Valve prostheses. They are industrially manufactured or prepared heart valves , which are used in patients with valve insufficiency or valve stenosis .
When heart valves become sick, two types of injuries occur: narrowing or melting of the valve (stenosis), which makes it difficult for the valve to open and the passage of blood , and insufficiencies or defective valve closure that causes blood to flow in wrong address. Some injuries cause early suffocation and fatigue ( mitral stenosis ) but others only give symptoms in very advanced stages of the disease ( aortic stenosis ).
The surgical repair of a valve implies its reconstruction, so that it works correctly or its replacement by a valve prosthesis. Surgery is recommended in people who have significant symptoms that prevent a reasonable life for their age or in symptomatic patients whose life is short-term due to the nature of the injury.
During surgery to repair or replace a valve, the sternum is divided , the heart is stopped, and blood is diverted to an extracorporeal circulation machine. Because the heart or aorta needs to be opened , cardiac valve surgery is an open-heart procedure. Valve replacement involves exchanging an existing valve for a biological or mechanical prosthesis.
Summary
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- 1 In which cases is a valve replaced
- 2 Types of prosthetics
- 1 Mechanics
- 2 Biological
- 2.1 Types of biological prostheses
- 3 What problems can prosthetic valves present?
- 4 Percutaneous aortic prosthesis implant
- 5 Risks of treatment
- 6 Valve surgery
- 7 Sources
In which cases a valve is replaced
They are replaced in congenital heart diseases that produce valve deformities from fetal life; in injuries caused by rheumatic fever (generally infantile and as a consequence of poorly healed angina), they cause mitral and aortic disease (stenosis and / or insufficiency) and in degenerative injuries, which appear in the elderly, due to wear and calcification. The best known is calcified aortic stenosis in the elderly, although mitral valve regurgitation is also not uncommon.
Types of prosthetics
Mechanical
They are made of materials such as plastic , metal and the latest models consist of a small cylinder of pyrolytic carbon. The pyrolytic carbon is graphite bombarded with atoms of carbon at high temperatures, a material almost as hard as diamond . It is very little thrombogenic (not very likely to produce clots or strokes ) and begins to show wear after an equivalent of 80 years of operation. However, over time, these prostheses become clogged, so patients need to take anticoagulants daily and indefinitely.oral. In general they have a useful life of 20 to 30 years.
Biological
Made of animal or human tissue. They are recommended in patients who do not want to take anticoagulants or want to continue with risk sports; in those with additional medical problems such as a stomach ulcer, pre-existing bleeding disorders or being very old; and in women who wish to pregnant (who should not take blood thinners due to the risk of fetal malformations); since they have very little tendency to form embolisms or thrombosis even without coagulants.
Types of biological prostheses
There are currently three types of biological prostheses: ring-mounted pig aortic valve grafts ; constructed of the membrane covering the heart ( pericardium of cow ) and also mounted a ring; human cadaver aortic valve grafts (homograft), which are sewn directly without a ring. The latter are the least used due to the difficulties derived from obtaining them.
The main drawback of biological prostheses is a duration limited to 12-15 years. After that time they have to be replaced as they calcify or tear. For this reason they are only used in three out of ten cases.
What problems can prosthetic valves present?
Problems depend on the type and location of the valve. In general, mechanical valves cause more problems than biological ones:
- Clot formation – can break and cause an obstruction (arrest) to blood flow somewhere in the body; They can also cause valve blockages.
- Problems derived from anticoagulation (prevents formation of clots): it can promote heavy bleeding.
- The valves can become infected ( endocarditis): formation of small vegetations on the valve that can break or block the valve.
- They may leak or block due to the presence of scar tissue.
- It can damage red blood cells( blood cells) causing hemolytic anemia (breakdown of red blood cells).
Percutaneous implant of aortic prostheses
Emerging technology has developed bioprostheses that can be implanted percutaneously (puncture of the femoral artery , leg, catheter-like , without surgery) in adult patients with degenerative aortic stenosis who are at high risk for surgery or not. want to have surgery.
The French Alain Cribier, developed in 2002 the method of implanting an artificial prosthesis to implant with cardiac surgery, began the first percutaneous implants of aortic prostheses in humans. Since then, this treatment has been evolving very rapidly. Two percutaneously implanted aortic prostheses are currently being used: one of nitinol (an alloy of cobalt and titanium ) and the other of steel .
The percutaneous implantation of aortic valves is a very attractive procedure for patients, since it is not necessary to open the patient’s chest, in many cases it does not have general anesthesia (it is carried out with sedation) and allows for early discharge from the hospital.
Treatment risks
Wearers of cardiac prostheses should then continue under the supervision of a cardiologist, to control anticoagulation, avoid or treat infections that may settle in the prosthesis, and to follow the evolution of the prosthesis and the heart.
The percutaneous implant has the drawback of the difficulty of implantation, so it is necessary to select well the patients who are offered the procedure.
Valve surgery
The approach in surgery is the usual one (see section: During Cardiac Surgery). A median sternotomy is performed, which is the longitudinal opening of the sternum, the bone in the center of the chest. Subsequently, the pericardium (a kind of bag that surrounds the heart) is opened and, in this way, the heart is accessed. The next step is to connect the patient to the extracorporeal circulation, making it possible at that time to stop the heart.
In the case of aortic valve disease , an incision is made in the aortic artery, which allows access to the valve. The three veils that form the aortic valve are resected and the orifices where the coronary arteries originate (ostia coronarios) are located. It is important to identify them so as not to cover them later with the prosthesis. The prosthesis (generally biological) is then implanted by suturing it to the aortic annulus with permanent stitches. Following this, the incision in the ascending aorta is closed and the function of the heart is restarted.
In the case of mitral valve disease , it is replaced by a prosthesis when it cannot be repaired (most cases of mitral stenosis or double mitral injury, as well as valve insufficiencies that cannot be repaired). Once the heart has stopped, an incision is made in the left atrium (atriotomy) to access the valve, and the mitral valve is removed. The implant of the prosthesis (usually mechanical), as in the aortic position, is performed with non-absorbable points. Once the prosthesis is sutured, the atriotomy is closed and the function of the heart is restarted.
Once the valve has been replaced, it is verified that the heart beats properly and is disconnected from the extracorporeal circulation. Subsequently, adequate hemostasis is performed (check and cancel all possible bleeding points), the drainage tubes are inserted and an external pacemaker cable is implanted. This cable can be connected to an external pacemaker generator if necessary; for example, if the heart beats too slowly during the postoperative period. Lastly, it is performed in closure of the sternum, and suturing of the subcutaneous cell tissue and skin. Finally, the patient is transferred to the Intensive Care Unit. After the operation, the patient usually goes home a week if there have been no complications.
All carriers of a heart valve prosthesis should take an antibiotic prior to those situations that facilitate the passage of bacteria into the blood, such as dental manipulations, genitourinary, colonoscopies, etc. This is essential to prevent endocarditis infectious
