature review has not been published before and provides a thorough documentation of available data and testing procedures regarding failure and reliability of these various pumps.

Destination Therapy with Ventricular Assist Devices

Despite extensive research and great strides over the past 40 years, the ideal permanent mechanical assist device remains elusive. The incidence of heart failure is increasing, and the number of heart transplants has remained constant. The HeartMate and Novacor are two pulsatile, long-term ventricular assist devices (VADs) commonly used as a bridge to transplantation. Randomized Evaluation of Mechanical Assistance in the Treatment of Congestive Heart Failure is a randomized study of device therapy in heart failure with treatment either with device (HeartMate) therapy or maximal medical therapy which was recently completed and demonstrated a Kaplan-Meier survival rate at 1 year of 52% for the device group compared to 25% in the medical therapy group. The TCI HeartMate is the only device approved for destination therapy, while others such as the Novacor device are in the process of evaluation. Most of these devices are still plagued by mechanical problems, bleeding, thromboembolism and infection. Other promising new devices include smaller VADs using impeller pump technology, such as the Arrow LionHeart, Micromed Debakey pump and Jarvik 2000 pump. The CardioVAD is an interesting chronically implantable balloon pump inserted into the descending thoracic aorta. While experience with the newer implantable pumps is growing, most of them require some manipulation of the heart perioperatively, in addition to anticoagulation postoperatively and careful monitoring for complications and infection.