Right atrioventricular valve [Tricuspid valve]

The right atrioventricular valve (tricuspid valve) regulates blood flow from the right atrium to the right ventricle and prevents backflow during ventricular systole. The right atrioventricular valve is situated between the right atrium and right ventricle, attached to the right atrioventricular orifice within the fibrous skeleton of the heart (annulus fibrosus). It consists of cusps (leaflets), chordae tendineae, papillary muscles, and the supporting fibrous ring.

The valve typically has three principal cusps in humans and some domestic animals (Horse), hence the name “tricuspid”:

• Septal cusp (attached to the interventricular septum)

• Parietal (mural) cusp (attached to the right ventricular free wall)

• Angular cusp (between septal and parietal cusps)

However, the number and distinctness of cusps may vary slightly between species. In some animals, the cusps are less distinctly separated and may appear as two large cusps with subdivisions, like in dogs and cats (a septal and a parietal cusp).

Each cusp has:

• A base attached to the fibrous annulus

• A free edge facing the ventricular cavity

• An atrial surface (smooth)

• A ventricular surface (rough, where tendinous cords attach)

The tendinous cords (Chordae tendineae )are fibrous cords that connect the free margins and ventricular surfaces of the cusps to papillary muscles. They prevent eversion or prolapse of the cusps into the atrium during systole. There are typically:

• Primary (marginal) chordae attaching to the free edge

• Secondary chordae attaching to the ventricular surface

• Occasionally tertiary chordae attaching directly to the ventricular wall

The papillary muscles arise from the right ventricular wall and anchor the chordae tendineae. In domestic animals, the right ventricle generally contains three main papillary muscles:

• Great (magnus) papillary muscle (from the free wall)

• Subarterial papillary muscle (near the outflow tract)

• Small papillary muscle (often associated with the septal region)

• The septal cusp may also receive chordae directly from small septal papillary projections or directly from the interventricular septum.