Progress in the development of the ABIOMED total artificial heart

The ongoing quest for the first total artificial heart as destination therapy

Many patients with end-stage heart disease die because of the scarcity of donor hearts. A total artificial heart (TAH), an implantable machine that replaces the heart, has so far been successfully used in over 1,700 patients as a temporary life-saving technology for bridging to heart transplantation. However, after more than six decades of research on TAHs, a TAH that is suitable for destination therapy is not yet available. High complication rates, bulky devices, poor durability, poor biocompatibility and low patient quality of life are some of the major drawbacks of current TAH devices that must be addressed before TAHs can be used as a destination therapy. Quickly emerging innovations in battery technology, wireless energy transmission, biocompatible materials and soft robotics are providing a promising opportunity for TAH development and might help to solve the drawbacks of current TAHs. In this Review, we describe the milestones in the history of TAH research and reflect on lessons learned during TAH development. We summarize the differences in the working mechanisms of these devices, discuss the next generation of TAHs and highlight emerging technologies that will promote TAH development in the coming decade. Finally, we present current challenges and future perspectives for the field.

Near-Field Communication Sensors

Near-field communication is a new kind of low-cost wireless communication technology developed in recent years, which brings great convenience to daily life activities such as medical care, food quality detection, and commerce. The integration of near-field communication devices and sensors exhibits great potential for these real-world applications by endowing sensors with new features of powerless and wireless signal transferring and conferring near field communication device with sensing function. In this review, we summarize recent progress in near field communication sensors, including the development of materials and device design and their applications in wearable personal healthcare devices. The opportunities and challenges in near-field communication sensors are discussed in the end.

The Biocompatibility Challenges in the Total Artificial Heart Evolution

There are limited therapeutic options for final treatment of end-stage heart failure. Among them, implantation of a total artificial heart (TAH) is an acceptable strategy when suitable donors are not available. TAH development began in the 1930s, followed by a dramatic evolution of the actuation mechanisms operating the mechanical pumps. Nevertheless, the performance of TAHs has not yet been optimized, mainly because of the low biocompatibility of the blood-contacting surfaces. Low hemocompatibility, calcification, and sensitivity to infections seriously affect the success of TAHs. These unsolved issues have led to the withdrawal of many prototypes during preclinical phases of testing. This review offers a comprehensive analysis of the pathophysiological events that may occur in the materials that compose TAHs developed to date. In addition, this review illustrates bioengineering strategies to prevent these events and describes the most significant steps toward the achievement of a fully biocompatible TAH.

Vagal Nerve Activity and the High Frequency Peak of the Heart Rate Variability

For the Quality of life (QOL) of patients with an artificial heart system, monitoring an information of the cardiovascular control system may be important. We have been evaluating the autonomic nervous system for that purpose. Recently, fluctuations in hemodynamic parameters including heart rate variability (HRV) were evaluated by means of spectral analysis and nonlinear mathematical analysis. Respiratory wavers in HRV were thought ro reflect ongoing information of the parasympathetic nerve activity. Is it true? In order to confirm this hypothesis, we recorded vagal nerve activity directly in the chronic animal experiments. Six healthy adult goats were anesthetized with Halothene inhalation and thoracotomy were performed by the fourth lib resection during mechanical ventilation. Arterial blood pressure, right and left atrial pressures were continuously monitored with the catheter insertion. Cardiac output was measured by the electromagnetic flowmeter attached to the ascending aorta. After the chest was closed, incision was made to the left neck and left vagal nerve was separated. Stainless steel electrodes were inserted into the vagal nerve and fixed by the plasticizer. After the incision was closed, the goats were transferred to the cage and extubated after waking. Hemodynamic parameters and vagal nerve activity were measured in the awake condition. The results showed that clear observation of the autonomic nerve discharges were embodied by this experimental system. The vagal nerve discharges were synchronized with heart beat and respiration. The vagal nerve tonus was significantly influenced by the hemodynamic alteration. However in some condition, the respiratory wave was not always consistent with tonus of the vagal nerve activity, thus suggesting that we should check another information to evaluate the parasympathetic tone. We must continue this study to evaluate an autonomic nerve during artifical heart circulation.

