Cardiology

Heart valve surgery: current approaches

Marina Virko
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The need for a heart valve procedure occurs when it fails to cope with its function due to various circumstances. In such cases, cardiac surgeons come to the rescue.

Why do some patients have to undergo heart valve surgery?

Acquired, i.e., developing during the lifetime, heart valve diseases can occur for a variety of reasons. In addition to wear and tear, the valves often suffer from other factors, such as calcification (sclerosis), cholesterol deposits, bacterial inflammation, rheumatic fever, heart attack, etc. In addition, there is a large group of congenital valve disorders.

All these factors lead to abnormal changes in the anatomy of the affected organ and, as a consequence, to its malfunction.

The abnormality consists in the incorrect blood flow between the heart chambers and, consequently, the release of blood into the general circulatory system.

When there is a significant narrowing of the opening between the heart chambers due to, for example, valve sclerosis, doctors speak about stenosis. If the valve fails to close the opening between the chambers properly (which can be caused not only by the valve itself, but also by various reasons related to changes in the size of the heart chambers), we are dealing with valve failure (regurgitation).

Both issues gradually lead to significant abnormal changes in blood flow, heart muscle overload, and its gradual weakening.

At first, these developments may remain imperceptible, causing no obvious symptoms. But over time, the heart becomes so overstressed that it ceases to cope with its work. The weakening of the heart muscle is life-threatening. The medications that support it become less and less effective. Thus, one is confronted by a situation where the only solution is heart surgery – either the reconstruction or replacement of the diseased valve.

What procedures can be used to treat heart valve disorders?

If surgery becomes unavoidable, cardiac surgeons first decide whether the patient's own valve can be preserved by "repairing" it, or whether the organ must be removed and an artificial one implanted instead.

Should the latter be preferred, the individual arguments in favor of one or another type of prosthesis are to be weighed very carefully. Basically, there are two types - mechanical or biological. The decision is always made collectively by cardiologists, cardiac surgeons and anesthesiologists together with the patient, with whom the pros and cons are discussed.

How are artificial heart valves created, and what types are there?

The history of prosthetic heart valves dates back to 1952, when US surgeon Charles Hufnagel first implanted an artificial aortic valve in a severely ill 30-year-old woman. The patient survived and returned to normal life.

Since then, valve surgery has progressed steadily. Doctors, engineers, chemists, and other specialists have continually improved surgical techniques and the materials used to make prostheses.

Today, valve replacement has become quite a routine procedure at specialized cardiac surgery facilities.

Various implant modifications have allowed hundreds of thousands of people to return to a full life. The most common type of such surgery is aortic valve replacement. In Germany alone, more than 200,000 patients have already had this "spare part" implanted. Over 30,000 such operations are performed each year. The number of patients in need of an artificial heart valve implant is increasing steadily, not least because of the growing life expectancy.

Inventors have already developed more than 80 implant models made of metal, synthetic composites, textiles or animal tissues; with wings, caged balls and flaps. All of them present a combination of high technology and handiwork. Each such prosthesis is a small technical marvel.

Just like real valves, the prostheses allow blood to flow only in the intended direction - either inside both ventricles or out again. Between two heart beats, the valves close and prevent backflow of blood.

Mechanical heart valve prostheses are made entirely of artificial materials. To ensure a "non-return valve" function (i.e., to prevent backflow), the so-called bileaflet design is most often used. Two semi-circular flaps, attached to a rigid ring, swing open and close, like the doors of cowboy saloons in the Wild West movies. The flaps and ring are made of synthetic material, mostly extremely strong pyrolytic carbon, and framed by a polyester cuff.

Biological heart valve prostheses use material of animal origin – porcine heart valve tissue or calf pericardium.

Under special conditions and using a microscope, it is sewn onto a wire frame by hand. In the production process, the tissue is first chemically treated in order to prolong the viability of the prosthesis and prevent host reaction.

In 2022, scientists at the University of Munich produced a heart valve on a three-dimensional printer. For this purpose, an advanced additive (i.e., creating an object from an electronic model) technology called "melt electrowriting" (MEW) was used. It is expected that in the future prostheses will be created in this way, growing with the body, so they can also be used in children.

Advantages and disadvantages of mechanical and biological prostheses

A huge "pro" of mechanical heart valves is their durability. These models last practically for life. The likelihood that the flap will break is extremely low, occurring in about one in 10,000 people who undergo such surgery. The disadvantage of synthetic implants, however, is that there are favorable conditions for thrombus formation on their surface. Therefore, to prevent the possible consequences of clotting, such as the development of a stroke, those who have such prostheses must take blood thinning medications (marcumar, warfarin, etc.) throughout their lifetime.

Also, according to a 2017 study by Norwegian scientists, one in six patients with an artificial valve feels a metallic clicking sound when the valve slams shut.

This is not the case with biological prostheses. With them, anticoagulation therapy is needed only for a certain period. After it, low doses of aspirin are sufficient.

But the disadvantage of animal tissue implants is their relatively short lifespan. From 10 to 15 years after placement, the prosthesis calcifies or undergoes a natural process of wear and tear, so that it must be replaced.

It has been determined that the younger the patient, the shorter the life span of the biological prosthesis.

