valve replacements

Last reviewed 11/2021

General principles:

• prosthetic heart valves are either biological (bioprosthetic) or mechanical
• all mechanical valves require long-term anticoagulation
• bioprosthetic valves do not require long-term anticoagulation
• bioprosthetic valves are prone to structural valve deterioration over time
• most patients over 65 years (aortic) or 70 years (mitral) of age receive a bioprosthesis
• NICE no longer recommends routine antibiotic prophylaxis against endocarditis for most patients with prosthetic heart valves

Despite the decline in rheumatic valve disease in the UK, surgical replacement of diseased heart valves remains an important and effective treatment, most commonly for degenerative or congenital valve disease

• commonest valves to be replaced are the aortic (AVR) and mitral (MVR).

Prosthetic valves

• prosthetic heart valves are made either from non biological materials, mostly metals, termed mechanical valves, or from mammalian tissues, usually bovine or porcine, and are termed biological or bioprosthetic valves
  • mechanical valves:
    
    
    • bileaflet - account for > 95% of all mechanical valves implanted - they are quiet, mechanically stable and relativelively haemodynamically efficient
      
      
    • single tilting disc - these have a single circular occluder controlled by a metal strut
      
      
    • ball and cage - now rarely implanted, haemodynamically the least efficient with a high tendency to forming blood clots, so the patient must have a high degres of anticoagulations, usually with a target INR of 2.5-3.5
      
      
  • biological valves
    
    
    • bioprostheses can either be stented (mounted on a fabric covered metal frame) or stentless - these are made from glutaraldehydre treated procine leaflet tissue or bovine pericardium and treated to prevent calcification
      
      
    • stented pericardial valves have a better haemodynamic performance than stented procirne vlaves, epsecially in smaller sizes (< 21 mm)
      
      
    • stentless bioprostheses are contstructed from porcine aortic valves and have shown to have better haemodynamic efficciency than stented valves and mechanical prostheses - this is likely to be related to the ability to implant a larger prosthesis and lack of support structure
      
      
    • homografts (from human cadavers) account for about 2% of valves implanted and are used in those with complicated aortic valve endocarditis and as aortic/pulmonary valve substitutes in young patients - they are prone to structural valve deterioration and their implantation is more complex than stented valves

Reference:

• 1) BHF (factfile May 2009). Prosthetic heart valves.