Development of mechanical circulatory support devices at the University of Tokyo

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.

An insight into short- and long-term mechanical circulatory support systems

Cardiogenic shock due to acute myocardial infarction, postcardiotomy syndrome following cardiac surgery, or manifestation of heart failure remains a clinical challenge with high mortality rates, despite ongoing advances in surgical techniques, widespread use of primary percutaneous interventions, and medical treatment. Clinicians have, therefore, turned to mechanical means of circulatory support. At present, a broad range of devices are available, which may be extracorporeal, implantable, or percutaneous; temporary or long term. Although counter pulsation provided by intra-aortic balloon pump (IABP) and comprehensive mechanical support for both the systemic and the pulmonary circulation through extracorporeal membrane oxygenation (ECMO) remain a major tool of acute care in patients with cardiogenic shock, both before and after surgical or percutaneous intervention, the development of devices such as the Impella or the Tandemheart allows less invasive forms of temporary support. On the other hand, concerning mid-, or long-term support, left ventricular assist devices have evolved from a last resort life-saving therapy to a well-established viable alternative for thousands of heart failure patients caused by the shortage of donor organs available for transplantation. The optimal selection of the assist device is based on the initial consideration according to hemodynamic situation, comorbidities, intended time of use and therapeutic options. The present article offers an update on currently available mechanical circulatory support systems (MCSS) for short and long-term use as well as an insight into future perspectives.

The helical flow total artificial heart: implantation in goats

To realize a total artificial heart (TAH) with high performance, high durability, good anatomical fitting, and good blood compatibility, the helical flow TAH (HFTAH) has been developed with two helical flow pumps having hydrodynamic levitation impeller. The HFTAH was implanted in goats to investigate its anatomical fitting, blood compatibility, mechanical stability, control stability, and so on. The size of the HFTAH was designed to be 80 mm in diameter and 84 mm wide. The maximum output was 19 L/min against 100 mmHg of pressure head. Eight adult female goats weighting from 45 to 56.3 kg (average 49.7 kg) were used. Under the extracorporeal circulation, natural heart was removed at the atrioventricular groove and the HFTAH was implanted. The HFTAH was driven with a pulsatile mode. The 1/R control was applied when the right atrial pressure recovered. The HFTAH could be implanted with good anatomical fitting in all goats. Two goats survived for more than a week. One goat is ongoing. Other goats did not survive for more than two days with various reasons. In the goats that survived for more than a week, the hydrodynamic bearing was worn and broken, which indicated that the bearing touched to the shaft. The cause was supposed to be the influence of the sucking effect. The potential of the HFTAH could be demonstrated with this study. The stability of the hydrodynamic bearing in a living body, especially the influence of the sucking effect, was considered to be very important and a further study should be necessary.

Pulsatile driving of the helical flow pump

The helical flow pump (HFP) is newly developed blood pomp for total artificial heart (TAH). HFP can work with lower rotational speed than axial and centrifugal blood pump. It can be seen reasonable feature to generate pulsatile flow because high response performance can be realized. In this article, pulsatility of HFP was evaluated using mock circulation loop. Pulsatile flow was generated by modulating the rotational speed in various amplitude and heart rate. In the experiment, relationship between Pump flow, pump head, rotational speed amplitude, heart rate and power consumption is evaluated. As the result, complete pulsatile flow with mean flow rate of 5 L/min and mean pressure head of 100 mmHg can be obtained at ± 500 rpm with mean rotational speed of 1378 to 1398 rpm in hart rate from 60 to 120. Flow profiles which are non-pulsatile, quasi-pulsatile or complete flow can be adjusted arbitrarily. Therefore, HFP has excellent pulsatility and control flexibility of flow profile.

Total artificial heart

End-stage heart failure represents a highly morbid condition for the patient with limited treatment options. From a surgical perspective, the treatment options for effective long-term survival are usually limited to heart transplantation, heart-lung transplantation or implantation of a destination mechanical circulatory support device. Assuming an advanced heart-failure patient is indeed deemed a candidate for transplantation, the patient is subject to shortages in donor organ availability and thus possible further decompensation and potential death while awaiting transplantation. Various extracorporeal and implantable ventricular-assist devices (VADs) may be able to provide temporary or long-term circulatory support for many end-stage heart-failure patients but mechanical circulatory support options for patients requiring long-term biventricular support remain limited. Implantation of a total artificial heart (TAH) currently represents one, if not the best, long-term surgical treatment option for patients requiring biventricular mechanical circulatory support as a bridge to transplant. The clinical applicability of available versions of positive displacement pumps is limited by their size and complications. Application of continuous-flow technology can help in solving some of these issues and is currently being applied in the research towards a new generation of smaller and more effective TAHs. In this review, we discuss the history of the TAH, its development and clinical application, implications for anaesthetic management, published outcomes and the future outlook for TAHs.

