Heart valves: structure and heart valve defects

The heart is the pump that keeps the human body running. The organ, which weighs 300 grams and is about the size of a fist, ensures that all organs in our body are supplied with sufficient blood. It beats about 100,000 times a day. Up to the age of 70, there are almost 2.5 billion strokes. Five to six litres of blood are pumped through the body every minute. Its anatomy (structure) is crucial for the heart to deliver this top performance. It consists mainly of muscles and is divided into four chambers that work in a perfectly coordinated manner. Small, delicate structures are essential for the blood to flow in the right direction at the right time: the heart valves. They are the valves of the heart and are crucial for its function.

How many and which heart valves does a person have?

There are four heart valves in total. Of these, two lie between the atria and ventricles of the heart; the other two are in front of the great vessels leading away from the heart, the pulmonary vein and the aorta. The two valves between the atria and ventricles are tricuspid and mitral. These are so-called sail flaps.

The two heart valves in front of the large vessels are named after them, referred to as the pulmonary and aortic valves. These two heart valves are called semilunar valves. They owe this term to their structure, similar to the sail flaps. The shape of the components of the sail flaps is more reminiscent of stretched sails, while those of the pocket flaps are similar to bags.

These are the unique features of the four heart valves:

1. The tricuspid valve is located between the right atrium and the right ventricle. It owes its name to its structure. It consists of three (Latin: tri) tips or sails (Latin: cuspis). The deoxygenated blood flows through them from the atrium into the ventricle.
2. The mitral valve is located between the left atrium and the left ventricle. Their name comes from their appearance: their shape is reminiscent of the mitre, the headgear worn by bishops in many Christian churches. But it also has a second name: analogous to the tricuspid valve; it is also referred to as the bicuspid valve since it consists of only two (Latin: bi) leaflets. Oxygen-rich blood flows through it from the left atrium into the left ventricle.
3. Pulmonary valve:  It lies between the right ventricle and the pulmonary vein. The oxygen-poor blood is pumped through them towards the lungs. It belongs to the pocket flaps and consists of three flap pockets.
4. The aortic valve marks the transition from the heart to the systemic circulation. This is where the blood starts its journey through the body’s blood vessels. It is also a pocket flap and usually consists of three flap pockets.

Structure of the heart valves

Anatomically, heart valves are part of the endocardium (the heart’s lining). A fragile skin (0.5 to 1 millimetre) lines the inside of the heart. It consists of a single layer of cells called the endothelium. Underneath are various layers of collagen and elastic connective tissue.

The flaps and pockets of the valves themselves are devoid of blood vessels. This means they do not have their blood supply but are nourished by the blood flowing past. Such tissues are also called bradytrophic (from the Greek brads = slow and trophy = nourishment). In addition to heart valves, cartilage, ligaments, eye lens, cornea, and scar tissue are also bradytrophic in the human body.

the function of the heart valves

The heart valves work like valves that allow blood to pass in one direction but prevent backflow. The opening of the respective valves is directly related to the heart’s action. It is not an active opening and closing of the flaps, such as opening a door. Instead, pressure conditions passively open and close the heart valves.

For a better understanding, the two phases of the heart action – systole (ejection phase) and diastole (filling phase) – are best considered separately.

• At the beginning of systole, the heart muscle contracts, so the pressure in the ventricles increases and eventually exceeds the pressure in the atria, causing the leaflet valves to close. This prevents blood from backflowing from the ventricles into the atria.
• All four valves are closed until the pressure in the chambers becomes so great that the semilunar valves (pulmonary and aortic valves) open due to the high pressure. The blood can flow from the chambers into the aorta and the pulmonary vein. During this time, the sail flaps remain closed. Their “breakthrough” into the atria is prevented by the papillary muscles, which are connected to the cusps of the valve flaps via the so-called tendon threads (chordae tendineae).
• When the contraction ends during diastole, the pressure in the ventricles drops again until it is lower than in the pulmonary vein or aorta. When this point is reached, the pocket flaps close again.
• Here, too, all four heart valves are closed again for fractions of a second. If the ventricular pressure falls even further, below that in the atria, the leaflets open, and blood flows from the atria into the ventricles.
• The heart muscle contracts again, and a new heart action begins.

 

Diseases of the heart valves

Most heart valve diseases are diseases that occur in the course of life. They are, therefore, also referred to as acquired. The frequency increases significantly with age. About 2 per cent of the 55-year-olds and 13 per cent of the over 75-year-olds are affected. Men are nearly three times more likely to develop heart valve defects than women.

Two large groups of problems with the heart valves can be distinguished:

• Heart valve stenosis: The opening of the heart valves is narrowed. This means that less blood can flow through it than usual. Aortic valve stenosis is the most common heart valve defect requiring treatment. It is common in older people who have a hardened heart valve.
• Heart valve insufficiency: A heart valve leaks and does not close properly. The backflow of blood is, therefore, not reliably prevented. Instead, more or less, blood flows in the “wrong” direction. Mitral regurgitation is the most common but requires less treatment than aortic stenosis. Aortic valve insufficiency is the third most common heart valve defect.

