VALVE PROSTHESIS
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
- 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
- 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
TAD Tissue Annulus Diameter
ESRD External Sewing Ring Diameter
Implantation PositionS
Intra-annular Position
Intra-supra-annular Position:
Supra-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
PROSTHESIS ORIFICE AREAS
GOA, COA, and EOA of
Left Column Bileaflet valves
Centre column: Tilting mono-discs
Right column:Bioprostheses
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
- Obtained by subtracting the area of opening components of the valve from GOA
- Its value is seldom declared.
- 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
- 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:
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)