Cusps of the aortic valve

At a glance

English

Cusps of the aortic valve

Latin (TA2)

Valvulae semilunares valvae aortae

System

Heart

Region

Thorax

In order

From the left coronary leaflet to the non-coronary leaflet

About the cusps of the aortic valve

The aortic valve sits at the junction of the left ventricle and the ascending aorta. It is a semilunar valve: instead of the cords and papillary muscles of the atrioventricular valves, it has three pocket-like cusps whose shape alone keeps them closed. Each cusp is a thin fold of endocardium with a fibrous core, attached by a curved, U-shaped base to the wall of the aortic root and free along its upper edge. Above each cusp the aortic wall bulges outwards to form an aortic sinus.

The cusps are named after the coronary arteries. The two coronary arteries open from two of the three sinuses, so those cusps are the right coronary and left coronary cusps; the third, with no artery above it, is the non-coronary cusp. In the body the right cusp lies to the front, the left behind and to the left, and the non-coronary cusp behind and to the right, next to the interatrial septum. The non-coronary and left cusps sit above the fibrous continuity with the anterior leaflet of the mitral valve.

All three share the same build. The middle of each free edge is thickened into a small nodule, and on either side of it lies a thin crescent, the lunule. When the valve closes the nodules meet in the centre and the lunules press together, making a three-pointed seal. The points where neighbouring cusps meet at the wall are the commissures. When the ventricle contracts, blood pushes the cusps against the wall; when it relaxes, back-pressure in the aorta fills the pockets and snaps them shut. The filled sinuses also help to keep the coronary openings clear.

The valve is a frequent site of disease. A common congenital variant has only two cusps, the bicuspid aortic valve, which tends to narrow or leak earlier in life. In older people the cusps can stiffen with calcium, causing aortic stenosis, which raises the work of the left ventricle and may cause breathlessness, chest pain or fainting. Leakage, aortic regurgitation, follows damage to the cusps or widening of the aortic root. Diseased valves are replaced by open surgery or by a valve delivered through a catheter, which must be positioned so as not to block the coronary openings.

Although the valve lies behind the left half of the sternum at about the level of the third costal cartilage, its sounds carry along the aorta and are heard best in the second right intercostal space beside the sternum. Infection of the cusps, infective endocarditis, can perforate them or tear them from their attachments and cause sudden leakage.