Heart valve replacement

from Wikipedia, the free encyclopedia

A heart valve replacement or artificial heart valve is an artificially introduced replacement for a natural heart valve . A distinction is made according to the position ( the aortic valve , mitral valve , pulmonary valve or tricuspid valve ) according to the type ( mechanical and biological heart valves) and after the implantation method ( open surgery or minimally invasive ) of the valve replacement.

Heart valve reconstruction is the alternative method, depending on the indication .

history

Valve used by Hufnagel
1. Rigid Edwards heart valve
2. Rigid Edwards heart valve
3. Smeloff-Cutter heart valve

On September 11, 1952, Charles A. Hufnagel of Georgetown University inserted a heart valve he had developed into the descending aorta ( aorta ) of a patient with aortic valve insufficiency. The artificial valve was thus clearly removed from the natural aortic valve, which is located at the aortic base, but nevertheless improved the blood flow (hemodynamics). The technique had previously been tested on dogs.

The first artificial heart valve in the form of a ball prosthesis was by the two Americans in 1961 Albert Starr and Lowell Edwards implanted .

In 2010, 30,492 heart valve replacement operations were performed in Germany. Aortic valve replacement accounted for the largest share of this with 26,208 (86.0%). Reconstruction was often possible in mitral valve vitia (7,728 interventions), mitral valve replacement was performed 4,146 times (13.6%). The tricuspid valve replacement played only a minor role with 138 interventions (0.4%).

indication

The indication for surgery depends on clinical symptoms and objective criteria. In addition to relieving symptoms, the main aim is to prevent acute or chronic heart failure . The stroke volume and thus the cardiac output should be increased. The following list gives a simplified overview of the most common operations. That are not mentioned here Trikuspidalklappenstenose that tricuspid regurgitation , the pulmonary valve , the pulmonary valve and the combined heart defects.

Aortic stenosis

  • severe aortic stenosis and symptoms
  • Severe aortic valve stenosis without symptoms with reduced pump function ( EF <50%) or pathological stress test or rapid progression

Aortic regurgitation

  • severe aortic regurgitation and symptoms
  • Severe aortic valve insufficiency without symptoms with reduced pump function ( EF <50%) or end-systolic diameter of the left ventricle> 50 mm

Mitral valve stenosis

  • Significant symptoms and valve opening area <1.5 cm² and valvuloplasty not possible
  • low symptoms and valve opening area <1.0 cm² and valvuloplasty not possible

Mitral valve regurgitation

Open surgical technique

After the indication for open surgical aortic valve replacement, examinations are carried out to assess the risk of surgery and anesthesia. These include e.g. B. a pulmonary function test and a cardiac catheter examination . If coronary artery disease is diagnosed in the latter , the creation of coronary artery bypasses, which can be done in one session with the valve replacement , is usually recommended.

Operational sequence

Doctor's letter after aortic valve replacement

The operation is performed under general anesthesia using the heart-lung machine . The chest is opened by sawing open the breastbone (median sternotomy ). After opening the pericardium and exposing the heart, the heart-lung machine is connected. It enables the blood to be supplied to the body while switching off the heart by clamping off the large vessels. The heart is brought to a standstill by means of a cardiopulmonary solution . Now the affected heart valve is exposed. In the case of aortic valve replacement, this is done via the aorta; access to the mitral valve is via the left atrium. If necessary, the affected heart valve is first decalcified and then removed. To do this, the valve leaflets are cut out of the valve ring. The aim is to create space for the largest possible valve prosthesis. To fix the prosthesis, holding threads with felt reinforcement are placed. The artificial heart valve is guided and fixed in the correct position via this. With aortic valve replacement, the type of fixation differs depending on the prosthesis used. Biological valves without a mechanical framework are used either while preserving their own coronary vessels (subcoronary technique) or, when using a larger aortic segment, with reimplantation of the coronary vessels. The aorta or the left atrium is then closed and the heart-lung machine is removed. Then, when the heart beats again, the pericardium and chest are closed.

Selection of the valve prosthesis

Basically, a distinction is made between two types of heart valve prostheses: Mechanical valves are manufactured artificially and consist mainly of metal, biological valves (tissue valves) are available as transplants from humans or animals.

