In cardiac surgery, aortic valve replacement refers to the implantation of an artificial heart valve. A so-called endoprosthesis is used for the aortic valve. This prosthesis is a medical implant consisting largely of metal, and there are various types available. A biological implant may also be used. Whether a mechanical or biological valve is appropriate depends on the patient’s individual circumstances.
Further information on aortic valve replacement can be found below.
What is the aortic valve?
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 located directly at the base of the aorta.
It allows the oxygen-rich blood to pass through and then closes off the aorta until the next heartbeat. This prevents blood from flowing back into the ventricle.
If the aortic valve does not seal the aorta tightly, this is called aortic valve insufficiency. In this case, blood can flow backward.
It is also possible that the aortic valve does not open wide enough, causing too little blood to enter the systemic circulation. In this case, doctors refer to aortic valve stenosis (narrowing).
Who needs an aortic valve replacement?
Aortic valve replacement is indicated when restoration of the aortic valve’s function is necessary to ensure proper blood flow.
Aortic valve replacement is particularly necessary when the natural aortic valve is no longer functional or cannot be reconstructed. The primary goal of aortic valve replacement is to prevent chronic heart failure.
Indications for aortic valve replacement include, for example:
- Aortic regurgitation (inadequate closure of the aortic valve)
- Aortic stenosis (narrowing of the outflow tract of the left ventricle)
- Mitral regurgitation (“leaky” mitral valve)
- Mitral stenosis (narrowing of the mitral valve opening)
Aortic valve replacement with mechanical heart valves
American surgeon Charles Anthony Hufnagel developed an artificial heart valve in 1952. He implanted it into the descending aorta of a 30-year-old woman with aortic valve insufficiency. This was the first heart valve in the history of cardiology.
Mechanical heart valves consist of a metal frame encased in a polyester sleeve. Doctors use this sleeve to suture the valve to the human heart tissue.
A characteristic feature of mechanical valves is the so-called “prosthetic click,” a metallic clicking sound produced 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 bioprosthetics lies in their long durability. Tests have shown that mechanical valves have a (theoretical) lifespan of 100 to 300 years. For this reason, they are often implanted in young patients.
However, metal prostheses also have disadvantages: The metal surface promotes blood clotting, 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 medications used prophylactically to prevent blood clotting.
Patients are typically prescribed the anticoagulant Marcumar. They must take this medication daily. They must have their coagulation level—known as the INR (International Normalized Ratio)—checked every two weeks.
Types of Mechanical Heart Valve Prostheses
The following types of mechanical prostheses can be distinguished:
- Double-leaflet prosthesis (e.g., St. Jude Medical): a valve prosthesis consisting of two leaflets
- Tilting-disc prosthesis (e.g., Medtronic-Hall, Björk-Shiley): a single-leaflet valve model
- Ball valve prosthesis (e.g., Starr-Edwards or Smeloff-Cutter): First implanted in 1952, it is no longer used today.
- Lift-disc prosthesis (e.g., Kay-Shiley): This model is also no longer implanted today.
1. Starr-Edwards heart valve; 2. Starr-Edwards heart valve; 3. Smeloff-Cutter heart valve; by Dr. Mirko Junge - Own work (Own photo), CC BY 3.0, Link
Aortic valve replacement with biological heart valves
The biological alternative to metal prostheses is aortic valve replacement using human or animal tissue. The lifespan of biological valves is shorter than that of mechanical valves; it is approximately 10 to 20 years.
After that, another surgery is required.
Medical professionals classify biological heart valves as follows:
- Xenogeneic heart valves
- Homologous heart valves and
- Autologous heart valves
- Xenogeneic heart valves
These biological heart valves (also known as xenografts) are derived from the heart tissue of pigs or cattle. Xenograft means that the organ donor belongs to a different biological species than the recipient.
Doctors attach these aortic valve replacements to a flexible scaffold structure surrounded by a polyester ring. However, there are also scaffold-free variants. These models are reinforced only with Dacron, a synthetic material made of continuous polyester filaments.
The bioprostheses with the longest lifespan are scaffolded prostheses derived from pig hearts (such as the Carpentier-Edwards prostheses or the Hancock prostheses). With xenogeneic heart valves, only temporary anticoagulation is necessary.
Homologous heart valves
These valves are also called homografts, which means that the organ donor is of the same species as the recipient.
Homologous heart valves are made from the heart tissue of deceased human donors.
After surgery, the patient does not need to take anticoagulants.
The disadvantages of this type of replacement are the increased risk of degeneration and the limited availability of the valve.
Autologous Heart Valves
Using tissue engineering, the patient’s own cells are cultivated to produce what are known as autografts.
Doctors harvest cells from other parts of the body for this purpose.
Autologous heart valves are thus created by culturing the body’s own cells in a bioreactor.
The Surgery and Its Risks
There are two surgical methods in cardiac surgery:
- open-heart aortic valve replacement and
- the minimally invasive method
In the first procedure, surgery is performed on the open thorax (chest) using a heart-lung machine (under general anesthesia).
In the minimally invasive method, doctors implant the aortic valve replacement using a catheter. This procedure is only possible with a bioprosthesis.
If no complications arise, patients can be discharged from the hospital after two to three weeks.
As with any surgery, risks may arise, depending on the severity of the disease and the patient’s physical condition:
- Heart rhythm disturbances
- Blood clot formation
- Less commonly: inadequate heart valve function
- Wound infections
- Hoarseness/sore throat (due to the breathing tube)
- Pericarditis
- Endocarditis
- Blood clotting disorders
