Thomas Finocchiaro

New Linear Motor Concepts for Artificial Hearts

Total artificial hearts (TAHs), available in todays market, have the disadvantage of wear-prone components. Thus, their expectation of life is limited and the devices can only be used for temporary and not destination therapy. Durability- and wear-free operations are the critical requirements, as failure is an immediate threat to the patients life. These attributes are combined in linear motors. In this paper, the potential of a linear motor as TAHs drive is shown by a prototype. On the basis of this prototype, different motor concepts are employed. The dimensions of each concepts geometry are first roughly determined by analytical optimization, and in a second step, more finely tuned by means of finite-element (FE) calculations. After optimization, two concepts achieve the requirements, provided by the natural heart of the human body. The first motor consists of moving coils and static permanent magnets, which are embedded in a flux concentrating geometry. To avoid the disadvantage of wear-prone power connection of the coils, the other concept consists of static coils and moving permanent magnets, arranged in a Halbach array. After constructing and testing both concepts in laboratory, animal experiments will follow to identify the superior one.

System overview of the fully implantable destination therapy—ReinHeart-total artificial heart

OBJECTIVES Owing to the lack of suitable allografts, the demand for long-term mechanical circulatory support in patients with biventricular end-stage heart failure is rising. Currently available Total Artificial Heart (TAH) systems consist of pump units with only limited durability, percutaneous tubes and bulky external equipment that limit the quality of life. Therefore we are focusing on the development of a fully implantable, highly durable destination therapy total artificial heart. METHODS The ReinHeart-TAH system consists of a passively filling pump unit driven by a low-wear linear drive between two artificial ventricles, an implantable control unit and a compliance chamber. The TAH is powered by a transcutaneous energy transmission system. The flow distribution inside the ventricles was analysed by fluid structure interaction simulation and particle image velocimetry measurements. Along with durability tests, the hydrodynamic performance and flow balance capability were evaluated in a mock circulation loop. Animal trials are ongoing. RESULTS Based on fluid structure interaction simulation and particle image velocimetry, blood stagnation areas have been significantly reduced. In the mock circulation loop the ReinHeart-TAH generated a cardiac output of 5 l/min at an operating frequency of 120 bpm and an aortic pressure of 120/80 mmHg. The highly effective preload sensitivity of the passively filling ventricles allowed the sensorless integration of the Frank Starling mechanism. The ReinHeart-TAH effectively replaced the native hearts function in animals for up to 2 days. CONCLUSIONS In vitro and in vivo testing showed a safe and effective function of the ReinHeart-TAH system. This has the potential to become an alternative to transplantation. However, before a first-in-man implant, chronic animal trials still have to be completed.

Design and evaluation of a hybrid mock circulatory loop for total artificial heart testing

Aims A hybrid mock circulatory loop (MCL) was developed for total artificial heart (TAH) performance evaluation. The hybrid MCL consists of hydraulic hardware components and a software computer model. Design The hydraulic components are divided into the systemic and pulmonary circulation, each of which includes electrically controlled compliances, resistors, and a venous volume which can be adjusted for a wide range of physiological and pathological conditions. The software model simulates the baroreflex autoregulatory response by automatically adjusting the hydraulic parameters according to changes of condition in the MCL. Results The experimental results demonstrated a good representation of the human cardiovascular system and the capability of real-time variation of physiological and pathological conditions. The functionality of the baroreflex autoregulatory mechanism was evaluated by simulation of a postural change. Conclusions The hybrid MCL that we developed allows variable and continuous in vitro evaluation of mechanical circulatory support devices in TAH configuration and particularly their control algorithms in response to various cardiovascular conditions. The system has been built in a modular configuration to allow testing of different types of devices and thus provides a valuable test platform prior to animal experiments.