Mechanical circulatory assist device development at the Texas Heart Institute: a personal perspective

In December 2013, we performed our 1000th ventricular assist device implantation at the Texas Heart Institute. In my professional career, I have been fortunate to see the development of numerous mechanical circulatory support devices for the treatment of patients with advanced heart failure. In fact, most of the cardiac pumps in wide use today were developed in the Texas Heart Institute research laboratories in cooperation with the National Heart, Lung and Blood Institute or device innovators and manufacturers and implanted clinically at our partner St. Luke's Episcopal Hospital. My early involvement in this field was guided by my mentors, Dr Michael E. DeBakey and, especially, Dr Denton A. Cooley. Also, many of the advances are directly attributable to my ongoing clinical experience. What I learned daily in my surgical practice allowed me to bring insights to the development of this technology that a laboratory researcher alone might not have had. Young academic surgeons interested in this field might be well served to be active not only in laboratory research but also in clinical practice.

The AbioCor totally implantable replacement heart

The AbioCor artificial heart (Abiomed, Inc., Danvers, MA) represents the latest technologic advancement in the quest for a total heart replacement system. The AbioCor is an electric heart with fully implantable components. The Food and Drug Administration approved a clinical trial in January 2001. The clinical trial was designed as an initial feasibility study to determine the safety and efficacy of this first generation system. The study criteria include end-stage adult heart failure patients who are not transplant candidates. These patients have biventricular failure with a predicted 30-day life expectancy of less than 30%. On July 2, 2001 the first AbioCor device was implanted. Six other patients have undergone implantation to date. Four of the seven have been successful as defined by the study parameters of 60-day survival with improved quality of life. Two patients were discharged from the hospital. Outpatient activities were possible in four patients. There have been no device malfunctions and no device-related infections. The trial is active and enrollment is ongoing.

Baseline hemodynamic and echocardiographic indices in anesthetized calves

The experimental calf model is used to assess mechanical circulatory support devices and prosthetic heart valves. Baseline indices of cardiac function have been established for the normal awake calf but not for the anesthetized calf. Therefore, we gathered hemodynamic and echocardiographic data from 16 healthy anesthetized calves (mean age, 189.0 +/- 87.0 days; mean body weight, 106.9 +/- 32.3 kg) by cardiac catheterization and noninvasive echocardiography, respectively. Baseline hemodynamic data included heart rate (65 +/- 12 beats per minute), mean aortic pressure (113.5 +/- 17.4 mm Hg), left ventricular end-diastolic pressure (16.3 +/- 38.9 mm Hg), and mean pulmonary artery pressure (21.7 +/- 8.3 mm Hg). Baseline two-dimensional echocardiographic data included left ventricular systolic dimension (3.5 +/- 0.7 cm), left ventricular diastolic dimension (5.6 +/- 0.8 cm), end-systolic intraventricular septal thickness (1.7 +/- 0.2 cm), end-diastolic intraventricular septal thickness (1.2 +/- 0.2 cm), ejection fraction (63 +/- 10%), and fractional shortening (37 +/- 10%). Doppler echocardiography revealed a maximum aortic valve velocity of 0.9 +/- 0.5 m/s and a cardiac index of 3.7 +/- 1.1 L/minute/m2. The collected baseline data will be useful in assessing prosthetic heart valves, cardiac assist pumps, new cannulation techniques, and robotics applications in the anesthetized calf model and in developing calf models of various cardiovascular diseases.

Biventricular mechanical replacement

The role of biventricular mechanical support (assist or replacement) is important for the management of severe biventricular cardiac failure. One only has to look at the role of cardiac transplantation to realize the benefit of a natural therapy to end-stage heart disease. Although the technology today is not that different from the technology that existed a decade ago (ie, BioMedicus, BVS 5000, Thoratec, CardioWest), the application of it and the experience gained by it have allowed surgeons to improve the chances of a positive outcome. In terms of new technologies for biventricular mechanical support, the totally implantable versions of a VAD (eg, Thoratec IVAD) or the totally implantable TAH (eg, AbioCor) are promising technologies that add to the spectrum of devices as destination therapy or alternatives to transplantation. And lastly, the role of the Berlin Heart as a tool for the management of biventricular failure in pediatric patients may be realized in the United States in the near future. In conclusion, the treatment of biventricular failure (acute or chronic) with assist or replacement technologies has gained widespread acceptance in the medical and surgical communities. It is now time to use these technologies wisely in an effort to treat the worldwide epidemic of congestive heart failure.

