Cusps of the pulmonary valve

At a glance

English

Cusps of the pulmonary valve

Latin (TA2)

Valvulae semilunares valvae trunci pulmonalis

System

Heart

Region

Thorax

In order

From the anterior semilunar leaflet of pulmonary valve to the right semilunar leaflet of pulmonary valve

About the cusps of the pulmonary valve

The pulmonary valve stands at the top of the conus arteriosus, the smooth-walled outflow funnel of the right ventricle, where the pulmonary trunk begins. It is the highest of the four heart valves and the most anterior, lying behind the left third costal cartilage near the sternum. Like the aortic valve it is semilunar: three cup-shaped cusps, each fixed to the wall by a crescent-shaped base, with no chordae or papillary muscles. Opposite each cusp the root of the pulmonary trunk bulges into a small pulmonary sinus.

Their names follow their position in the adult body: anterior, right and left. These positions arise because the outflow tracts twist during development, so that the pulmonary valve ends up in front of and to the left of the aortic valve. The right and left pulmonary cusps face the right and left cusps of the aortic valve across the narrow gap between the two great arteries, which is why the facing pairs are sometimes described together in surgery.

The three cusps are built alike. Each is a fold of endocardium on a thin fibrous core. A small nodule thickens the middle of each free edge, and thin crescent-shaped lunules lie on either side of it. When the right ventricle relaxes, blood in the pulmonary trunk falls back into the pockets, the cusps fill and meet in the centre, and the valve closes. Because pressures in the lung circulation are low, the cusps are thinner and more delicate than those of the aortic valve. Their closure forms the pulmonary part of the second heart sound, heard best in the second left intercostal space beside the sternum.

Pulmonary stenosis, a narrowing usually present from birth, is the commonest disease of this valve and is often treated by stretching it with a balloon on a catheter. It is also one feature of tetralogy of Fallot. Leakage of the valve can follow surgical repair of such defects or long-standing high pressure in the lungs. The splitting of the second heart sound on breathing in reflects the slightly later closure of these cusps.

The valve also has a place in surgery for the aortic valve. In the Ross operation a patient's own pulmonary valve, with its three cusps and a short piece of trunk, is moved into the aortic position, and a donor valve is placed where it came from. This works because the pulmonary cusps grow with a child and cope well with higher pressure once transplanted. Carcinoid disease can thicken and stiffen the cusps.