Among other things, this is also due to the fact that the heart is more stressed in young people. Therefore, cardiac surgeons prefer durable mechanical implants for patients under 65 years of age. For those over 65, the biological model becomes preferable because it does not require continuous blood thinning therapy. However, some heart surgery centers lower this threshold to 55 years, because a possible follow-up surgery to replace the prosthesis can be less challenging.

How is heart valve reconstruction performed?

In the case of aortic regurgitation, the valve is usually reconstructed by minimally invasive method through cutting only the upper third of the sternum. The "repair" type itself depends on the underlying disease that led to the insufficiency. In many cases normal function is restored by reducing the ring and reconstructing the cusps. In cases of aortic aneurysm, it is replaced by a vascular prosthesis made of artificial material, in which the own aortic valve is sewn.

A major advantage of the aortic valve reconstructive procedures compared to its prosthetics is that there is no need for long-term anticoagulation drugs.

Reconstruction of the insufficient mitral valve, as a rule, is performed also in a minimally invasive way (minimally invasive thoracotomy). The procedure is performed through the intercostal space without damaging the sternum. The treatment usually includes fibrous valve ring annuloplasty and replacement of torn tissues.

The advantages of mitral valve repair include giving up blood thinning medications 3 months after the operation, very good long-term results, and very low inflammation risks in later life.

In patients with dilated left heart chamber, innovative surgical techniques based on changing the geometry of the heart chamber are used today.

Tricuspid valve reconstruction is also a minimally invasive procedure. The most common cause of tricuspid valve leakage is right atrial enlargement. In most cases, tricuspid valve repair is limited to ring annuloplasty. The advantages are the same as in mitral valve reconstruction.

What are the ways in which heart valve interventions are performed?

The gold standard of operations involving artificial valve implantation or valve reconstruction is open surgery.

At the same time, modern cardiac surgery very often uses minimally invasive techniques with a partial incision of the upper part of the sternum. This method allows to sustain good stability of the chest, and has a good cosmetic result. These surgeries are performed using a heart-lung machine which ensures a constant blood circulation for as long as the surgeon repairs or replaces the heart valve.

This type of intervention is still very common due to the very good long-term results and low surgical risks.

However, a 2-3-hour operation under general anesthesia can only be tolerated by patients who are strong enough. In 2002, doctors found an alternative. The procedure is called TAVI (transcatheter aortic valve implantation). The procedure is performed under local anesthesia. The surgeon "advances" the folded artificial valve into the heart through the groin artery. The diseased valve remains in the body, it is simply moved sideways with the implant.

Developed originally for severely ill patients, due to its successful results TAVI has come into use in younger ones.

Thus, in 2019 as many as about 60% of all aortic valve replacements were performed via catheter. However, it must be taken into account that the new valve can put pressure on the conduction pathways that determine the heart rhythm, so about 10% of those who underwent this operation later need an artificial cardiac pacemaker installed. With the conventional technique, this figure is half as much. Strokes are also somewhat more common after TAVI, although overall those are very rare.

Since 2008, catheter procedures have also been used in mitral valve treatment. The most common of these is currently MitraClip, it has been performed in more than 100,000 patients worldwide. The MitraClip is the patented name of a clip device that is delivered to the heart via a flexible tube (catheter) inserted through the inguinal vein. There, the clip attaches to the two valve flaps, locking them in an optimal position. Thus, regurgitation is stopped. In 2019, an improved modification of this operation, the PASCAL technique, was introduced. Later came the Cardioband, which is performed according to the same algorithm, but to restore tightness in this case an implant (a ring attached to the fibrous ring of the mitral valve) is installed.

In certain cases of aortic valve replacement, e.g., in very young patients for whom the continuous administration of blood thinning medications is undesirable or impossible (e.g., women who still want to have children), the so-called Ross operation is used. The diseased aortic valve is removed and replaced by patient’s own pulmonary valve, which is, in turn, replaced by a donor valve (homograft). This type of intervention is also a good option for young, athletically active patients who do not want any limitations in their quality of life.

Finding the best solution together

It is not always easy and quick to determine which procedure and implant type is the best in each individual case. Therefore, such decisions are always made jointly by cardiac surgeons, cardiologists, and anesthesiologists. If necessary, other specialists also get involved.

The opinion of a competent independent expert can be of invaluable help to the patient and the treating physician.

To obtain such an assessment one does not to undergo all exams once again. As a rule, the available findings and reports are sufficient to get a second opinion and make the final decision.

References

  1. Echte Handarbeit. FOCUS Gesundheit Nr.93 – Herz & Kreislauf. ISSN 2199-5087
  2. Filippo Calì MD, Matteo Pagnesi MD, Elisa Pezzola MD, Andrea Montisci MD, Marco Metra MD, Marianna Adamo MD. Transcatheter edge-to-edge mitral valve repair for post-myocardial infarction papillary muscle rupture and acute heart failure: A systematic review. Wiley Online Library, 10 May 2023. | https://doi.org/10.1002/ccd.30682
  3. Totally endoscopic aortic valve replacement: Techniques and early results. Front. Cardiovasc. Med., 09 January 2023. Volume 9 - 2022 | https://doi.org/10.3389/fcvm.2022.1106845
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