The AbioCor totally implantable replacement heart

Fundamental analysis and development of the current and voltage control method by changing the driving frequency for the transcutaneous energy transmission system

We have been developing transcutaneous energy transmission system (TETS) for a ventricular assist device, shape memory alloy (SMA) fibered artificial organs and so on, the system has high efficiency and a compact size. In this paper, we summarize the development, design method and characteristics of the TETS. New control methods for stabilizing output voltage or current of the TETS are proposed. These methods are primary side, are outside of the body, not depending on a communication system from the inside the body. Basically, the TETS operates at the fixed frequency with a suitable compensation capacitor so that the internal impedance is minimalized and a flat load characteristic is obtained. However, when the coil shifted from the optimal position, the coupling factor changes and the output is fluctuated. TETS has a resonant property; its output can be controlled by changing the driving frequency. The continuous current to continuous voltage driving method was implemented by changing driving frequency and setting of limitation of low side frequency. This method is useful for battery charging system for electrically driven artificial hearts and also useful for SMA fibered artificial organs which need intermittent high peak power comsumption. In this system, the internal storage capacitor is charged slowly while the fibers are turned off and discharge the energy when the fibers are turned on. We examined the effect of the system. It was found that the size and maximum output of the TETS would able to be reduced.

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.

Past and present of cardiocirculatory assist devices: a comprehensive critical review

During the last 20 years, the management of heart failure has significantly improved by means of new pharmacotherapies, more timely invasive treatments and device assisted therapies. Indeed, advances in mechanical support, namely with the development of more efficient left ventricular assist devices (LVADs), and the total artificial heart have reduced mortality and morbidity in patients awaiting transplantation, so much so, that LVADs are now approved of as a strategy for destination therapy. In this review, the authors describe in detail the current basic indications, functioning modalities, main limitations of surgical LAVDs, total artificial heart development, and percutaneous assist devices, trying to clarify this complex, but fascinating topic.

A new control method depending on primary phase angle of transcutaneous energy transmission system for artificial heart

A new control method for stabilizing output voltage of the transcutaneous energy transmission system for artificial heart is proposed. This method is primary side, is outside of the body, which is not depending on a signal transmission system from the implanted device. The impedance observed from primary side changes from inductive to capacitive and the output voltage decreases drastically when the output current is large and the coupling factor is higher than that of the optimal condition. In this case, the driving frequency should be changed to higher so that the phase angle of the primary impedance is zero degree. The preliminary examination showed that this control method can enhance the output voltage limit to twice and the feasibility of the primary side control.

[The results of the artificial heart]

The artificial heart is no more a dream but a reality. Over the last 40 years, many circulatory assist devices have been developed. First were the pneumatic devices, external or implantable, providing uni- or biventricular support; next were the partially implantable electromecanical devices. We went from the first generation of devices with all components (pump, energy power, control system) outside of the body to the second generation of devices with the pump and the motor implanted inside the body. Recently, the third generation of artificial hearts appeared with all components implanted inside the body allowing better mobility and quality of life. Results depend on the indication and on the kind of artificial heart implanted: partial (native heart still in place) or total (native heart removed). Essentially developped as a bridge to transplant, the artificial heart is now allowed as destination therapy.