The mitral valve or bicuspid valve ( valva atrioventricularis sinistra , valva mitralis or valva bicuspidalis ) is one of the four valves of the heart . It is located between the left atrium and the left ventricle (left ventricle), where it prevents the backflow of blood from the left ventricle into the left atrium when the ventricle contracts. Their shape resembles a miter (bishop's cap), hence the name. The term bicuspid valve is derived from the two leaflets (Latin cuspides ) that make up this leaflet valve .
The bicuspid valve ( valva bicuspidalis ) consists of two leaflets, the anterior cusp (anterior leaflet) and the posterior cusp (posterior leaflet). In veterinary anatomy, they are called cuspis septalis (septum-like sail) and cuspis parietalis (wall-type sail).
The leaflets are attached to the papillary muscles ( Mm. Papillares subauricularis and subatrialis ) and thus in the heart chamber ( Ventriculus cordis sinister ) by means of tendon threads ( Chordae tendineae ) in order to prevent the valve leaflets from folding over during systole (contraction).
The two most important diseases are mitral stenosis and mitral valve regurgitation.
With mitral stenosis , the flow is reduced due to a congenital malformation or acquired disease, such as calcification or scarring of the valve. Such a stenosis is quantified on the one hand by the remaining opening area and on the other hand by the pressure gradient that builds up over the valve.
Congenital malformations that lead to mitral stenosis are:
- The supravalvular mitral stenosis : Above the mitral valve there is a constriction in the form of a ring or a fine membrane. The membrane is formed from additional connective tissue originating in the connective tissue of the mitral cusps and lies like a cloth over the mitral valve cusps. The blood flow from the left atrium into the heart chamber is difficult. The membrane can be so delicate that only transesophageal echocardiography can detect it.
A supravalvular mitral ring alone is a very rare diagnosis. Most of the time, the mitral valve below is also malformed.
- The parachute mitral valve (parachute, "parachute"): during development only one papillary muscle (instead of two) has formed and the tendon threads (so-called chordae) that connect the valve cusps with the papillary muscle are thickened and shortened. The flow of blood from the left atrium into the heart chamber is difficult because the blood has to flow like a funnel.
The designation "parachute = parachute" is explained by the illustration for the examiner and surgeon as follows: The papillary muscle is the parachute jumper, the chordae and the flap sails are the parachute ropes and the enlarged left antechamber is the parachute.
- The hammock valve (hammock, English " hammock ") is similar to the parachute valve: Both mitral valve leaflets are clearly thickened and the tendon threads (chordae tendineae) are missing from these thickened valve leaflets to the papillary muscles, so that valve leaflets and papillary muscles are directly fused together . The free mobility of the valve leaflets is severely restricted. This leads to leakage (insufficiency) and stenosis of the mitral valve.
The term “hammock” is explained as follows: If you look at the flap from above, you will find an oval hollow that looks like a hammock instead of two delicate mitral sails that form an opening into the left ventricle.
The Hammock valve is an extremely rare valve malformation, but the parachute mitral valve is a typical valve malformation of the Shone complex . There are transitional forms between the two forms.
- The mitral valve atresia is the complete closure or the genetic non-application of the valve. It is part of the Hypoplastic Left Heart Syndrome .
Mitral valve regurgitation
With mitral regurgitation , the valve no longer closes properly.
- The cause can be, for example, tearing or relative shortening of the holding threads (chordae), perforation or overstretching of a valve leaflet and enlargement of the valve ring. The degree of insufficiency is given in degrees from I ° (mild) to IV ° (severe).
- The mitral valve prolapse as a congenital malformation can lead to a failure, but is often clinically insignificant.
In addition to "pure" stenoses and insufficiencies, there are also mixed forms with different weighting of one of the two factors. Then one speaks of the combined vitium.