Pulmonary valve

Article written and reviewed by Dr Luca Moretti

The pulmonary valve lies at the boundary between the right ventricular outflow tract and the pulmonary artery trunk. With each systole it allows the stroke volume destined for gas exchange to pass; at the beginning of diastole its leaflets come together and prevent the blood column from returning to the ventricle. It is the most anterior and superior of the four valves, works in the lowest-pressure circuit and, in adults without congenital heart disease, is the valve least often affected by clinically relevant valvular disease.

The pulmonary valve, however, cannot be interpreted as an isolated structure. It is part of a unit comprising the infundibulum, ventriculoarterial junction, pulmonary trunk and branches, right ventricle and pulmonary circulation; for this reason, a high velocity may originate from the valve, subvalvular muscle, the supravalvular region or the branches, whereas regurgitation may depend on diseased leaflets, annular dilatation or the surgical absence of a competent valve. Identifying the site and mechanism must therefore precede any classification of severity.

The main disorders are pulmonary valve stenosis, which is often congenital, and pulmonary regurgitation, which is common after repair of congenital heart disease or treatment of obstruction. Both alter right ventricular loading: stenosis imposes a pressure load, regurgitation a volume load; when they coexist, the physiology and thresholds of each isolated defect cannot be applied mechanically.

Pulmonary valve medicine spans the entire lifespan and changes profoundly according to the starting anatomy. A critically ill newborn, an adult with untreated stenosis, a person operated on for tetralogy of Fallot and a patient with a prosthetic conduit have different risks and goals; continuity among pediatric cardiology, adult congenital heart disease, imaging, electrophysiology, interventional cardiology and cardiac surgery is therefore an integral part of care.

Anatomy, development and relationships of the outflow tract

The normal valve has three thin semilunar leaflets inserted along an arcuate line in the pulmonary root. There is no robust circular fibrous annulus analogous to that imagined in diagrams: the leaflet hinge crosses the ventriculoarterial junction and delineates sinuses in which vortical flow promotes prompt closure. Central nodules and marginal lunules complete coaptation without chordae or papillary muscles.

Sinus nomenclature varies according to perspective. In attitudinal terms, one anterior and two posterior sinuses are described; relative to the aortic root, facing and non-facing sinuses are distinguished. This relationship matters because the aortic and pulmonary roots are adjacent and rotated, while the origin of the left coronary artery and the course of the left anterior descending artery may lie close to the outflow tract. Before placement of a stent or transcatheter prosthesis, the actual coronary distance must be known.

Upstream lies the infundibulum, a smooth muscular portion of the right ventricle that separates the tricuspid and pulmonary valves. The supraventricular crest and muscular bands modulate its geometry and contractility. The absence of fibrous continuity between the tricuspid and pulmonary valves distinguishes the right heart from the left. Reactive hypertrophy, anomalous muscle bundles or surgical sequelae can narrow the outflow tract even when the pulmonary leaflets are normal.

Downstream, the sinuses merge into the pulmonary trunk, which bifurcates into the right and left pulmonary arteries. The compliance of the pulmonary arterial tree dampens pulsatility and contributes to diastolic closure. Stenosis of the trunk, branches or peripheral arteries increases right ventricular afterload but is not pulmonary valve stenosis; in some genetic syndromes the distribution of obstruction is multiple and requires complete anatomical mapping.

During embryonic development, the common outflow tract is septated and remodeled with contributions from the conotruncal ridges, neural crest cells and endocardial cushions. The valve arises from mesenchymal swellings that are excavated and thinned. Abnormalities in this process can produce commissural fusion, dysplastic leaflets, bicuspid or quadricuspid morphology, atresia or associations with conotruncal defects.

The fetal pulmonary valve regulates a circulation in which much of the right ventricular output reaches the descending aorta through the ductus arteriosus. After birth, lung expansion and the fall in pulmonary vascular resistance rapidly transform pressures and flows. In critical stenosis, the ventricle may be unable to support pulmonary circulation and flow becomes duct-dependent; at the extreme, high right-sided pressure may be associated with abnormal coronary communications in pulmonary atresia with an intact ventricular septum.

