Pulmonary Valve

Overview

The pulmonary valve is one of the four main valves of the heart, located at the junction between the right ventricle and the pulmonary trunk. It functions as a one-way valve that opens during ventricular systole to allow deoxygenated blood to flow into the pulmonary circulation and closes during diastole to prevent backflow into the right ventricle. Its structure and timing are essential for maintaining efficient pulmonary blood flow and overall cardiovascular stability.

Location

The pulmonary valve is situated at the outflow tract of the right ventricle, at the base of the pulmonary trunk. It is:

• Anterior and leftward compared to the aortic valve

• Just beneath the sternal end of the left third costal cartilage in surface anatomy

• Posterior to the infundibulum (conus arteriosus) of the right ventricle

It lies superior to the tricuspid valve and anterior to the aortic valve.

Structure

The pulmonary valve is a semilunar valve composed of three thin, crescent-shaped cusps:

• Left semilunar cusp

• Right semilunar cusp

• Anterior semilunar cusp

Each cusp is made of connective tissue and endothelium and contains:

• A free edge that coapts with adjacent cusps during valve closure

• A nodule at the center of the free edge to aid complete closure

• Lunulae — thin margins extending from each nodule

The valve is supported by the pulmonary annulus, a fibrous ring that anchors the cusps to the right ventricular outflow tract.

Function

The primary function of the pulmonary valve is to:

• Allow unidirectional blood flow from the right ventricle to the pulmonary trunk during systole

• Prevent regurgitation (backflow) of blood into the right ventricle during diastole

It opens as the pressure in the right ventricle exceeds that in the pulmonary trunk and closes as the ventricular pressure drops below the pressure in the pulmonary arteries.

Physiological Role(s)

The pulmonary valve contributes to several key physiological functions:

• Pressure regulation: Maintains low pulmonary artery pressure by preventing backflow, ensuring forward flow only during contraction

• Efficiency of pulmonary circulation: Supports the rhythmic filling and emptying of the right heart and pulmonary arteries

• Harmonization with cardiac cycle: Works in coordination with other heart valves to sustain effective cardiac output and pulmonary perfusion

Clinical Significance

The pulmonary valve is involved in several congenital and acquired heart conditions:

• Pulmonary Valve Stenosis: A congenital narrowing of the valve opening that restricts blood flow from the right ventricle. It causes right ventricular hypertrophy and increased workload.

• Pulmonary Valve Regurgitation: Incompetent valve closure allows blood to flow back into the right ventricle, potentially leading to right-sided volume overload and heart failure. It may result from pulmonary hypertension, valve repair, or endocarditis.

• Tetralogy of Fallot: A congenital heart defect often associated with pulmonary stenosis. Surgical correction typically includes pulmonary valvotomy or valve replacement.

• Endocarditis: Although rare, the pulmonary valve can be affected by infective endocarditis, especially in intravenous drug users or in patients with congenital defects.

• Pulmonary Valve Replacement: Performed surgically or via transcatheter approaches (e.g., Melody valve) in patients with severe dysfunction, particularly post-congenital heart disease repair.

• Auscultation: The pulmonary valve sound is best heard in the left second intercostal space near the sternal border — the pulmonary area of auscultation.

Evaluation of the pulmonary valve is commonly done using transthoracic or transesophageal echocardiography, cardiac MRI, and CT. Prompt recognition and treatment of pulmonary valve diseases can significantly improve outcomes and prevent progression to right heart failure.