Prologue: ventricular assist devices and total artificial hearts. A historical perspective

In the 1960s, when LVADs and TAHs were introduced into clinical use, researchers estimated that, with this technology, the problem of heart failure could be solved within 20 years. Unfortunately, the evolution of these devices has taken much longer than anticipated. Nevertheless, significant advances have been achieved in both cardiac assistance and replacement, and today's cardiac surgeons have a wide range of devices from which to choose (Table 4). This progress has largely been due to the support of the NHLBI, especially the Devices and Technology Division headed by John Watson, and of the devoted commitment of the investigators. Because of the long-term commitment required for both basic and clinical research, commercial medical technology companies are unable to assume this burden. Advances in mechanical circulatory support and replacement have benefited numerous patients worldwide who would otherwise have died of heart failure, and devices now exist for use as bridges to recovery, bridges to transplant, and destination therapy. The current challenge is to refine what we have and to apply these technologies to broader patient populations with maximal safety and at a reasonable cost.

The AbioCor totally implantable replacement heart

An artificial heart with adequate circulatory support and an acceptable quality of life remains one of the holy grails of heart failure medicine and surgery. The totally implantable AbioCor is powered electrically via an external power source and has no skin-piercing cables. To date, seven critically ill patients with end-stage heart failure have been implanted with it. Four patients survived beyond 2 months, and two patients were discharged from the hospital. Both enjoyed improved quality of life with frequent social excursions; another patient is about to be discharged. While three patients died, early trials suggest that this device holds promise.

Recent progress in artificial organ research at Tohoku University

Tohoku University has developed various artificial organs over the last 30 years. Pneumatic driven ventricular assist devices with a silicone ball valve have been designed by the flow visualization method, and clinical trials have been performed in Tohoku University Hospital. On the basis of these developments, a pneumatic driven total artificial heart has been developed and an animal experimental evaluation was conducted. The development of artificial organs in Tohoku University has now progressed to the totally implantable type using the transcutaneous energy transmission system with amorphous fibers for magnetic shielding. Examples of implantable systems include a vibrating flow pump for ventricular assist device, an artificial myocardium by the use of shape memory alloy with Peltier elements, and an artificial sphincter for patients with a stoma. An automatic control system for artificial organs had been developed for the ventricular assist devices including a rotary blood pump to avoid suction and to maintain left and right heart balance. Based upon the technology of automatic control algorithm, a new diagnostic tool for evaluating autonomic nerve function has been developed as a branch of artificial organ research and this new machine has been tested in Tohoku University Hospital. Tohoku University is following a variety of approaches aimed at innovation in artificial organs and medical engineering fields.

Mechanical circulatory support--a long and winding road

The highly public reintroduction of the total artificial heart last year has prompted renewed interest in mechanical circulatory support systems for the treatment of end-stage heart disease.

Infection and thrombosis in total artificial heart technology: past and future challenges--a historical review

On the basis of animal testing and a single clinical implant during the 1960s, development of the total artificial heart (TAH) began in earnest in the 1970s. The goal was to produce a pump that could treat biventricular heart failure or any other condition that necessitated removal of the patient's native heart. The early TAHs were pneumatically powered, with externalized drivelines. After undergoing in vivo evaluation in hundreds of sheep and calves at several centers (mainly the Utah Heart Institute), these pumps were implanted in humans, initially for permanent cardiac replacement and later for bridging to transplantation. In both the in vivo experimental setting and the clinical setting, infection and thrombosis were problematic, infection being encountered much more frequently than thrombosis in clinical cases. To minimize these problems, four research groups, funded by NIH, began in 1988 to develop permanent, transcutaneously powered, totally implantable, electromechanical TAHs. For the first time, TAH technology was able to minimize infection and thrombosis, as confirmed by current in vivo studies. These new TAHs will undergo preclinical, pre-IDE studies this year and clinical trials in the near future. This article briefly reviews the evolution of TAH technology, with an emphasis on the prevention and management of infection and thrombosis.