Shape and dimensions change with growth, loading and interventions. A transannular patch used to enlarge the outflow tract in tetralogy interrupts valvular competence; a conduit between the ventricle and pulmonary artery replaces part of the native unit but can calcify, narrow or become regurgitant. The anatomical report must therefore distinguish a native valve, valvotomy, patch, conduit, homograft, bioprosthesis and stent.

Normal leaflets have a layered matrix of collagen, elastin and proteoglycans covered by endothelium. This architecture permits large deformations with minimal thickness; it is not inert tissue, because interstitial cells and mechanical signaling maintain the matrix. Inflammation, fibrosis and calcification alter its properties and mobility, but in the native pulmonary valve these degenerative processes are far less common than in the aortic valve exposed to systemic pressures.

Physiology and spectrum of disease

During systole, the rise in ventricular pressure rapidly opens the leaflets and generates laminar flow toward the pulmonary trunk. The normal valve offers minimal resistance; the gradient is low and depends on stroke volume, body size and velocity. When ventricular pressure falls below arterial pressure, brief retrograde flow fills the sinuses and brings the leaflets into coaptation. The pulmonary component of the second heart sound reflects this closure and varies physiologically with respiration.

The right ventricle is adapted to a compliant, low-impedance circuit: it has a thin wall and marked sensitivity to afterload. Chronic obstruction causes concentric hypertrophy, increased oxygen demand and, when advanced, fibrosis and dysfunction. The valvular gradient represents only part of the load: pulmonary vascular resistance, peripheral obstructions, intrathoracic pressure and arterial stiffness all contribute to ventricular work.

Typical congenital stenosis features fused commissures and leaflets that open in a dome; the dysplastic form has thick, nodular, poorly mobile tissue, often with a small annulus and a less predictable response to dilation. In critically ill newborns, hypertrophy and a poorly compliant right ventricular cavity may sustain cyanosis and dependence on an atrial-level shunt even after effective opening. In adults, mild isolated stenosis can remain stable for decades.

Minimal physiological regurgitation is common and does not represent disease. Pathological regurgitation develops mainly when a procedure has altered the leaflets or enlarged the outflow tract; other causes include pulmonary hypertension with annular dilatation, endocarditis, carcinoid disease, congenital disorders and prosthetic degeneration. Chronic backflow increases end-diastolic volume, dilates the ventricle and tricuspid annulus and may promote arrhythmias.

Pulmonary atresia is not extreme stenosis to be treated by the same rules. With an intact ventricular septum it is associated with variable degrees of right ventricular hypoplasia and possible coronary sinusoids; when accompanied by a ventricular septal defect it belongs to the tetralogy spectrum and pulmonary blood supply may depend on the ductus or major aortopulmonary collateral arteries. Reconstructive strategy is defined in congenital heart disease centers.

Acquired lesions of the native valve are rare, but the clinical context can make them decisive. Pulmonary valve endocarditis, especially in the presence of catheters, congenital heart disease or bacteremia, can cause vegetations, septic emboli and valvular destruction; carcinoid disease instead deposits fibrous plaques on the right-sided valves and often combines retraction and stenosis. Tumors, vasculitis and trauma are much more exceptional, whereas fever with recurrent pulmonary infiltrates in an at-risk patient should prompt consideration of right-sided endocarditis as the source.

A prosthesis or conduit can develop structural dysfunction, thrombosis, endocarditis, mismatch, calcification or stent fracture. Stenosis and regurgitation often coexist, while somatic growth makes a device implanted in childhood progressively undersized. Comparison with the baseline study and knowledge of the internal diameter are essential; an isolated gradient does not distinguish degenerated tissue, high flow and an obstruction upstream or downstream.

Clinical assessment and multimodality imaging

History-taking reconstructs the congenital diagnosis, procedures, vascular access, type of conduit or prosthesis, endocarditis, arrhythmias and pregnancy. Dyspnea, chest pain, syncope and reduced exercise tolerance may signal obstruction; exercise intolerance, palpitations and edema may accompany advanced regurgitation. Many patients gradually reduce their activity and describe themselves as asymptomatic: comparison with previous performance is more informative than a generic question.

