Valve replacement:

Old replacements:

- Caged ball valve - there were a variety of problems associated with theses valves:4

- Thrombus formation of the prosthetic valve was too common.

Newer valves:

1) St. Jude mechanical valve- It is a double flap closure valve and does not always have part of the prosthesis (the occluder) in the way of blood flow as in the caged ball valve does. This gives a relatively unimpeded laminar flow of blood as compared to the other.

2) The porcine valve prosthesis ( pig valve) -

The pig aortic valve's leaflets are actually sewn into a cloth covered material called a stent . (This is all factory produced.) The valve is then sewn into the heart of a patient. The valve is completely self supporting - mimicking the original anatomy of the aortic valve.

The great thing about the pig valve is that its self supporting valve can be used for any valve replacement (mitral, tricuspid, and also rarely in the pulmonic valve as well) in the heart, not just the aortic. Of course, the valve has to be placed in the right direction for all of these different replacements, and the appropriate size must be used as well.

Bovine valves have also began to be manufactured now as well.

These newer valves are also prone to problems- but not as great as the caged ball model.

- These valves could also develop thrombosis

- The valves are subjected to the same wear and tare as the native aortic valve experienced and therefore have a tendency to deteriorate - they may calcify and become stiff. They can break apart and become insufficient.

In general problems related to prosthesis:

- prosthesis endocarditis

- prosthesis dehiscence

- prosthesis dysfunction

a. obstruction

- thromboembolus

- hemorrhage

Question -What is the average life span of these newer valves?

The pig valve has an anticipated failure of 1/3 after about 10 years, so that this would not be the choice valvular replacement for a child or young adult. The St. Jude's valve could last a lifetime if the patient is also kept on anticoagulants. The trade off lies in the idea that with the pig valve one might not have to be maintained on a lifetime anticoagulant regime.

How is it that humans accept pig or cow tissue without rejection?

In general you can not. Gradual deterioration of the porcine valve does not relate to immunologic factors . Curiously, these substances are not antigenic, partly because of the way they are treated or manufactured. The pig aortic valve is not implanted as a living metabolically active tissue. The pig tissue is treated with glutaraldehyde which is essentially a "tanning process". So, basically you are inserting a piece of tanned shoe leather into a patient. Due to this process the foreign tissue is rendered non - antigenic. It is believed that the treatment somehow binds up haptens that would have been immumologic determinants. Therefore, there is no antibody reaction to the tissue.

Gortex (?) was also used in an attempt to construct prosthetic heart valves - this was not a success.

Question - Is there any predisposition to survival of heart valves in certain individuals?

Answer - In general no. In the past, some young children seem to have a predisposition to valve calcification. The age cut off for what is considered young in the literature is <>

Question - Is there a problem with valve replacement in people with tissue diseases? ( as in Lupus, rheumatoid arthritis etc.)

Answer- In general no.

Category: Pathology Notes