Morphology/Structure
The left atrioventricular valve is located at the orifice between the left atrium and the left ventricle. It’s almost on the same plane as the right atrioventricular valve, where it sits behind the sternum at the level of the fourth costal cartilage.
The left atrioventricular valve has two leaflets, one anterior (aortic) and one posterior (mural), both of which attach to a strong fibrocollagenous anulus. The anulus permits alterations to the conformation of the valve during the cardiac cycle. The orifice has a circumference of 7–9 cm and contraction during systole may cause up to 40% reduction in annular circumference.
The leaflets have a fibrous core and are coated with endocardium. Each leaflet has a rough, clear, and basal zone. The rough zone corresponds to the region of the free margin where it provides an attachment for the chordae tendineae. It's this region that comes into contact with the free margins of the adjacent leaflets when the valve is closed. The clear zone is smooth and more opaque and is the site of attachment of occasional chordae tendineae. The basal zone is thicker, due to increased collagen. It's the region where the leaflets insert into the anulus.
The posterior leaflet has a wider attachment and attaches to approximately two thirds of the circumference of the anulus. When the valve is shut, left atrioventricular valve has a single area of apposition termed the commissure. This contrasts with the three commissural regions found within the tricuspid, right atrioventricular valve.
Key Features/Anatomical Relations
The leaflets of the left atrioventricular valve are supported by and attached to chordae tendineae, which in turn attaches to the papillary muscles of the ventricular wall. The chordae tendineae of the left atrioventricular valve are like those found associated with the right atrioventricular valve and attach to the free edges of the leaflets to prevent prolapse. Each chordae tendineae is attached to a papillary muscle. The superior papillary muscle arises from the anterior ventricular wall, while the posterior papillary muscle arises from the diaphragmatic region of the ventricular wall.
The left atrioventricular valve can be auscultated in the fifth left intercostal space, along the midclavicular line.
Function
During ventricular systole, the anulus contracts slightly to assist with closing the valve leaflets and preventing retrograde blood flow into the left atrium.
Once atrial systole occurs a jet of blood opens the valves, the ventricle is filled, and the leaflets begin to come together, again in a passive manner. Ventricular systole follows and the papillary muscles contract, which pull the chordae tendineae and thus closes the valves by pulling the leaflets together, stopping them from eversion.
List of Clinical Correlates
- Mitral stenosis
- Mitral regurgitation
- Infective endocarditis
- Rheumatic heart disease
- Marfan’s syndrome
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Mitral Valve
Mitral valve prolapse (MVP) is a heart valve condition characterized by progressive thinning of the mitral leaflet tissue, causing leaflets to billow backward during ventricular contraction, prolapsing into the left atrium beyond their normal position of closure at the level of the mitral ring or annulus.
