Congenital pulmonary stenosis is a cardiac malformation that involves an obstruction to the flow of blood from the right ventricle to the pulmonary circulation.
It is one of the most common congenital heart diseases, with an estimated incidence of about 7–9 cases per 10,000 live births, and it can occur in isolated form or as part of more complex conditions.
The severity of the stenosis can range from mild, clinically silent forms to critical conditions with severe neonatal hemodynamic compromise.
Based on the site of the obstruction, three main variants are distinguished:
The valvular form represents the vast majority of cases and results from partial fusion of the valve leaflets, often thickened or dysplastic, which hinder systolic opening. The high-velocity jet through the narrowed orifice may lead to post-stenotic dilatation of the pulmonary trunk. The subvalvular forms, typically muscular, are less common and may be isolated or associated with other anomalies of the right outflow tract. Supravalvular stenosis, finally, is rare and may affect the main arterial trunk or the pulmonary branches, sometimes in a segmental or multifocal form.
The severity of the obstruction influences the clinical presentation. Mild and moderate forms may remain asymptomatic for a long time, discovered incidentally due to the presence of a systolic murmur. The more severe forms, particularly in neonates, may lead to a hypertrophic, non-compliant, overloaded right ventricle, and a clinical picture similar to that of pulmonary atresia, with critical reduction of antegrade flow and functional dependence on the ductus arteriosus to ensure oxygenation. In these cases, it is referred to as critical neonatal stenosis.
Congenital pulmonary stenosis may present as an isolated defect or in association with genetic syndromes and complex structural anomalies. One of the most frequent associations is with Noonan syndrome, in which the pulmonary valve is typically dysplastic, with thickened, stiff, and poorly distributed leaflets. Other syndromic conditions include multiple valvular dysplasias, conotruncal syndromes, and some forms of cardiac dysplasia related to mutations in genes of the RAS-MAPK pathway.
The prognosis is generally good in mild or moderately severe forms, which often do not require treatment other than monitoring. In the more severe forms, early treatment is essential to prevent progressive right ventricular dysfunction and the establishment of a circulation not compatible with normal growth. The first-line intervention in most cases is balloon valvuloplasty, which in the majority of patients provides a stable improvement of the pressure gradient. Infundibular, supravalvular, or complex forms may instead require a targeted surgical approach, sometimes associated with correction of other concomitant malformations.
Congenital pulmonary stenosis is a malformation of the right ventricular outflow tract that originates during embryogenesis, generally between the fifth and eighth week of gestation. During this phase, the conotruncal structures must correctly separate to give rise to the aorta and the pulmonary artery, with coordinated formation of the semilunar valves.
The most frequent cause of valvular stenosis is partial fusion or dysplasia of the valve leaflets, which prevents normal systolic opening. The leaflets appear thickened, stiff, or malformed, with a narrowed central orifice and reduced mobility, configuring the classic “dome-shaped” valve.
Infundibular forms instead derive from muscular overgrowth of the right outflow tract, with a more or less dynamic narrowing during systole. In supravalvular stenosis, which is less frequent, a developmental anomaly of the pulmonary artery wall or its main branches is found, which may be segmental or diffuse, sometimes associated with histological alterations of the vascular extracellular matrix.
In addition to direct structural causes, numerous factors have been identified that increase the likelihood of developing this anomaly. Among the most relevant is Noonan syndrome, in which pulmonary stenosis, often of the dysplastic valvular type, is a cardinal lesion. Mutations in the genes of the RAS-MAPK signaling pathway (particularly PTPN11, SOS1, RAF1) interfere with cellular proliferation and differentiation during cardiogenesis. Family history of congenital heart diseases also represents an important predisposing factor, especially among first-degree relatives.
Among environmental factors, prenatal exposure to teratogens (maternal infections such as rubella, alcohol consumption, or embryotoxic drugs), uncontrolled pre-gestational diabetes mellitus, maternal obesity, and advanced maternal age have been associated with a slightly increased risk of outflow tract anomalies, including pulmonary stenosis. However, in many cases, the malformation remains isolated and without identifiable causes.
From a pathogenetic standpoint, narrowing of the right outflow tract results in a barrier to systolic flow from the right ventricle to the pulmonary artery. This leads to an increase in the transvalvular pressure gradient and progressive concentric hypertrophy of the right ventricle as an adaptive response. Hypertrophy increases wall stiffness, reducing diastolic compliance and altering filling dynamics. In the most severe cases, systolic and diastolic dysfunction may develop, with tricuspid regurgitation due to annular dilation and increased right atrial pressures.
In neonates with critical stenosis, the valvular orifice may be so narrowed as to prevent the passage of a significant amount of antegrade flow. In these situations, pulmonary perfusion depends on the ductus arteriosus, whose physiological closure leads to a rapid drop in systemic oxygen saturation, metabolic acidosis, and hemodynamic collapse. The overloaded right atrium may generate a right-to-left shunt at the level of the foramen ovale, further worsening desaturation.
Over time, chronic obstruction can lead to myocardial remodeling, ventricular dysfunction, arrhythmias, and, in untreated cases, a progressive reduction in exercise tolerance or, in older children, syncopal episodes and risk of sudden death. The evolution is highly variable and depends on the location and severity of the stenosis, as well as the adaptive response of the right ventricle.
The clinical picture of congenital pulmonary stenosis is extremely variable and depends on three main factors: severity of the obstruction, age of the patient, and the ability of the right ventricle to adapt to the overload. In mild or moderate forms, the disease may remain silent for years, while in severe cases, particularly in the neonatal period, it may present with early signs of heart failure and hypoxemia.