Diseases of the pulmonary or tricuspid valve are sporadic. This is because the pressure conditions in the right heart are significantly lower, and the stress on the valves is more melancholy.

The mitral valve prolapse is a particular case. It is a primarily congenital malfunction of the mitral valve, in which parts protrude (prolapse) into the left atrium during systole. About 3 per cent of people have this abnormality, but it usually doesn’t cause symptoms and rarely requires treatment.

Cause of valvular heart disease

By far, the most common causes of heart valve disease are wear and calcification throughout life. Over the years, heart valves have been subjected to considerable stress from the constant blood flow. This can cause degenerative damage (wear damage). 

In only about 10 per cent of cases, congenital heart valve defects or system defects cause a defective heart valve. The bicuspid aortic valve, which has only two pockets instead of three, should be mentioned here. Bicuspid aortic valves are more susceptible to degenerative damage than those with three sacs.

Infections or metabolic causes are also possible, i.e. metabolic processes. Heart valve disease can be the result of a heart attack, for example. Inflammation of the heart muscle (myocarditis) or inflammation of the endocardium (endocarditis) can also damage the heart valves. In the past, mitral valve stenosis was often the result of rheumatic fever caused by streptococci. However, streptococcal infections are treated early with antibiotics, and rheumatic fever has become rare.

Consequences of heart valve defects

Regardless of stenosis or insufficiency, a disease of the heart valves leads to a strain on the heart muscle, as the heart can no longer work as efficiently as usual. A stenosis requires more pressure to push the same amount of blood through a smaller opening. This is called compression loading. In the event of an insufficiency, the volume in the ventricle or atrium is increased by the blood flowing back, referred to as volume overload.

In both cases, the result is an enlargement of the heart (hypertrophy), which, over time, can lead to heart failure (cardiac insufficiency).

 

Symptoms of heart valve disease

Mild forms of heart valve defects often cause no symptoms or only when the body is particularly stressed (e.g. due to an infection, sport, etc.). Then there are non-specific symptoms such as:

• drop in performance
• dizziness
• unconsciousness
• malaise
• heart palpitations or cardiac arrhythmias

A long-standing, untreated disease of the heart valves can then lead to the symptoms of cardiac insufficiency. These include shortness of breath, shortness of breath and water retention in the legs.

Diagnosis of heart valve diseases

In addition to questioning the person concerned about symptoms (anamnesis), the physical examination, mainly “listening” with the stethoscope, is an essential first step. If the blood flows through an opening that is too small or if there is a backflow, this causes heart murmurs that are not expected under typical flow conditions. This can be the first indication of heart valve disease.

The second step is usually an ultrasound heart scan (echocardiography). Stenosis and insufficiencies can be visualized here, and their severity can be assessed. In addition, X-rays of the chest (thorax) and an ECG are usually performed, and laboratory tests are carried out.

Treatment of heart valve defects

Heart valve diseases are usually treated surgically. The resulting cardiac insufficiency can also be treated symptomatically with medication. This is necessary if an operation is not possible or not immediately possible. In some cases, diluting the blood may also be required to improve the flow conditions. It can also be helpful to use antibiotics to prevent inflammation of the heart’s inner lining ( endocarditis ).

However, these therapeutic approaches still need to eliminate the actual anatomical problem. In the majority of cases, an operation is necessary.

 

Heart valve surgery: This is how the surgery is done

Heart valve surgery is open heart surgery. It is performed with a heart-lung machine and is associated with a not-inconsiderable risk of surgical complications. The duration of the operation is between two and three hours. Those affected should be sufficiently fit in terms of their physical condition to survive such an operation.

The recovery phase that follows also takes some time. After a heart valve operation, rehabilitation usually lasts three to four weeks and is used to build up performance slowly.

There are two approaches to surgery: the broken valve can be reconstructed or replaced. Reconstructive surgery has a slightly lower mortality rate than heart valve replacement surgery, so reconstruction is preferred in many hospitals. However, reconstructed valves have an increased risk of re-stenosis or insufficiency than replaced valves.

Heart valve replacement: Biological or artificial heart valve?

When a heart valve is replaced, there are two different options:

• Artificial heart valve (mechanical valve prosthesis): Consists of synthetic material (carbon and polyester) and is characterized by a long service life. However, lifelong blood thinning is necessary as a result.
• Biological heart valve: These are valves made from porcine or bovine tissue mounted on a metal framework. The tissue has been specially treated to prevent a rejection reaction by the immune system. As a result, immunosuppression is just as unnecessary as blood thinning. However, the lifespan of biological valves is shorter, averaging 12 years.

An alternative to the very stressful heart valve surgery for aortic valve stenosis is catheter-based valve replacement, especially in older patients. It is known as TAVI (transcatheter aortic valve implantation). Here, the broken valve is dilated with the help of a balloon (forced to the side by the expansion of the balloon) and replaced with a biological valve.

Another option is balloon dilation alone, in which the old valve is dilated, but no new heart valve is inserted. The results of this variant usually need improvement. Therefore, its use is limited to palliative or suitable for bridging until the definitive operation.