Physical examination integrates the second heart sound, murmurs, parasternal impulse and signs of congestion. In valvular stenosis, an ejection click and a crescendo-decrescendo systolic murmur at the upper left sternal border are typical, with an attenuated P2 in severe disease; regurgitation instead produces an early diastolic murmur, often soft because of the low gradient and higher-pitched when pulmonary hypertension is present. Cyanosis ultimately points toward a right-to-left shunt or insufficient pulmonary blood flow.

Doppler echocardiography is the first-line examination. Parasternal short-axis, subcostal and RVOT views show doming, thickening, annulus, trunk and bifurcation; color Doppler localizes acceleration and regurgitation. Pulsed-wave Doppler identifies the initial level of velocity increase, whereas continuous-wave Doppler measures the maximum velocity along the entire beam. Oblique alignment underestimates velocity, while contamination by tricuspid regurgitation can overestimate it.

Obstruction severity is described using velocity and peak instantaneous gradient calculated with the simplified Bernoulli equation, together with mean gradient, right-sided pressure and ventricular response. The peak Doppler value is not the same as the peak-to-peak gradient measured at catheterization. Low output, right ventricular dysfunction and serial stenoses complicate interpretation; an apparently modest gradient is not reassuring if the ventricle cannot generate flow.

For regurgitation, the origin and width of the jet, duration, continuous-wave Doppler density, diastolic flow reversal in the pulmonary arteries, and right-sided dimensions and function are considered. Rapid deceleration can indicate pressure equalization but depends on compliance. Echocardiographic quantification is less validated than for left-sided valves; jet area and pressure half-time should not be used in isolation.

Cardiac magnetic resonance is the reference standard for right ventricular volumes, ejection fraction and flow. Phase-contrast imaging measures forward and reverse volume in the pulmonary trunk, calculating regurgitant fraction and volume; measurements in the branches clarify differential distribution and backflow. Shunts, collaterals, stent artifacts and plane selection can create discrepancies, which should be resolved with flow balances and quality control.

Cardiac CT provides high anatomical resolution of the outflow tract, calcifications, conduits, stents, coronary arteries and access routes. It is central to transcatheter planning: areas and perimeters throughout the cardiac cycle, landing zone, risk of coronary compression and relationships with the aorta and sternum are assessed. It does not quantify physiology as comprehensively as magnetic resonance and entails radiation and contrast, which must be justified especially in younger patients.

Cardiopulmonary exercise testing, ECG and rhythm monitoring document consequences not visible at rest. Oxygen consumption, ventilatory slope and oxygen pulse allow serial comparison; QRS duration and arrhythmias are particularly relevant after tetralogy repair. Catheterization is reserved for discrepancies, measurement of resistance, intervention or simulation of a prosthesis with coronary testing.

Therapeutic principles and valve interventions

No pharmacological therapy can correct fused leaflets or recreate an absent valve. Drugs are instead used to treat congestion, arrhythmias, endocarditis, thrombosis and conditions that increase flow or pulmonary pressure; diuretics, for example, can relieve symptoms of regurgitation but should not delay correction when progressive dilatation or dysfunction appears. The decision to intervene therefore arises from the combination of mechanism, consequences, risk and clinical trajectory.

In congenital valvular stenosis with commissures that can be separated, balloon valvuloplasty is the treatment of choice when obstruction is significant and requires intervention. The balloon separates commissures, reduces the gradient and preserves the valve, but may generate regurgitation; dysplastic leaflets, a hypoplastic annulus and subvalvular obstruction reduce success. Surgery is indicated when anatomy is unfavorable, associated lesions are present or catheter treatment fails.

In the critically ill newborn, the immediate objective is to stabilize oxygenation and cardiac output, maintaining ductal patency with prostaglandin when necessary. Opening the valve does not immediately guarantee effective biventricular circulation if the ventricle is small or stiff. Decompression, support of pulmonary blood flow, management of the atrial shunt and assessment of the coronary arteries form a unified strategy.

