Cardiac Path Online
Pathology of Prosthetic and Bioprosthetic Heart Valves
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.
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). Mention whether it is 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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