Domestic animal models for biomedical research

Experimental animals in biomedical research provide insights into disease mechanisms and models for determining the efficacy and safety of new therapies and for discovery of corresponding biomarkers. Although mouse and rat models are most widely used, observations in these species cannot always be faithfully extrapolated to human patients. Thus, a number of domestic species are additionally used in specific disease areas. This review summarizes the most important applications of domestic animal models and emphasizes the new possibilities genetic tailoring of disease models, specifically in pigs, provides.

Development of normal-suction boundary control method based on inflow cannula pressure waveform for the undulation pump ventricular assist device

It is desirable to obtain the maximum assist without suction in ventricular assist devices (VADs). However, high driving power of a VAD may cause severe ventricle suction that can induce arrhythmia, hemolysis, and pump damage. In this report, an appropriate VAD driving level that maximizes the assist effect without severe systolic suction was explored. The target driving level was set at the boundary between low driving power without suction and high driving power with frequent suction. In the boundary range, intermittent mild suction may occur. Driving power was regulated by the suction occurrence. The normal-suction boundary control method was evaluated in a female goat implanted with an undulation pump ventricular assist device (UPVAD). The UPVAD was driven in a semipulsatile mode with heartbeat synchronization control. Systolic driving power was adjusted using a normal-suction boundary control method developed for this study. We confirmed that driving power could be maintained in the boundary range. Occurrences of suction were evaluated using the suction ratio. We defined this ratio as the number of suction occurrences divided by the number of heartbeats. The suction ratio decreased by 70% when the normal-suction boundary control method was used.

Preliminary study of physiological control for the undulation pump ventricular assist device

The undulation pump ventricular assist device (UPVAD) is a small implantable ventricular assist device using an undulation pump. The UPVAD can produce pulsatile flow by changing the motor rotation speed of the UPVAD. Because the undulation pump is a volume displacement type pump, the inflow sucking occurs easily. The purpose of this study is to develop a suitable control method for the UPVAD. The UPVAD inflow cannula equipped with an implantable pressure sensor was inserted into the ventricle. Therefore, pressure variation that synchronized with the natural heartbeat and negative pressure spike caused the inflow sucking were observed. By changing the motor rotation speed that responded to the inflow pressure, the UPVAD could synchronize with the natural heartbeat and the UPVAD could generate a co-pulse assist flow. The inflow sucking could be released by reducing the motor rotation speed, if the inflow sucking was detected. The newly developed control method exhibited superior characteristics than existing ones due to high immunity against pressure sensor drift. The assist flow could be increased more than 15% and the inflow sucking occurrence could be decreased with this control method. The UPVAD could generate the suitable assist flow with the developed control method.

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.

Baroreflex sensitivity of an arterial wall during rotary blood pump assistance

It is well known that the baroreflex system is one of the most important indicators of the pathophysiology in hypertensive patients. We can check the sensitivity of the baroreflex by observing heart rate (HR) responses; however, there is no simple diagnostic method to measure the arterial behavior in the baroreflex system. Presently, we report the development of a method and associated hardware that enables the diagnosis of baroreflex sensitivity by measuring the responses of both the heart and the artery. In this system, the measurements are obtained by monitoring an electrocardiogram and a pulse wave recorded from the radial artery or fingertip. The arterial responses were measured in terms of the pulse wave velocity (PWV) calculated from the pulse wave transmission time (PTT) from the heart to the artery. In this system, the HR change corresponding to the blood pressure change in time series sequence was observed. Slope of the changes in blood pressure and HR indicated the sensitivity of the baroreflex system of the heart. This system could also measure the sensitivity of the baroreflex system of an artery. Changes in the PWV in response to the blood pressure changes were observed. Significant correlation was observed in the time sequence between blood pressure change and PWV change after calculating the delay time by cross-correlation. The slope of these parameter changes was easily obtained and it demonstrated the sensitivity of the baroreflex system of an artery. We evaluated this method in animal experiments using rotary blood pump (RBP) with undulation pump ventricular assist device, and PTT elongation was observed in response to increased blood pressure with RBP assistance. Furthermore, when tested clinically, decreased sensitivity of the baroreflex system in hypertensive patients was observed. This system may be useful when we consider the ideal treatment and follow-up of patients with hypertension.