VALVE REPLACEMENT: Which valve?
There is always confusion in the minds of people as to which valve we should use for valve replacement. Broadly, there are two types of prosthesis (valve implants) currently in use, namely mechanical valve and tissue valve (bioprosthesis).
One type is made of artificial material and usually is a rigid valve. The material used is usually pyrolytic carbon or high density polyethylene. The latter is used primarily in the Chitra TTK valve that is manufactured in India. There does not seem to be any long term difference in the type of valve used. Mechanical prosthesis will last a lifetime usually if one takes good care of them. To prevent these valves from clotting, we have to use some tablets that reduce the clotting tendency of the blood. These tablets are powerful and so they are also dangerous. We have to monitor the effect of these tablets or else if the effect exceeds what is required, patient may suffer bleeding tendencies. On the other hand, if the effect is less than optimal, clot formation may occur on the valve or the valve can get stuck. The test done for monitoring the vitamin K antagonists is the Prothrombin time test and it is controlled by quality control. We therefore get an International Normalisation Ratio (INR) after standardisation of the particular laboratory. This INR should be maintained at 1.5<———> 3.5 range for aortic valve replacement and between 2.0<———>4.0 for the mitral valve. Other tablets that are used for deep vein thrombosis such as Dabigatran have not been recommended for the valve replacement management. We usually ask the patient to consume less of green leafy vegetables as it contains lot of vitamin K. The INR has to be done regularly so that it is prevented from going up too high or fall too low.
Besides the problem of anti coagulation, we find certain peculiar problems associated with mechanical valves. One of them is the chance of getting infected. This leads to infective endocarditis, which is a very dangerous condition. It has a lot of local effects such as formation of intra-cardiac abscesses as well as systemic effects of infection such as fever or embolisation to the brain or other organs. Another complication may occur after many years and that is the formation of “pannus”. This is formation of thickened tissue that grows around the valve ring and eventually encroaches on the valve leading to impairment of its function. In such situations, you may need a re-replacement of the valve.
The other type of valves that is available for use is the tissue valves. This may be made of porcine or bovine material. Valves of porcine material may not be accepted by people with certain religious sentiments, so that is to be explained to the patient and relatives before surgery. Even though the technology for making this valves has improved in the last few years, we do find that some of the valves degenerate after some years and that would lead to recurrent leak or stenosis of the valves. Tissue valves or bioprosthesis are more resistant to infection than mechanical valves so they are preferred in patients with infective endocarditis. Also the valves do not need anticoagulant for life as in the case of mechanical valves. We usually give anticoagulants for about 2-3 months and prescribe it further only if the patient has rhythm disturbances (atrial fibrillation). It Is advised that in those female patients of childbearing age, we should prefer tissue valves to prevent the potential harmful effects of the medicines on the pregnancy. However, in our practice, we have found that some patients had early degeneration of the tissue valves and had to have re-replacement. On the other hand, some of the patients who underwent valve replacement with mechanical valves underwent pregnancy and childbirth without any problem. Of course, they and their obstetricians did take proper care of the anticoagulants as explained in our page on guidelines (. ) Hence we have stopped recommending tissue valves and are explaining all this facts to the patient and relatives before they can make the decision on which type of valve to be used.
Mechanical valves
- Life long anticoagulants
- Can get infected
- Can last life long if proper care taken
Tissue valves
- Only short term anticoagulants
- Can degenerate in time
- Useful in infective endocarditis
- Can undergo valve in valve implantation
Trans-aortic valve re-implantation
This is a relatively new technology in which we place a valve within the natural aortic valve or in a previous bioprosthetic valve over a wire. We can do this by passing the wire and system through the femoral artery in the thigh or from the arm arteries, the neck vessels, directly into the aorta or from the apex of the arm. The main advantage of this is that we do not have to use cardiopulmonary bypass in most of the cases. It is therefore indicated in patients in whom the standard surgery would be of risk such as elderly patients. There is some incidence of heart block (conduction defect) in some patients however the benefits definitely outweigh the potential complications.
Suture less valve
One can use this valve in patients in whom we have a highly brittle calcification of the aortic valve or in whom the annulus is very friable. The valve needs cardiopulmonary bypass and opening of the heart and some time to be prepared after sizing the valve annulus. There is also some incidence of heart block in some cases.
