Pros and Cons to Artificial Heart Valves
| Cons |
Pros |
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Patients need to be on a heart lung machine and the longer they are on the machine the worse it is to their health More likely than mechanical valves to structurally fail due to late calcification Structural failure due to tears and perforations Best in elderly patients ages 65 and greater due to less stress on prostheses and less risk of calcification.
|
No anticoagulation therapy needed Only a small chance of rejection Improved hemodynamics No stent needed but stented valves are easier to implant Freedom from anticoagulation hemorrhage Low rate of serious thromboembolism Better hemodynamic characteristics and less hemolysis |
Biggest problems facing porcine valves is thromboembolism and in young patients, tissue valves implants will need to be replaced periodically.
Fig 1. - Comparison of mechanical valves and biological valves implanted from the years of 1975 to 1994.
Table 1 - Results from a 17 year study of the Carpentier-Edwards. Total deaths related to increased heart problems/problems with implant.
Design Criteria
For a replacement heart valve to be a success, either tissue or mechanical, there are some important criteria that have to be meet. When dealing with any device that comes in contact with the circulatory system there are some rules. The blood is very sensitive and can easily become damaged. A replacement valve should do no damage to the blood cells. Additionally, the material a valve is made of can cause clotting. Blood easily sticks to even the smoothest metals and polymers. The hinges of a mechanical valve can gather blood very quickly.
A successful heart valve replacement will allow the blood to flow uninterrupted and very close to normal hemodynamics. Tissue valves tend to have much better hemodynamics than mechanical valves. Because of the way older mechanical valves were designed the ball or disc got in the way of the flow of blood and caused the artery to bulge around the valve to allow the blood to flow. The valve must also be able to be sewn into the heart easily and stay there. It is important to know the size of the valve needed so it fits into the space perfectly. If the valve is too large it can be painful and if the valve is too small it may slip and move from where it was placed. The heart is a pump and if the pump is working properly any active device could mess up with the cycle of contractions. Any valve replacements must be passive and open and close with the flow of blood produced by the heart.
Critical to the success of the valve is to not have the body produce an immune response. This is a general problem with tissue valves. To correct this animal valves are preserved and the antigens removed; there is usually no immune response. The same is done with homograft valves. Autograph valves should not produce an immune response since they are made from the tissue of the very same patient. Mechanical valves are made from inert metals and polymers that should not react with the body’s environment or cause an immune response. But patients who have mechanical valve implants will have to take anticoagulation medicine for the rest of their life.