Numerical computation can save life: FEM simulations for the development of artificial hearts

Cardiovascular diseases are the major cause of death worldwide. In conjunction with the restricted heart transplants due to the limited number of donor hearts, artificial hearts (AH) are the only therapy available for terminal heart diseases. Starting from the first design of an AH to its implantation into a human body, the AH has to pass several clinical trials, which result in redesigns and optimizations respectively. During this process, the dimensions, the weight and the required electromagnetic forces of the AH as well as blood damage, caused e.g. by shear forces or overheating, have to be considered. Thus, a coupling of analytical and numerical approaches permits an accurate design process to investigate force characteristics and losses of the drive. This contribution will give an example of an existing AH and provides exemplary the adoption of analytical and numerical approaches for the design of an AH developed by the authors. The presented heart prototype was already in operation during clinical animal tests.

Image based evaluation of mediastinal constraints for the development of a pulsatile total artificial heart.

BackgroundGood anatomical compatibility is an important aspect in the development of cardiovascular implants. This work analyzes the interaction of the pump unit of an electrically driven pulsatile Total Artificial Heart (TAH) and the mediastinum. For an adequate compliance, both overall dimensions and alignment of inlets and outlets must be matched.MethodsCross-sectional medical image data of 27 individuals, including male and female patients suffering from end stage heart failure, was segmented and reconstructed to three dimensional (3D) surface models. Dimensions and orientations of relevant structures were identified and analyzed. The TAH surface model was virtually placed in orthotopic position and aligned with atrioventricular valves and big vessels. Additionally seven conventional cadaver studies were performed to validate different pump chamber designs based on virtual findings. Thereby 3D-coordinates were captured and introduced to the virtual environment to allow quantitative comparison between different individuals.ResultsSpatial parameters varied more in male patients with higher values if heart failure persists. Good correlation of the virtual analysis both to literature data and conventional cadaver studies could be shown. The full data of the 27 individuals as well as the summarized values found in literature are enclosed in the appendix. By superimposing the TAH-volume model to the anatomy, various misalignments were found and the TAH-design was adjusted.ConclusionsVirtual fitting allows implant design adjustments in realistic anatomy which has not been influenced by thoracotomy. Higher numbers of relevant individuals can be reasonably investigated in the virtual environment and quantitatively correlated. Using this approach, conventional cadaver studies can be significantly reduced but not obviated, due to the unavailable haptic feedback and immobility of potentially compressed structures.

Paving the way for destination therapy of end-stage biventricular heart failure: the ReinHeart total artificial heart concept.

The rising demand for cardiac transplantation and the steady decline in the number of instances of organ donation pose a serious challenge to physicians dealing with biventricular end-stage heart failure. Total artificial heart (TAH) therapy is therefore an alternative of growing importance. Three systems are currently available: The SynCardia-TAH (SynCardia Systems, Inc., Tucson, AZ, USA), the AbioCor-TAH (Abiomed, Inc., Danvers, MA, USA) and since recently the CARMAT-TAH (Carmat SA, Velizy Villacoublay, France). The ‘SynCardia’ is the only TAH system widely available. In addition to being a bridge to transplant [1, 2], the US Food and Drug Administration (FDA) recently approved a Humanitarian Use Device designation for the SynCardia-TAH for its use for destination therapy (DT) in patients not eligible for transplantation [3]. The limitations of this technology are mechanical parts that are prone to wear and tear, the need for percutaneous tubes and dependence on a permanent external driver. The ‘AbioCor-TAH’ was the first totally implantable, electrically driven TAH, designed as an alternative to cardiac transplantation. Although approved under the Humanitarian Device Exemption program in 2006, the device is currently not implanted due to its limited clinical success [4]. Finally, the ‘CARMAT’ is a fully implantable, electrohydraulically driven, pulsatile flow device with four bioprosthetic valves. Its artificial ventricles consist of processed bioprosthetic pericardial tissue and expanded polytetrafluorethylene [5]. The first-in-man implant was performed in 2013. The duration of support was 74 days. The feasibility trial is still ongoing. Durability and maintenance-free operation are essential requirements incorporated into any TAH design to facilitate long-term support. Reliable operation and broad applicability depend on small dimensions of the pump unit, low weight, low thermal losses, minimal haemolysis and thrombogenicity, sufficient pumping capacity and redundancy in all possible system components. These requirements are addressed by the ‘ReinHeart’ (Fig. 1). This is an electrically driven TAH currently being developed on this basis by our institutions. It is designed as an alternative to heart transplantation and aimed to support patients for at least 5 years. The size of the pump unit and the orientation of the inand outlets have been optimized according to anatomical and virtual fit studies [6]. A first major characteristic of the ReinHeart concept is the application of a linear motor concept that diminishes the need for wearprone components such as ball-bearings, gears and lubricants, increasing the durability and reliability of the pump unit. The linear motor is directly connected to a left and a right pusher plate, guided by a single linear bearing. The pusher plates are actuated in an alternating way, pumping the blood out of the chambers in a physiological sinusoidal pattern. The chambers consist of highly biocompatible transparent methacrylate–acrylonitrile–butadiene– styrene thermoplastic copolymer. Four mechanical valves (St Jude Medical, Inc.; St Paul, MN, USA) facilitate unidirectional blood flow. A second major characteristic of the ReinHeart is that the pump chambers are not mechanically attached to the pusher plates, enabling a preload sensitive filling and consequently ejection of the ventricles. This allows a robust implementation of a starling-like behaviour similar to the natural heart. In contrast to the AbioCor and the CARMAT-TAHs, vulnerable pressure sensors are not required for this purpose. Depending on operational frequency and preload, the artificial ventricles can generate a pump flow of up to 7.5 l/min. Figure 2 gives an overview of the system components. The implanted components are the pump unit, an implantable controller, a transcutaneous energy transmission (TET) system and a compliance chamber that optimizes ventricular filling. External patient equipment consists of the primary TET coil and a user interface with batteries. The TET system supports the device up to a distance of 30 mm. The batteries are charged by connecting the outer coil of the TET system and can operate the device for 45 min at full capacity. Total implantability of the system components facilitates increased patient mobility and silent operation, thus contributing to a significantly increased quality of life.