Mechanical and biological valve prostheses differ in a number of ways that are used to select the most suitable valve for the patient. Mechanical heart valves have a much longer service life than biological valve prostheses. In laboratory tests, mechanical heart valves have achieved a (theoretical) durability of 100 to 300 years. This information refers to the number of opening and closing processes calculated on the normal heart rate of 60 to 80 beats per minute. The lifespan of biological heart valves is limited because they are subject to an accelerated aging process (calcification) compared to their own tissue. After a few years, this can lead to visible and functionally significant functional disorders that require replacement. Experience has shown that biological heart valves calcify earlier and faster in children than in adults. A major disadvantage of mechanical valves is the coagulation-activating metal surface. This leads to an increased risk of thrombosis and thromboembolism and makes lifelong anticoagulation necessary.

In principle, mechanical valves are used in patients who have a long life expectancy and for whom there is no contraindication for anticoagulation. The decision as to which type of valve prosthesis to use, however, is always based on an individual weighing of all advantages and disadvantages for the individual patient.

Mechanical heart valves

Double-leaved mechanical heart valve

Mechanical heart valves come in a variety of designs and sizes, all of which have design-related advantages and disadvantages. A distinction is made between ball, disc and double wing valves. Mechanical flaps basically consist of a metal body and a frame that is provided with a polyester sleeve. All mechanical designs cause a more or less audible valve noise (“prosthesis click”). This noise occurs when the flap closes when the flap wing (s) hit the flap ring. The clarity of this sound is an indication of whether deposits have formed on the flap. All mechanical valves produce a strong reflection and a sound shadow in sonography .

Designs (selection)
  • Tilting disc flaps (with tilting disc valves)
    • St. Jude Medical : double-leaf flap (since 1977)
    • Björk-Shiley prosthesis: single-wing valve (suspended discus, since 1968)
    • Lillehei-Kaster prosthesis: named after Clarence Walton Lillehei
    • Medtronic Hall : single-leaf valve (disc with central hole). The disc moves on a curved spike within the valve ring. The flap ring is a milled titanium monoblock.
  • Ball valve, cage valve
    • Rigid Edwards ball valve (the oldest cage valve): Ball cage prosthesis (first used in 1952). A plastic ball, which moves freely to and fro with the blood flow in a wire cage, serves as the valve or closure body. This was the first artificial valve type and is now (almost) of no importance, as this variant has significant disadvantages due to the weight of the valve ( hemolysis ).
    • Smeloff cutter ball valve

Biological heart valves

Tissue engineered heart valve

In biological valves, which in principle carry out the sail movements of normal heart valves, the valve tissue consists of human ( allo- or homograft ) or animal ( xenograft ) tissue. In what is known as tissue engineering , scaffolding structures are populated with the patient's own cells in the bioreactor. These artificially populated valves do not yet play a significant role in everyday clinical practice, but are part of everyday clinical practice at the Hanover Medical School, for example. The actual valve tissue is located in a lattice tube ("stent") or on a framework structure ("scaffold") or used without a framework. Just like artificial heart valves, biological valves that are sewn in are also surrounded by a polyester sleeve. Animal and human donor valves must be preserved after removal for later implantation. Here, cryopreservation in liquid nitrogen has established itself as the most effective method. Alternatives are preparation in an antibiotic solution at 4 ° C, X-ray irradiation and dry freezing. In the case of decellularized homografts , the donor's cells are removed from the heart valve beforehand by washing processes.

Tissue valves either have a stent implant (scaffold) or they are stentless. Stented flaps are available in sizes from 19mm to 29mm. Stentless valves are sewn directly to the aortic root. The main advantage of stentless valves is that they limit the mismatch between the patient and the prosthesis (if the surface area of ​​the valve prosthesis is too small in relation to the patient's size, it increases the pressure within the valve) so that they are useful for small aortic roots could be. Their disadvantage is that implanting stentless valves is more time consuming than stented valves

Tissue valves can last 10–20 years. However, they tend to deteriorate more quickly in younger patients. New ways have been explored to preserve tissue longer. Such a preservation treatment is now being used on a commercially available tissue heart valve. In sheep and rabbit studies, the tissue (called RESILIA ™ tissue) showed less calcification than the control tissue. However, data on the long-term shelf life in patients are not yet available.

