Our heart is made of four chambers, two on the right & two on the left. The upper chamber on each side (right or left atrium which collects impure & pure blood respectively.) is the collecting chamber & the lower chamber (right or left ventricle which pumps impure blood to the lungs for purification & pure blood to the whole body.) is the pumping chamber. The blood needs to flow in a particular direction unobstructed & without leaking back. To achieve this four valves in the human heart. On the right side, the tricuspid valve is situated between the collecting & pumping chambers whereas on the left side the same job is done by the mitral valve. The remaining two valves are positioned at the outlet of each pumping chamber. On the right side, the valve between the pumping chamber & the main artery carrying the impure blood to the lungs is called the pulmonic valve. Similarly, on the left side, the valve between the pumping chamber & the main artery carrying the pure blood to the entire body is called the aortic valve.
In India, the commonest cause of damage to these valves is rheumatic fever. Other causes include congenital valve deformities & degenerative valve disease. The left-sided valves viz. mitral & aortic are much more commonly affected than the right-sided valves.
The treatment options include valve repair & valve replacement. Valve repair can be performed in any age group but needs to be done early in the disease process before the valve is severely damaged. This always is the best option because it preserves the native valve. However, this is not frequently possible because it requires special surgical expertise as well as good intraoperative facilities like transesophageal echocardiography. The repair needs to be durable in the long term otherwise it necessitates a repeat operation to replace the valve which not only involves the additional cost but also a much higher risk than the first operation.
When valve replacement is recommended, the choice of a valve depends on multiple important factors which need to be discussed in details with the patient. Unfortunately, it is not done. There are two types of valve replacement devices, mechanical & bioprosthetic.
Types of Valve’s
There are many kinds of mechanical valves available in the market. Which particular valve to use depends on the Surgeons comfort & track record of the valve. The cost of the valve may be a consideration in some cases. Mechanical valves are made of a special kind of metal called pyrolitic carbon. It is the same metal that is used to make the exterior of spacecraft. There are two types of mechanical valves, single leaflet & bileaflet. All the valves are made in the western countries except Chitra mechanical valve which was invented by Dr. S.Valiathan from the SriChitra Tirunal Institute of medical sciences at Thiruvananthapuram.
Any foreign object in the bloodstream induces clot formation. Likewise, a mechanical valve in the heart can get obstructed by clot formation. Therefore it is necessary to anticoagulate the patient lifelong with the help pf medicines like warfarin or acitrom. The dose of the anticoagulants depends on the position of the implant of the valve & associated medical conditions. Monitoring the level of anticoagulation is extremely important as it depends on multiple factors. Anticoagulation is affected by the drug dose, type of drug, drug interactions with other medicines taken by the patient, daily diet, exercise routine etc. Under or over-anticoagulation can be lethal. Underanticoagulation can block the valve & over anticoagulation can cause spontaneous bleeding anywhere in the body. Anticoagulation testing is available in most pathological laboratories in major cities.
Laboratory to laboratory variation exists; therefore it is important to get blood tested from the same reliable laboratory every time. Frequent testing is advisable to ensure adequate anticoagulation. Mechanical valves last a lifetime. Therefore if the anticoagulation is properly managed the patient should not need a second operation to replace that valve. However, there are disadvantages to be on blood thinners. Trivial injuries will bleed a lot more than normal people. Emergency operations are dangerous from the bleeding point of view & need elaborate preoperative preparation. Anticoagulation is contraindicated for pregnant women or for those who wish to conceive because it can cause intrauterine bleeding, cerebral hemorrhage in the fetus, causing a stillbirth or life-threatening bleeding from the uterus at the time of delivery. The associated medical condition makes also contraindicate anticoagulation like patients with intracranial bleed, peptic ulcer etc. Therefore detail medical history prior to surgery is of vital importance.
This is the other alternative. These can be human or animal. Cryopreserved valves called homografts used mainly in the aortic positions because mitral homografts have not worked well in long-term. Aortic homografts are harvested from cadavers in a sterile manner & preserved in liquid nitrogen at -1 to 3 degrees centigrade. The process of harvesting & cryopreservation is elaborate & needs a homograft bank facility which is not easily available in our country. Therefore they are costly & in short supply. Also an operation with the homograft is a complex & technically difficult which need special training. Redo operation with the homograft is also much more complex than a redo operation with the animal bioprosthetic valve.
Animal bioprosthetic valves are either made from a pig’s aortic valve or cow’s pericardium. In spite advanced technologies to prevent degeneration of these animal valves, they do not last a lifetime. Younger the patient lesser is the durability of these valves. Therefore the patient will certainly need a second operation to replace these degenerated valves. Depending on the age of the patient these valves will last anywhere from five years to fifteen years. However, the big advantage of bioprosthetic valves is that they do not need anticoagulation & the patient is free from all the risks of anticoagulation-related complications. Bioprosthetic valves are costlier than mechanical valves by 20-25%. Unfortunately, with the current state of medical technology & medical research, there is no artificial heart valve that will last a patient’s lifetime & also will not need anticoagulation.
→ Special precautions
Any patient with an artificial heart valve must be very careful in preventing any infection in the body. Therefore fever should not be taken lightly & must be treated very aggressively. Before any operative procedure e.g. dental work antibiotic prophylaxis is mandatory to cover the entire operative period. If these precautions are not followed strictly the artificial valve can easily get infected. An infected artificial valve will almost always require re replacement.
There is no the difference in the surgical risk or the surgical skills required for mechanical or animal heart valves. Therefore choice of the type of valve has to be made by the patient only after understanding all the above the factors.