The pulmonary valve regulates blood flow from the right ventricle into the pulmonary trunk. It is a semilunar valve composed of three cusps that prevent retrograde flow during ventricular diastole.
Location and Relations
The pulmonary valve is located at the opening of the right ventricle into the pulmonary trunk, approximately at the level of the third costal cartilage. It is the most superior and anterior of the cardiac valves.
The pulmonary valve is related to:
- Inferiorly: Right ventricle (infundibulum)
- Superiorly: Pulmonary trunk
- Posteriorly: Left atrium and aortic valve
- Anteriorly: Anterior chest wall (behind the third costal cartilage)
- Right: Right coronary artery and right atrial appendage
- Left: Left atrial appendage and left coronary artery
Components of the Pulmonary Valve
Annulus
The pulmonary annulus is a fibrous ring that supports the valve cusps. It is part of the cardiac skeleton. The annulus is less robust than the aortic annulus and is more susceptible to dilation.
Cusps (Leaflets)
The pulmonary valve has three semilunar cusps, named for their relationship to the pulmonary artery:
Anterior Cusp: Located anteriorly, adjacent to the anterior chest wall.
Left Cusp: Located posterosuperiorly, adjacent to the left atrium.
Right Cusp: Located posteroinferiorly, adjacent to the aortic root.
Each cusp is crescent-shaped with:
- Free edge: Thin and flexible
- Lunula: Thin, translucent region near the free edge
- Nodule of Arantius (nodulus): Thickened central region at the free edge, providing complete coaptation
- Base: Attached to the annulus in a curved line
- Ventricular surface: Smooth, facing the right ventricle
- Pulmonary surface: Facing the pulmonary trunk
Sinuses of the Pulmonary Valve
Behind each cusp is a dilation of the pulmonary trunk wall called a pulmonary sinus. Unlike the aortic sinuses, the pulmonary sinuses do not typically give rise to coronary arteries.
Commissures
The three commissures are the points where adjacent cusps meet at the annulus. They are located at the apices of the interleaflet triangles.
Function
The pulmonary valve opens during ventricular systole, allowing blood from the right ventricle to enter the pulmonary trunk. It closes at the end of systole to prevent reverse flow.
Opening: When right ventricular pressure exceeds pulmonary arterial pressure (approximately 15-25 mmHg), the valve opens.
Closing: When the right ventricle relaxes, the pressure gradient reverses, causing the valve cusps to fill and coapt centrally.
The pulmonary valve opens earlier and closes later than the aortic valve due to the lower pressure in the pulmonary circulation.
Normal Dimensions
- Annular diameter: 2-2.5 cm
- Valve area: Approximately 3-4 cm²
- Peak systolic gradient (normal): < 25 mmHg
Differences from the Aortic Valve
The pulmonary valve shares the same semilunar structure as the aortic valve but differs in several respects:
| Feature | Pulmonary Valve | Aortic Valve |
|---|---|---|
| Position | Anterior, superior | Posterior, central |
| Annulus | Less robust | Thicker |
| Coronary ostia | None | Present in left/right sinuses |
| Pressure load | Low pressure (~25 mmHg) | High pressure (~120 mmHg) |
| Cusp thickness | Thinner | Thicker |
| Nodules | More prominent | Less prominent |
Clinical Significance
Pulmonary Stenosis
Narrowing of the pulmonary valve, most commonly congenital. The cusps may be fused, dysplastic, or the annulus may be hypoplastic.
Types:
- Valvular stenosis: Most common, dome-shaped valve with fused commissures
- Subvalvular stenosis: Infundibular narrowing below the valve
- Supravalvular stenosis: Narrowing above the valve
Presents with a harsh systolic ejection murmur at the left upper sternal border, right ventricular hypertrophy, and if severe, right heart failure.
Pulmonary Regurgitation
Leakage of the valve during diastole, most commonly after surgical repair of tetralogy of Fallot (transannular patch). Also seen in pulmonary hypertension, endocarditis, and carcinoid syndrome.
Mild regurgitation is usually well tolerated. Severe chronic regurgitation leads to right ventricular volume overload and eventually right heart failure.
Congenital Anomalies
- Bicuspid pulmonary valve: Less common than bicuspid aortic valve
- Unicuspid valve: Rare, usually stenotic
- Quadricuspid valve: Very rare, usually normal function
- Pulmonary atresia: Complete absence of the valve, part of tetralogy of Fallot spectrum
Carcinoid Heart Disease
The pulmonary valve is characteristically affected in carcinoid syndrome, with plaque-like deposits causing thickening, retraction, and mixed stenosis-regurgitation. The right-sided valves are predominantly affected because the liver inactivates the vasoactive substances.
Infective Endocarditis
Less common on the pulmonary valve than left-sided valves. Risk factors include congenital heart disease, indwelling catheters, and IV drug use.