Types of bioprostheses that have existed for some time are, for example, the Hancock bioprosthesis, the Hancock conduit and the Ionescu-Shiley bioprosthesis as well as the biological Carpentier Edwards valves.

The relatively new Ozaki procedure, named after the Japanese doctor Shigeyuki Ozaki, can be used in the aortic position. In the course of the operation, the valve leaflets are recreated from pericardial tissue and inserted into the patient's own aortic valve ring.

Ross operation

The Ross operation is a special form. This procedure is mainly used in children and young adults. If an aortic vitium is present, the aortic valve is removed and replaced by the patient's own pulmonary valve . The pulmonary valve can then be replaced by a biological valve due to the lower pressure load.

Minimally invasive procedures

Transcatheter Aortic Valve Implantation (TAVI)

In addition to the open surgical technique, there is a catheter-supported procedure in which an access route via the inguinal artery (transfemoral) or via the apex of the heart (transapical) is selected. This method is Trans aortic valve (engl. Transcatheter aortic valve implantation , TAVI) or endovascular aortic valve replacement called. The aortic valve is placed in a metal frame. The valve is brought into position using a catheter. Then it is unfolded and thereby anchored in the valve ring. The body's own aortic valve is not removed, but displaced by the prosthesis. A distinction is made between self-expanding valves and those which - comparable to a PTCA - are expanded by means of a balloon.

The technique was first described by Alain Cribier and colleagues in 2002. The aim of the TAVI is to be able to offer an aortic valve replacement to patients whose surgical risk for an open surgical replacement is rated too high; Gradually, the indication will also be extended to patients with a medium surgical risk for study purposes. However, the minimally invasive form of therapy is not yet a general substitute for the open surgical technique. Long-term results for transcatheter aortic valve implantation are not yet available due to the novelty of the procedure, but initial results from 5-year analyzes suggest that the hemodynamics and stability of the TAVI valves appear to be equivalent to surgically implanted aortic valves. In 2014, the German Society for Cardiology published quality standards for performing TAVI - one of the most important requirements is that the procedure should take place in a hybrid operating room and that a cardiac surgeon should be available.

The use of the TAVI can be associated with the following risks

  • increased risk of stroke
  • Complications when inserting the prosthesis through the vessels, such as vascular injuries
  • Need for further intervention, e.g. B. through leaks between the prosthesis and the vessel wall
  • complete atrioventricular block requiring implantation of a pacemaker

Major manufacturers are:

Aftercare

Postoperative phase

After the operation, the patient is first monitored in the intensive care unit . Artificial ventilation is ended here. In the further course, the patient is cared for in a cardiac surgery or cardiological normal ward. The one to two week stay in the acute hospital is usually followed by several weeks of rehabilitation with controlled increasing physical exertion. You can return to work around ten to twelve weeks after the operation.

Follow-up checks

Echocardiography plays a decisive role in assessing the postoperative course , as the valve function (tightness, pressure gradient) and, especially in the case of biological valves, the valve morphology can be assessed here. The first follow-up should be done after about three months.

Anticoagulation

If a mechanical heart valve replacement is used, lifelong anticoagulation must be carried out. For this purpose, coumarin derivatives such as phenprocoumon and warfarin are used. The desired INR depends on the position of the prosthesis. Anticoagulation is necessary for three months after biological valve replacement. According to TAVI, the use of platelet aggregation inhibitors is recommended.

Endocarditis prophylaxis

After heart valve replacement, lifelong endocarditis prophylaxis is recommended for all interventions in the oropharynx (e.g. dental surgery, tonsillectomy).

See also

literature

  • Martin Steiner: Assessment of biological and mechanical heart valve prostheses using time-resolved methods (dissertation) . VVB Laufersweiler Verlag, Gießen 2005, ISBN 3-89687-053-X , p. 319 .
  • Michael J. Eichler: In vitro cavitation studies on mechanical heart valve prostheses (dissertation) . Logos Verlag, Berlin 2003, ISBN 3-8325-0398-6 , p. 175 .
  • Klaus Holldack, Klaus Gahl: Auscultation and percussion. Inspection and palpation. Thieme, Stuttgart 1955; 10th, revised edition ibid 1986, ISBN 3-13-352410-0 , p. 180 f. ( Sounds and noises from artificial heart valves ).

Individual evidence

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Web links

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