VALVE PROSTHESIS

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PROSTHESES PARAMETERS

Prothesis Dysfunction

MECHANICAL PROSTHESeS

ANTICOAGULATION

BIOLOGICAL PROSTHESeS

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PARAMETERS OF VALVE PROSTHESES

Tissue Annulus Diameter (TAD)

• The valve label of the trade name and a number indicating the valve size (in millimeters)
• Represents the outer diameter of the valve housing/stent  tissue annulus diameter

Internal Orifice Diameter (IOD)

• It is smaller than the labeled valve size
• Used for the new bioprostheses designed for supra-annular implantation as both the sewing ring and  housing/stent is placed above the patient’s annulus and so the IOD is equal to the TAD

External Sewing Ring Diameter (ESRD)

• The whole artificial valve diameter is larger for several millimetres (the thickness of the sewing ring is added) 

​PROSTHESIS DIAMETERS

IOD Internal  Orifice Diameter
TAD  Tissue Annulus Diameter
ESRD External Sewing Ring Diameter

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​Implantation PositionS

Intra-annular Position

• ESRD is equal to the annulus diameter (TAD)
• Disadvantageous with a narrow annulus because the valve housing and its sewing ring occlude an important portion of the patient’s valve orifice

Intra-supra-annular Position:

• The sewing ring is placed above the annulus but the valve housing remains intra-annular

Supra-annular Position

• Both the sewing ring and the valve housing/stent are located above the annulus
• This allows implantation of a valve with a much larger orifice area offering better haemodynamic parameters 
• Examples: CarboMedics Top Hat, Sorin Bicarbon Overline, and Medtronic Advantage Supra

Implantation
a. intraannulary (sewing ring inside of
    the aortic annulus)





b. intra-supra-annulary (sewing ring is
    placed supraannulary, stent  is located
    intraannulary)




c. supra-anulary (both sewing ring and 
    stent are placed supraannulary)

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​PROSTHESIS ORIFICE AREAS

GOA, COA, and EOA of 
Left Column Bileaflet valves 
Centre column: Tilting mono-discs
Right column:Bioprostheses

Geometric Orifice Area (GOA)

• The whole inner area of the valve including the area occupied by the opened discs or leaflets, struts, and other mechanisms of the valve
• Calculation of the circular area, the radius of which is half of the IOD. 
• It is measured in square centimetres

Clear Orifice Area (COA)

• Obtained by subtracting the area of opening  components of the valve from GOA
• Its value is seldom declared.  

Effective Orifice Area (EOA)

• The most important parameter of both mechanical valves and bioprostheses
• It is that portion of the valve orifice area through which the blood really flows 
• It is usually one quarter or one third smaller than GOA
• It is measured in square centimetres

Indexed Effective Orifice Area (IEOA)

• Effective Orifice Area in related to 1 square meter of the body surface area
• Need to implant a valve large enough to avoid haemodynamically significant Patient Prosthesis Mismatch (PPM)
• In Aortic position: IEOA should be greater than 0.85cm²/m²
• In Mitral position: IEOA should be greater than 1.2cm²/m²
• Moderate PPM: IEOA 0.85 to 0.65cm²/m²
• Severe PPM: 

                  Aortic Position: IEOA less than 0.65cm²/m²
                  Mitral position: IEOA less than 0.9cm²/m²

• Values declared by the  manufacturer used to look more optimistic (in vitro values) than post-implantation echocardiography values calculated on the basis of continuity equation (in vivo values)

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