Totally implantable ventricular assist system that can increase brain blood flow

In the clinical usage of the ventricular assist device (VAD), multiple organ failure becomes an important problem. To improve the clinical record of the VAD, another organ function may be vitally important. For that reason, we have been developing a VAD system aiming at improving another organ's function. Development of the vibrating flow pump (VFP), which can generate a very unique flow pattern from 10 Hz to 50 Hz, was ongoing in our Institute. In order to evaluate brain blood flow and oxygen consumption, HbO2 was measured with a NIRO monitoring device in healthy adult goats. Four goats were anesthetized with halothane inhalation; then left thoracotomy was performed for the left heart bypass. HbO2 of the brain was measured by recording of the hemodynamic variables during left heart assistance with the VFP system. During left heart bypass with the VFP system, hemodynamic parameters stayed within normal range, and satisfactory pump output was easily obtained. Pump output stayed within 20-40% bypass to evaluate the effect of high frequency oscillated assist flow on brain blood flow during the same cardiac output. Interesting results were observed during the experiments. During 30 Hz drive of the VFP left heart assistance, HbO2 suggested that brain blood flow significantly increased compared with another drive frequency assistance during the same total cardiac output. These results suggest that we can control the brain blood flow with a totally implantable VAD system such as the VFP system.

Future directions of cardiac assistance

During the past decade, mechanical circulatory support has gained increased acceptance as a treatment for patients with severe heart failure who are unresponsive to conventional treatment. Steady progress has been made with respect to technology, patient selection, and postoperative management. Currently, a wide array of circulatory assist pumps offers various levels of assistance and degrees of postoperative mobility. These devices not only save lives (lowering the mortality of heart transplant candidates by 55%) but, in some long-term bridge-to-transplant cases, permit hospital discharge and cardiac rehabilitation. More than 4000 patients have been supported by long-term assist pumps worldwide. In addition to being used for bridging to transplantation or bridging to the use of some other bridging device, long-term circulatory assist devices are being evaluated as bridges to recovery or alternatives to transplantation in selected patients with severe heart failure. Moreover, several total artificial hearts have shown considerable potential in calves and will soon undergo clinical trials aimed at permanent heart replacement. Eventually, as cardiac support or replacement devices become smaller, more durable, and less obtrusive, they may become as conventional and commonplace as pacemakers are today.

Peripheral vascular resistances during total left heart bypass with an oscillated blood flow

For development aimed at a totally implantable type ventricular assist device (VAD), the vibrating flow pump (VFP) has been developed at Tohoku University. A transcutaneous energy transmission system (TETS) using amorphous fibers was developed to power the totally implantable VAD system. The VFP works at a high frequency compared to that of a natural heart of a biological system. It is a frequency of 10-50 Hz. In this research, animal experiments with left heart bypass were carried out with healthy adult goats. For comparison between nonpulsatile flow and oscillated flow, a rotary pump (RP) and the VFP were used in the experiments. For the achievement of total left heart bypass, left ventricular approaches were carried out, and blood was pumped from the left ventricle to the descending aorta. Adequate support of the left heart was provided by both pumps. In terms of the results, the vascular resistances tended to decrease during the use of both pumps during 100% bypass driving. When we compared these pumps at the same flow rate, the resistances during RP driving were significantly smaller than those during VFP driving. These results may suggest that the influences of the VFP upon the peripheral vessels may be relatively small compared to those of the RP. This may be an important result when a stable hemodynamic condition is required during artificial circulation. The VFP was considered as a candidate for a totally implantable VAD as a result.

Heart booster: a pericardial support device

BACKGROUND

Congestive heart failure is a pervasive disease afflicting millions of people. For many, their quality of life can be significantly improved by a pericardial device that can enhance cardiac output without the added risk of thromboembolism associated with direct blood contact.

METHODS

A cardiac assist device with tubular elements is wrapped around the heart. Fluid is pumped into and out of the wrap causing contraction and dilation of its circumference. This contracting and relaxing action generates cardiac assistance without the need to contact blood. In vitro characterization and in vivo studies in calves were conducted to demonstrate the characteristics of the device.

RESULTS

In vitro characterization with the device wrapped around one-half of a ventricle to simulate left ventricular support demonstrated outputs of 6.5 L/min at physiological afterloads. In vivo studies in calves demonstrated both cardiac output and afterload enhancements when the device is activated.

CONCLUSIONS

This study provides a first demonstration of a device that provides cardiac support by a contraction and relaxation scheme with the device wrapped around the epicardium of the heart. The main feature of this actuation method is the potential for building a small device for implantation without blood contact.