Methods of design, simulation, and control for the development of new VAD/TAH concepts / Methoden zur Konstruktion, Simulation und Regelung für die Entwicklung von neuen VAD/TAH-Konzepten

Abstract Cardiovascular diseases are a major cause of death worldwide. If medical treatments fail to restore adequate blood flow in a patient, mechanical support is needed. To date, many different types of blood pumps have been developed, but only few are clinically available. This review article describes the challenges involved in this field of research and gives an overview of the development process. Past developments as well as current and new technologies and approaches applied are summarized. Finally, a perspective for improved devices is discussed. Zusammenfassung Herz-Kreislauf-Erkrankungen sind die häufigste Todesursache weltweit. Wenn eine hinreichende Durchblutung mit konventionellen Therapien nicht gewährleistet werden kann, ist eine mechanische Kreislaufunterstützung notwendig. In der Vergangenheit wurde eine Vielzahl von Blutpumpen entwickelt, von denen sich jedoch nur wenige klinisch etabliert haben. Dieser Artikel beschreibt die Herausforderungen bei ihrer Konstruktion und gibt eine Übersicht über den Entwicklungsprozess. Bisherige Entwicklungen, aktuelle und zukünftige Technologien und Lösungsansätze werden zusammenfassend dargestellt. Abschließend werden Verbesserungspotentiale bei der Blutpumpenentwicklung diskutiert.

Mock Circulation Loop to Investigate Hemolysis in a Pulsatile Total Artificial Heart

Hemocompatibility of blood pumps is a crucial parameter that has to be ensured prior to in vivo testing. In contrast to rotary blood pumps, a standard for testing a pulsatile total artificial heart (TAH) has not yet been established. Therefore, a new mock circulation loop was designed to investigate hemolysis in the left ventricle of the ReinHeart TAH. Its main features are a high hemocompatibility, physiological conditions, a low priming volume, and the conduction of blood through a closed tubing system. The mock circulation loop consists of a noninvasive pressure chamber, an aortic compliance chamber, and an atrium directly connected to the ventricle. As a control pump, the clinically approved Medos-HIA ventricular assist device (VAD) was used. The pumps were operated at 120 beats per minute with an aortic pressure of 120 to 80 mm Hg and a mean atrial pressure of 10 mm Hg, generating an output flow of about 5 L/min. Heparinized porcine blood was used. A series of six identical tests were performed. A test method was established that is comparable to ASTM F 1841, which is standard practice for the assessment of hemolysis in continuous-flow blood pumps. The average normalized index of hemolysis (NIH) values of the VAD and the ReinHeart TAH were 0.018 g/100 L and 0.03 g/100 L, respectively. The standard deviation of the NIH was 0.0033 for the VAD and 0.0034 for the TAH. Furthermore, a single test with a BPX-80 Bio-Pump was performed to verify that the hemolysis induced by the mock circulation loop was negligible. The performed tests showed a good reproducibility and statistical significance. The mock circulation loop and test protocol developed in this study are valid methods to investigate the hemolysis induced by a pulsatile blood pump.

