Tricuspid Valve: Structure, Function & Diseases

The tricuspid valve is one of the four valves of the heart. It forms the valve between the right atrium and right ventricle and prevents blood from flowing back into the right atrium during contraction of the ventricle (systole). During relaxation (diastole), the tricuspid valve is open, allowing blood to flow from the right atrium into the right ventricle.

What is the tricuspid valve?

The tricuspid valve is the heart valve that acts as a valve between the right atrium and the right ventricle to ensure that blood is pumped into the pulmonary artery, into the pulmonary circulation – also called the small circulation – during the right ventricle’s contraction phase (systole) and cannot flow back into the right atrium. The valve is closed during this process and only opens again during the relaxation phase of the right ventricle (diastole). Like its counterpart in the left ventricle, the tricuspid valve corresponds to a so-called leaflet valve, which in principle functions passively like a check valve, but is muscularly supported by tendon filaments on its leaflets. It is part of the four-valve system of the heart, with the help of which the closed blood circulation can only flow in a certain direction. The other two heart valves, the pulmonary valve and the aortic valve, serve to prevent blood from flowing back from the arteries into the ventricles after the ventricles have been under tension.

Anatomy and structure

The tricuspid valve is also called the leaflet valve for anatomic reasons because it consists of three leaflets (cuspis) that serve as the closure mechanism. The three leaflets are named cuspis angularis, cuspis parietalis, and cuspis septalis. Each of these sails is connected to one of the three papillary muscles by means of several, partially branching, chordae tendineae. The papillary muscles are small inward protrusions of the ventricular muscles, which can also be stimulated to contract by the electrical excitation of the ventricular muscles, slightly offset in time. Contraction of the papillary muscles causes the tendon sutures to tighten. Because the individual leaflets are thin and the cross-section of the valve is relatively large in relation to the stiffness of the leaflets, there is a risk that the leaflets will be pushed through toward the atrium after the valve closes and pressure builds up in the ventricle, thereby losing their function. The taut chordae prevent this. They serve as a built-in safety system, so to speak, to ensure that the tricuspid valve remains functional during systole. The counterpart of the tricuspid valve in the left ventricle is the mitral valve, which also functions as a leaflet valve. However, it has only two leaflets and its chordae are stretched by only two papillary muscles. Both leaflet valves are also called atrioventricular valves.

Function and Tasks

The most important function of the tricuspid valve is its valvular function as an outlet valve of the right atrium and an inlet valve of the right ventricle. During systole of the right ventricle, it must close and ensure that blood does not return to the right atrium during this pressure phase. During diastole of the right ventricle and almost simultaneous contraction of the right atrium, the valve must open wide to allow blood from the atrium to flow as freely as possible into the ventricle and fill it. The proper functioning of the tricuspid valve, along with the proper functioning of the other three heart valves, is important for maintaining blood flow in the “proper” direction in the body. Blood, which initially enters the right atrium via the superior vena cava, collects there and flows into the right ventricle during diastole. It originates from the great systemic circulation and is therefore blood that is deoxygenated and enriched with carbon dioxide. During systole, it is pumped into the pulmonary artery so that the exchange of substances can take place in reverse in the capillaries in the alveoli. Carbon dioxide is released and oxygen is taken up.

Diseases

In principle, heart valves can have two different functional impairments called valvular defects. If the valves do not open wide enough according to the rules, it is a stenosis. The opening through which the blood must flow does not correspond to the nominal cross-section, so that a more or less severe impairment of the blood flow occurs. In the other case, the valve does not close properly.Consequently, when pressure builds up during the contraction phase, part of the blood flows back again. In relation to the tricuspid valve, this means that during systolic contraction of the ventricular muscles, a greater or lesser proportion of the blood flows back into the right atrium, which is symptomatically expressed as a loss of performance. Such leakage of the heart valves is referred to as insufficiency and is divided into different insufficiency classes according to severity. However, the tricuspid valve is much less frequently affected by valve defects than its counterpart in the left side of the heart, the mitral valve. Tricuspid valve stenosis or tricuspid valve insufficiency can be caused, for example, by inflammation of the inner lining of the heart, endocarditis. The inflammation can typically lead to shrinkage or scarring or even adhesion of the leaflets, which then become dysfunctional, typically manifesting as stenosis or insufficiency. In less common cases, tricuspid valve defects may exist from birth due to developmental abnormalities. In very rare cases, tricuspid atresia, a complete absence of the valve, may be present at birth. This means that the right atrium has no connection with the right ventricle. In this case, there is usually blood mixing between the two atria via the opening, the foramen ovalis, which is still present at birth, so that oxygen-poor blood from the systemic circulation mixes with oxygen-rich blood from the pulmonary circulation, leading to resulting problems. In severe cases, tricuspid valves can be replaced with an artificial valve.