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Prosthetic associated problems are unusual in the early post-operative
period but late complications do occur and can cause death.
Mechanical
prostheses (caged-ball, caged disk, tilting disc designs and tissue
derived valves (bioprosthesis) are the two types most commonly used in
use. The major tissue valves today are xenografts fabricated
from porcine aortic valve or pericardium preserved in a dilute
glutaraldehyde solution.
Homografts
from human cadavers are also being used.
Causes of
failure include thromboembolic, infection, tissue overgrowth, leak or
partial dihescence and durability problems caused by material
degeneration.
The advantage
of tissue valves is their non-thrombogenicity.
Degenerative
changes with calcification are the chief cause of bioprosthesis
failure which causes cuspal rigidity or tearing usually 3-4 years
after valve replacement.
Cuspal tears
and perforation can occur in the absence of calcification and is
probably related to connective tissue structural failure.
Though the
base of the heart is composed of dense fibrous tissue it does contain
small arteries and veins and the many sutures used to anchor the
valves can cause bleeding. This may track to the epicardial surface
giving the impression of a blister.
The mortality
for mitral valve replacement is greater than for aortic procedure.
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Major
Complications of Valve Replacement:
Infective
endocarditis ; Perivalvular leaks ; Thrombosis ; Pannus
formation ; Structural failure. |
An approach to
examination of Prosthetic Valves:
1. Identify
the type of prosthesis. Measure the external diameter of the outside
sewing ring The type of valve is included in the diagnosis.
2. Describe
any tissue overgrowth of the sewing ring.
3. For
mechanical valves ,also describe any asymmetry, notches, cracks, or
any of the components.
4. For tissue
valves, describe any tears or perforations of the cusps and/or any
impairment of cusp motion.
5. Describe
any tissue overgrowths, vegetations including colour, size (surface or
valve, sewing ring), consistency ( firm, friable), ?destructive
to underlying material.
6. Describe
any calcific deposists and their location. Calcification will be
graded on a scale from 0-4 using a specimen radiograph.
7. Photograph
all valves. Radiograph all tissue valves.
In most cases
it is appropriate to submit a portion of bioprosthetic valve cusps for
histologic examination. Tissue on the sewing ring adjacent to any
valve prosthesis is always submitted. In cases of suspected
endocarditis, Gram and fungal (methenamine silver) stains are ordered
in advance.
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