A Novel Total Artificial Heart for Destination Therapy: In-Vitro and In-Vivo Study.

Total Artificial Hearts (TAHs) could be used as an alternative to heart transplantation for patients with terminal heart failure. A fully implantable TAH is under development at our institute. Some critical aspects in TAH development are a) sufficient cardiac output, b) adequate left-right flow balance, c) measurement and control of pump performance and d) hemocompatibility. In this paper, the results of the validation process including in vitro, acute and first chronic in vivo experiments are presented.

Assistierte Zirkulation: ein Überblick aus klinischer Sicht / Assisted circulation: an overview from a clinical perspective

Zusammenfassung Eine höhergradige Herzinsuffizienz ist mit einer sehr schlechten Prognose behaftet. Neben medikamentös konservativen sowie operativen Ansätzen haben sich in den letzten Jahren verschiedene Formen einer assistierten Zirkulation etabliert. Kurzzeitverfahren dienen vor allem dazu, eine Akutsituation zu überbrücken. Die Systemauswahl richtet sich hierbei nach dem zu erwartenden klinischen Verlauf. Es kann auf leicht unterstützende Verfahren bis hin zu Verfahren mit einer vollständigen Übernahme der Pumpfunktion des Herzens zurückgegriffen werden. Bei jeder Form der schweren Herzinsuffizienz muss die Frage nach einer Herztransplantation als derzeitige Behandlungsoption der Wahl geklärt werden. Für eine assistierte Zirkulation im Zustand einer chronischen Herzinsuffizienz stehen Verfahren unterschiedlicher Systemgenerationen zur Verfügung. Mit pulsatilen Systemen der ersten Generation zur Assistenz des linken Ventrikels wurden Ergebnisse erzielt, welche der medikamentösen Therapie überlegen waren (REMATCH). Mit den Continuous-Flow-Systemen der zweiten Generation scheinen sich diese Ergebnisse hinsichtlich Infektionen, Thrombembolien und auch der Lebensqualität noch weiter zu verbessern. Berührungsfrei gelagerte Zentrifugalpumpen als Drittgenerationssysteme befinden sich in Evaluation. Sogenannte „total artificial hearts“ können inzwischen erfolgreich als Überbrückung bis zur Transplantation eingesetzt werden. Insgesamt ist heute eine abgestuft sichere Behandlung einer Herzinsuffizienz durch eine assistierte Zirkulation möglich. In näherer Zukunft könnten hiermit Ergebnisse erzielt werden, die an diejenigen einer Herztransplantation heranreichen. Abstract A higher grade cardiac failure is associated with poor prognosis. In addition to medical conservative treatment and traditional cardiac surgery, in the past years different forms of an assisted circulation evolved. Short-term devices serve to bridge an acute life-threatening situation. The chosen system is dependent on the anticipated clinical course. It is possible to fall back on slightly assisting techniques up to a complete takeover of the cardiac pump function. In the case of severe cardiac failure, the question for transplantation has to be addressed because transplantation is the treatment of choice to date. For an assisted circulation in cases of chronic congestive failure, devices of different generations are available. First generation pulsatile systems are used for assistance of the left ventricle and results have been shown to be superior to medical therapy (REMATCH). With second generation continuous-flow systems, results regarding infections, thromboembolism and also quality of life appear to be further improved. Contact-free centrifugal pumps as third generation systems are in clinical evaluation. So-called “total artificial hearts” are successfully used for bridge-to-transplantation. Taken together, a graded safe treatment of cardiac failure is available today. In the near future, it could be possible to reach results similar to those of cardiac transplantation.