It may be useful to make a distinction between the above two categories,even if there is in practice considerable overlap, especially as techniques advance.

A prosthesis ("fabricated substitute for a diseased or missing part of the body", according to one dictionary) we may conveniently use as a term for a substitute part which is usable in a more or less normal lifestyle.

"Artificial organs" we may regard as a more general term to include also life-saving devices such as the "iron lung" and heart-lung machine, which up to now, due to their unweildy nature, have been used primarily in hospitals or other static situations.

"Simple" mechanical prostheses (artificial limbs, teeth) have a long history. Though involving considerably more practical difficulties, we might also include in this category more recent developments such as implanted bone-reinforcements and hip-joint replacements.

Still in the "future-music" category for today's patient, but definitely practical, are "bionic" limbs with control and sensory links with the body's nervous system. Similar, if more ambitious, developments appear possible with respect to the eye.

The AbioCor implantable replacement heart (IRH) is the first available totally implantable artificial heart. We recently initiated a multicenter trial of this device in patients with severe, irreversible biventricular failure. Patients who were not candidates for other therapies, including transplantation, were evaluated. All candidates were adults with inotrope-dependent biventricular failure, whose 30-day predicted mortality was higher than 70%. A three-dimensional computerized fit study predicted fit of the AbioCor thoracic unit in all recipients. At operation, the internal battery controller and transcutaneous energy transfer unit were placed. The AbioCor thoracic unit was placed in an orthotopic position after incision of the ventricals. There were 2 intraoperative deaths (due to intraoperative bleeding or aprotinin reaction). Four late deaths were recorded, 1 from multisystem organ failure and 3 cerebrovascular accidents. Autopsy revealed thrombus on the atrial struts of the 3 patients with cerebrovascular accident. Blood pumps and valves were clean on all patients. Significant morbidity was observed, primarily related to preexisting severity of illness. However, 3 patients recovered to the point of being able to take multiple trips outside of the hospital. Two patients were discharged from the hospital, with 1 patient being discharged home for more than 7 months. No significant device malfunctions or multi-system organ failure device-related infections were noted. The AbioCor IRH may be effective therapy for patients with end-stage heart failure. Many milestones have been achieved in the initial trial in humans, including the successful discharge of a patient to home and no significant device malfunctions. The occurrence of stroke is likely related to the presence of thrombus on the atrial struts and may be decreased as these atrial struts have been removed for future clinical implants.

Feasibility studies are underway for new axial flow ventricular assist systems and with a total artificial heart (TAH). The axial flow pumps provide continuous flow from the left ventricle (LV) to the aorta; the TAH provides pulsatile flow to the pulmonary and systemic circulation. Understanding the differences between these systems is necessary for appropriate patient selection and management. We compared the Jarvik 2000 axial-flow pump and the AbioCor TAH. The Jarvik 2000 pump is placed in the LV with its outflow graft anastomosed to the aorta. This system is used for bridge-to-transplantation and destination therapy. The AbioCor TAH provides complete circulatory support. The AbioCor is used for destination therapy in patients expected to die in less than 30 days. Worldwide, 45 patients have received the Jarvik 2000 as a bridge to transplantation (n = 34) or destination therapy (n = 11) for an average duration of support of 132.8 days (5 to 853 days). In 30 bridge-to-transplantation cases, 14 patients (47%) have undergone heart transplantation, 5 (17%) continue to be supported with the Jarvik 2000 device, and 11 (37%) have died. Five of 7 patients supported by the AbioCor TAH survived beyond the perioperative period; 4 were ambulatory, 2 were discharged from the hospital, and 1 is at home 13 months after implantation. Anticoagulation therapy and infection management are necessary for both systems. Therapy with inotropic agents, vasoactive drugs, a pacemaker, and electrolyte normalization is necessary for Jarvik patients. AbioCor-supported patients do not require medications to support heart function. Vasoactive agents may be useful for controlling blood pressure.

The AbioCor is a revolutionary device. It is the only device of its kind in the clinical world. The role of the AbioCor is to provide permanent replacement of the failing heart for patients who are not transplant candidates. The clinical trial has been successful in the majority (four of seven) of patients implanted thus far. Eight more patients are required to complete the initial feasibility phase of the trial, afterwhich it remains to be seen if the trial will expand to additional patient populations. The powerful features of the pump have been demonstrated in the extremely sick group of candidates that enrolled in the study. The TET system has worked extremely well. Lastly, the milestone of discharging a patient to home on a completely internal artificial heart has been realized. The profile of CardioWest is very different from AbioCor. Although both were initially designed as permanent replacement therapies, the CardioWest has been extremely useful as a bridging device, and it may have a broader application in the future. For the CardioWest, the most favorable groups are patients with cardiomyopathy who decompensate while awaiting transplantation. On the other hand, the AbioCor is indicated in nontransplant candidates with biventricular failure who have a less than 30-day predicted survival. Proper patient selection is critical to achieving success with either device.