Verhandelingen - Koninklijke Academie voor Geneeskunde van België vol:66 issue:4 pages:246-52
The most important bio-prosthetic organs in cardiovascular medicine are artificial heart valve prostheses and blood pumps. Cardiac valve prostheses can be divided in 'mechanical' and 'biological' valves. Mechanical prostheses are entirely made of artificial materials and require a meticulous anticoagulation therapy. The biological heart valves or heterografts (the allo- and autografts are not considered in this issue) are made of fixed or crosslinked biological tissue and therefore anticoagulation of the patient is not necessary. Actual mechanical heart valves consist of a titanium ring in which one or more leaflets made of pyrolite carbon assure the opening and closing mechanism. Biological heart valves are made of fixed porcine aortic valves or of fixed bovine pericardium. Both tissues can be mounted on a metal frame (so-called 'stented valves') or they can lack this structure ('stentless valves'). The problem with these biological valves is the durability: during the years they start degenerating or calcifying. To prevent this, recent biological heart valves are treated with an anti-mineralisation procedure. Since recent years intense research is ongoing to develop a living heart valve by 'tissue engineering'. When the entire heart fails, and pharmacological treatment remains inadequate or a heart transplantation is not immediately possible, artificial blood pumps are implanted. In general, two categories of blood pumps can be distinguished: displacement and rotary blood pumps. Displacement pumps move a certain amount of blood by the movement of a flexible membrane. This movement is pneumatically or electrically driven and requires an extensive installation: artificial ventricles, tubing, motors, pneumatic systems and driving consoles. Examples in clinical use are: Novacor, Heart Mate, Thoratec, Medos/HIA. Recent developments focus on miniaturisation and endovascular implantation. The rotary blood pumps are well suited for these purposes. They can be either axial, diagonal or radial pumps. A promising new develoment is the Impella pump: this is an axial flow pump having a diameter of 4 mm, which is implanted, inclusive the electrical motor, in the failing heart and delivers an output of 2 to 10 liter/minute. Clinical testing of this device is ongoing.