Ultracompact, completely implantable permanent use electromechanical ventricular assist device and total artificial heart

An ultracompact, completely implantable permanent use electromechanical ventricular assist device (VAD) and total artificial heart (TAH) intended for 50-60 kg size patients have been developed. The TAH and VAD share a miniature electromechanical actuator that comprises a DC brushless motor and a planetary roller screw. The rotational force of the motor is converted into the rectilinear force of the roller screw to actuate the blood pump. The TAH is a one piece design with left and right pusher plate type blood pumps sandwiching an electromechanical actuator. The VAD is one half of the TAH with the same actuator but a different pump housing and a backplate. The blood contacting surfaces, including those of the flexing diaphragm and pump housing, of both the VAD and TAH were made of biocompatible polyurethane. The diameter, thickness, volume, and weight of the VAD are 90 mm, 56 mm, 285 cc, and 380 g, respectively, while those of the TAH are 90 mm, 73 mm, 400 cc, and 440 g, respectively. The design stroke volume of both the VAD and TAH is 60 cc with the stroke length being 12 mm. The stroke length and motor speed are controlled solely based on the commutation signals of the motor. An in vitro study revealed that a maximum pump flow of 7.5 L/min can be obtained with a pump rate of 140 bpm against a mean afterload of 100 mm Hg. The power requirement ranged from 4 to 6 W to deliver a 4-5 L/min flow against a 100 mm Hg afterload with the electrical-to-hydraulic efficiency being 19-20%. Our VAD and TAH are the smallest of the currently available devices and suitable for bridge to transplant application as well as for permanent circulatory support of 50-60 kg size patients.

A future prediction type artificial heart system

The demand of the biological system needs to be predicted to consider the quality of life (QOL) of a patient with an artificial heart system. The purpose of this study was the prediction of the imminent cardiac output and the predictive control for an artificial heart. For that purpose, autonomic nerve information was applied in this study. Nervous sympathicus action potentials were measured, and a prediction function of cardiac output was made using the sympathetic tone and preload and after-load measurement with multiple regression analysis. The predicted value showed significant correlation with the measured value after 2.9 s. Currently, however, long-term instrumentation of the nervous sympathicus potential is difficult. Thus, hemodynamic fluctuations, which recently have attracted attention, were used in this study. A prediction function using the Mayer wave, which represented nervous sympathicus, was determined. As a result, mid-term prediction became possible. Furthermore, a measurement of the vagal nerve was used as a possible long-term prediction parameter. For long-term prediction, Hurst exponent analysis was used in this study. Vagal nerve discharges in the changing position showed alteration of long-term determination. In conclusion, the future prediction control of an artificial heart takes shape using these prediction functions.

In vivo evaluation of the miniaturized Gyro centrifugal pump as an implantable ventricular assist device

A miniaturized Gyro centrifugal pump has been developed to be incorporated into a totally implantable artificial heart. The Gyro PI (permanently implantable) model is a pivot bearing supported centrifugal pump with a priming volume of 20 ml. With the miniaturized actuator, the pump-actuator package has a height of 53 mm, a diameter of 65 mm, and a displacement volume of 145 ml. To evaluate the hemocompatibility and efficiency of the Gyro PI pump system, a plastic prototype (Gyro PI-601) was implanted into a bovine model as a left or right ventricular assist device (LVAD or RVAD), bypassing from the left ventricular apex to the descending aorta or from the right ventricular infundibulum to the main pulmonary artery. The calves were anticoagulated with heparin to maintain activated clotting times from 150 to 200 s. Four calves were supported for 23, 24, and 50 days in the LVAD studies, and 40 days in the RVAD study. The first calf died due to intrathoracic bleeding associated with sepsis. The second calf was euthanized for a low flow rate less than 2 L/min due to an obstructed inflow with growing pannus. The third and fourth calves were euthanized as scheduled. Renal and hepatic functions remained normal, and plasma free hemoglobin values were less than 8 mg/dL throughout the experiments. The fourth case showed flow rates of 4.83 +/- 0.57 L/min, input power of 6.16 +/- 0.49 W, and the inside temperature of the actuator of 43.5 +/- 0.52 degrees C. The pumps implanted in the fourth calf demonstrated no thrombus formation at the autopsy. These in vivo experiments revealed that the Gyro PI pump can provide adequate flow as an easily implantable, efficient, antithrombogenic, and nonhemolytic centrifugal LVAD or RVAD with miniaturized actuators.