Regurgitation is treated with valve replacement when symptoms, exercise capacity, volumes, function, arrhythmias and associated lesions indicate that the cost of waiting exceeds that of the procedure. Surgery allows remodeling of the outflow tract and treatment of the tricuspid valve, pulmonary arteries and arrhythmias; it may use a bioprosthesis, homograft or conduit. Durability is finite and a lifetime strategy must anticipate likely reinterventions.

Transcatheter implantation is established for dysfunctional conduits and bioprostheses and has expanded to selected native outflow tracts with dedicated devices. Before implantation, anchoring, diameter, calcification, access and the risk of rupture or coronary compression are assessed. Balloon testing with simultaneous coronary angiography may be necessary; unsafe anatomy remains an indication for surgery.

The choice between surgery and catheter intervention is not simply a ranking of invasiveness. A young patient with an aneurysmal outflow tract, branch stenoses, severe tricuspid disease and an arrhythmic substrate may benefit from comprehensive surgical correction; a patient with a cylindrical conduit and previous sternotomies may avoid another operation. Active endocarditis, thrombus, inadequate access and the need for concomitant procedures change the balance.

Endocarditis prophylaxis follows high-risk categories, particularly patients with prosthetic material, together with oral hygiene and treatment of bacteremia. After a transcatheter or surgical valve, antithrombotic therapy and follow-up depend on the device and context; regimens studied in the aortic position are not automatically transferable. Persistent fever, a new gradient or new regurgitation requires early assessment.

Lifelong surveillance

Follow-up is proportional to severity and history. Mild isolated stenosis may require widely spaced reviews; moderate disease, significant regurgitation, a reconstructed outflow tract or a prosthesis requires regular specialist surveillance. Each assessment compares symptoms, activity, auscultation, ECG, velocity, regurgitation, right-sided pressure, dimensions and function, without allowing a single parameter to govern the decision.

In children, gradients and dimensions must be interpreted together with growth and body surface area. A small annulus may grow after valvuloplasty, whereas conduits and prostheses retain a fixed diameter and become progressively more restrictive; Z-scores, oxygen saturation, weight curve and development therefore complete the hemodynamic interpretation. In adults, by contrast, new symptoms may reflect late consequences or acquired disease and should not automatically be attributed to known congenital heart disease.

In patients with congenital heart disease, magnetic resonance is repeated when echocardiography does not quantify the ventricle reliably or when the values may change timing. Volumetric thresholds proposed for repaired tetralogy are indicators of risk and reversibility, not universal numbers for every pulmonary regurgitation. Original diagnosis, sex, body surface area, scar, residual obstruction and left ventricular function modify their meaning.

Surveillance of a prosthesis starts with a post-implantation baseline examination. A subsequent rise in gradient, new regurgitation, leaflet thickening or a clinical change prompts evaluation for thrombosis, degeneration, endocarditis and growth. CT and fluoroscopy can clarify mobility and stent integrity; blood cultures and metabolic imaging are selective tools, not substitutes for clinical assessment.

Pregnancy and exercise require individualized assessment. Severe stenosis limits the increase in cardiac output and should be treated before conception when indicated; isolated regurgitation is often tolerated as long as right ventricular function is preserved, but arrhythmias and congestion require a plan. Sports participation depends on gradient, pressure, function, rhythm and associated lesions, not on the diagnostic label alone.

Transition from pediatric to adult care must preserve operative records, measurements, images and device information. Loss to follow-up during an asymptomatic phase risks late presentation with a dilated ventricle or deteriorated prosthesis. Education about fever, syncope, palpitations and declining exercise capacity allows earlier reassessment without medicalizing every physiological variation.

Prognosis is excellent in well-treated isolated stenosis, but remains related to residual regurgitation, right ventricular function and reinterventions. In complex congenital heart disease, the valve is one determinant among scars, pulmonary branches, ventricles and arrhythmias. The best outcome does not simply mean a low gradient or absence of backflow: it includes preservation of the ventricle, functional capacity, device durability and the feasibility of future interventions. Continuity of surveillance allows each procedure to be chosen when hemodynamic benefit and expected durability are most favorable.