The aorta (main artery) branches off from the left ventricle and carries oxygen-rich blood into the systemic circulation. The aortic valve, one of four heart valves, is a valve that sits directly at the base of the aorta.
It allows the oxygen-rich blood to pass through and then closes the aorta until the next heartbeat so that the blood does not flow back into the ventricle.
If the aortic valve does not close the aorta tightly, this is a case of aortic valve insufficiency. In this case, blood can flow back.
On the other hand, it is also possible that the aortic valve does not open wide enough and therefore too little blood enters the systemic circulation. This is known as aortic valve stenosis (narrowing).
The indication for an aortic valve replacement is given if the function of the aortic valve needs to be restored so that the blood flow remains guaranteed.
Aortic valve replacement is particularly necessary if the natural aortic valve can no longer be reconstructed. The main purpose of aortic valve replacement is to prevent chronic heart failure.
Indications for aortic valve replacement include
- Aortic insufficiency (inadequate closure of the aortic valve)
- Aortic stenosis (narrowed outflow tract of the left ventricle)
- Mitral insufficiency ("leaky" mitral valve)
- Mitral stenosis (narrowing of the mitral valve opening)
The first mechanical prosthesis in the history of cardiology was implanted in 1952. The American surgeon Charles Anthony Hufnagel developed an artificial heart valve, which he implanted in the descending aorta of a 30-year-old woman with aortic valve insufficiency.
Mechanical heart valves consist of a metal body encased in a polyester cuff. This cuff is used to stitch the valve to the human heart tissue.
Mechanical valves are characterized by the so-called "prosthetic click", a metallic clicking sound that occurs when the heart valve closes. The clarity of this sound indicates whether the aortic valve replacement is in good condition or whether deposits have already formed.
Advantages and disadvantages of mechanical heart valves
The advantage of mechanical heart valves over bioprostheses is their long service life. Tests have shown a (theoretical) lifespan of 100 to 300 years for mechanical valves. This is why they are often implanted in young patients.
However, metal prostheses also have disadvantages: The metal surface has a clot-activating effect, which leads to an increased risk of embolism and thrombosis.
Patients with a mechanical heart valve must therefore take anticoagulants for the rest of their lives. These are anticoagulant drugs that are used prophylactically to prevent blood clotting. Patients are usually prescribed the anticoagulant Marcumar. This must be taken daily and the coagulation value, the so-called INR (International Normalized Ratio), must be checked every two weeks.
Types of mechanical heart valve prostheses
A distinction is made between the following types of mechanical prosthesis:
- Double leaflet prosthesis (e.g. St. Jude Medical): Valve prosthesis consisting of two leaflets
- tilting disk prosthesis (e.g. Medtronic-Hall, Björk-Shiley): single-wing valve model
- Ball prosthesis (e.g. Starr-Edwards or Smeloff-Cutter): first used in 1952, no longer used today.
- Lifting disk prosthesis (e.g. Kay-Shiley): This model is also no longer implanted today.
1. rigid Edwards heart valve; 2. rigid Edwards heart valve; 3. Smeloff-Cutter heart valve; by Dr. Mirko Junge - Own work (Own photo), CC BY 3.0, Link
The biological alternative to metal prostheses is an aortic valve replacement made from human or animal tissue. Biological valves are less durable than mechanical valves, lasting around 10 to 20 years. After that, the heart has to be operated on again. Biological heart valves are divided into xenogeneic heart valves, homologous heart valves and autologous heart valves.
Xenogenic heart valves
These biological heart valves (also known as xenograft) are obtained from the heart tissue of pigs or cattle. Xenograft means that the donor of the organ comes from a different biological species than the recipient.
This aortic valve replacement is attached to a flexible scaffold construction surrounded by a polyester ring. However, there are also variants without a scaffold; these models are only reinforced with Dacron, a synthetic material made from continuous polyester threads.
The bioprostheses with the longest service life are scaffold prostheses made from pig hearts (such as the Carpentier-Edwards prostheses or the Hancock prostheses). Only temporary anticoagulation is required for xenogeneic heart valves.
Homologous heart valves
These valves are also referred to as homograft, which means that the donor of the organ comes from the same species as the recipient. Homologous heart valves are therefore obtained from the heart tissue of deceased human donors.
The patient does not have to take anticoagulants after the operation.
The disadvantage of this replacement is the increased risk of degeneration and the limited availability of this type of valve.
Autologous heart valves
Tissue engineering is used to cultivate the patient's own cells in order to produce so-called autografts. These are transplants in which the cells are taken from another part of the body. Autologous heart valves are therefore produced by cultivating the patient's own cells in a bioreactor.
There are two surgical methods in heart surgery: open surgical aortic valve replacement and the minimally invasive method.
In the first method, surgery is performed on the open thorax (chest) using a heart-lung machine (under general anesthesia). In the minimally invasive method, the aortic valve replacement is inserted using a catheter. This procedure is only possible with a bioprosthesis.
If there are no complications, patients can leave the clinic after two to three weeks.
As with any operation, risks can occur, depending mainly on the severity of the disease and the patient's constitution:
- Cardiac arrhythmia
- blood clot formation
- less frequently: insufficient function of the heart valve
- Wound infections
- Hoarseness/throat pain (due to the breathing tube)
- Pericarditis
- Infection of the inner lining of the heart
- Blood clotting disorders
