The important development of cardiac transplantation surgery started in the 80's, has led to an increase of patients on waiting lists not followed by a parallel increase of organ donors.
For this reason, in the last ten years several mechanic circulatory supportive systems have been developed as a bridge to cardiac transplantation and are nowadays considered a possible future alternative choice to transplantation itself by means of a permanent implantation. Such systems can be classified basing upon the anatomic position of the device ((extracorporeal, paracorporeal, implantable)) position respect to circulatory system ((in series or in parallel)); kind of flux provided ((axial or centifugal propulsion, not pulsating; or by diaphragm or sack, pulsating)); kind of energy used ((electrical, electromagnetical, pneumatical)).
Extracorporeal devices used since a longer time need long circuits for connecting to the patients, thus limiting their movement: so they are indicated only for short time treatments. Paracorporeal systems allow a complete support with shorter connection lines but patient's mobility is limited as well. Totally implantable systems are intracorpolreal and get the energy they need by a percutaneous cable. They can rely on battery energy support, thus permitting the complete mobility of the patient, and are therefore indicated for long time treatment.
Centrifugal pumps allow several kind of assistance: right heart, left heart and total. They are made of a centrifugal, low flux pump to which an oxygenation device ((ECMO)) can be added. Total anticoagulation is required and there is a high infective risk. Furthermore, components must be frequently substituted. Patients mobilization is not allowed and so they are indicated for short time assistance ((postcardiotomy failure)).
Axial pumps are made of rotating turbines. Two models found clinical application: Jarvik 2000 and De Bakey Micromed. They consist of a turbine which sucks blood from the left ventricule apex and pump it into Aorta. Although they are very small ((and so not invasive)), they provide a non pulsating flux and require total anticoagulation. Indicated for short time assistance and clinical results have not been verified yet, because of their recent introduction in clinical practice.
Pneumatic pumps are very numerous ((Thoratec, Medos, Berlin Heart, Cardio West or total artificial heart)). They provide pulsating flux and work by compress air, which acts on a diaphragm or a sack. Blood enter ventricular cavities owing to negative pressure. They can be used as mono or biventricular assistance. They require total anticoagulation and limit patients mobility, except from the more recent Thoratec TLC II, equipped with a portable consolle. Medos and Berlin Heart include also pediatric models.
Monoventricular electric systems, namely Novacor and HeartMate, allow only left heart assistance. They are placed in an abdominal pouch and connected with the energy source by percutaneous cable; they both can get energy from a battery, thus allowing complete freedom of movement to the patient. They differ for the ventricular structure: two magnetic branches acting on a poliuretan sack for Novacor and mechanic rotatory system for HeartMate. They show thromboembolic and infectious risks and they cannot be used in small sized patients. They are the most frequently used devices in long term assistance and especially as a bridge to transplantation, although a small number of cases have been reported in which patients had been disconnected from the device after partial recovery of native heart. They cannot be used in case of biventricular failure. As regards Novacor, it seems possible to obtain a new kind of device in two years, completely different and totally implantable. The only device properly called totally artificial heart is Cardio West, actual version of Jarvik 7. Its major indications are biventricular failure and high pulmonary resistance; because of its size it's not indicated in patients showing body surface under 1.7 mq. It consists of two poliuretan ventricules, sutured at atrio‐‐ventricular valves after native ventricules removal, from which blood is pumped by pneumatic energy: therefore it provides a pulsating flux. A hundred implantation procedures show encouraging results: 70%% survival after transplantation.
At present they are studying other totally implantable artificial heart, working by electrical energy ((Abiomed and Nimbus)).