The perinatal history, in critical cases, may reveal signs of respiratory distress in the first hours of life, poor sucking, apathy or irritability, and, more rarely, syncopal episodes. In some neonates, the diagnosis is already suspected during the fetal period by echocardiography, especially in the presence of a hypertrophic right ventricle or dysplastic pulmonary valve. In other cases, the discovery occurs incidentally during a pediatric check-up for a systolic murmur, in a completely asymptomatic patient.
In neonates with critical stenosis, symptoms usually appear with the physiological closure of the ductus arteriosus. Antegrade flow to the lungs becomes insufficient or absent, resulting in rapid hemodynamic compromise. The typical clinical signs include:
In infants and children with moderate or severe untreated stenosis, symptoms include:
At physical examination, the most common finding is an ejection systolic murmur audible at the second left intercostal space, radiating to the clavicle or back. In valvular forms, it may be preceded by an opening click of the pulmonary valve, particularly evident during inspiration. The second heart sound may be split or accentuated, especially in the presence of elevated right ventricular pressure. In cases of tricuspid regurgitation, a holosystolic apical or parasternal murmur may be detected.
In older children with untreated severe stenosis, signs of right ventricular hypertrophy may be observed, such as a sustained parasternal impulse, lifting of the right costal border, and sometimes jugular vein distension. In advanced cases, hepatomegaly due to systemic venous congestion or dependent edema may appear.
It is important to emphasize that in some patients, despite a significant pressure gradient, symptoms may be surprisingly mild. Conversely, a moderate stenosis in a neonate with a stiff right ventricle or dysplastic tricuspid valve may cause disproportionate clinical signs. Hemodynamic adaptation, in fact, depends not only on the anatomical degree of stenosis but also on the functional and morphological response of the right heart.
Finally, in dysplastic valvular forms associated with Noonan syndrome, the clinical picture may be complicated by early ventricular dysfunction, atrial arrhythmias, and progression of the lesion over time, making close follow-up necessary even in initially pauci-symptomatic cases.
The diagnosis of congenital pulmonary stenosis is based on the integration of clinical suspicion, physical examination, and echocardiographic imaging. In the neonatal period, suspicion arises in the presence of central cyanosis unexplained by respiratory diseases, signs of low systemic output, or presence of a systolic murmur. In older children, the detection of an ejection systolic murmur in the apparent absence of symptoms may lead to targeted investigations.
Pulse oximetry may show reduced saturations in neonates with critical stenosis, sometimes below 85%, with poor response to oxygen therapy. Arterial blood gas analysis confirms hypoxemia and may show metabolic acidosis in more advanced cases.
The electrocardiogram shows signs of right ventricular hypertrophy (right axis deviation, dominant R waves in V1), but it may be normal in mild forms.
Chest X-ray is often nonspecific: it may show a prominent pulmonary arch (in valvular forms with post-stenotic dilatation), or a heart of normal size, with variable pulmonary vascularization.
The reference examination is transthoracic echocardiography, which directly visualizes:
The use of Doppler allows measurement of the transvalvular pressure gradient, which is the main parameter to classify the severity of stenosis:
It is important to assess the presence of valvular dysplasia, tricuspid valve function, the thickness and function of the right ventricle, and the presence of any associated anomalies. In selected cases, especially for surgical planning, a cardiac magnetic resonance imaging or computed tomography may be indicated to study the anatomy of the pulmonary branches.
The indication for treatment depends on the severity of the obstruction, the presence of symptoms, and the progression of the pressure gradient. In mild forms, with gradient below 30 mmHg and absence of clinical signs, no intervention is necessary: the patient should only be monitored over time to rule out progressive worsening.
Treatment is indicated in all moderate or severe cases, especially if symptomatic. The first-choice procedure is percutaneous balloon valvuloplasty, which consists in the introduction, via venous access, of a catheter with an expandable balloon up to the pulmonary valve, which is forcibly stretched, breaking the commissural fusions. It is effective in most cases of simple valvular stenosis, with lasting anatomical and functional success in the vast majority of patients.
Complications of valvuloplasty are rare but may include residual pulmonary regurgitation, perforation, or transient cardiac arrest in the most critical neonates. In these cases, or in dysplastic forms with stiff and inextensible leaflets, valvuloplasty may be ineffective, and open-heart surgery is used, with direct commissurotomy or valvular repair.
Pure infundibular stenoses, whether dynamic or muscular, require a differentiated surgical treatment, which may include resection of hypertrophic tissue and, if necessary, patch enlargement of the right outflow tract. Similarly, supravalvular stenoses or those affecting the pulmonary branches may require vascular reconstruction with pericardial patch repair or prosthetic conduits.
The prognosis is generally excellent in isolated forms treated early. In patients undergoing neonatal or pediatric valvuloplasty, freedom from reintervention exceeds 90% at 10 years, with preserved right ventricular function in most cases. However, a portion of patients may develop chronic pulmonary regurgitation which, if significant, may require valve replacement in adolescence or adulthood.
In complex cases, with associated malformations, marked valvular dysplasia or genetic syndromes, the course may be less favorable, requiring multiple interventions, close follow-up, and multidisciplinary management. Right ventricular function, integrity of the tricuspid valve, and any residual regurgitation are the main determinants of long-term outcome.
Complications of congenital pulmonary stenosis depend on the site and severity of the obstruction, the type of treatment performed, and long-term follow-up. In untreated mild forms, the risk of complications is minimal and mainly related to the possibility of slow but constant progression of the pressure gradient over time. For this reason, even asymptomatic patients must be monitored periodically with serial echocardiograms.
In moderate or severe untreated stenoses, the main complication is the establishment of progressive right ventricular hypertrophy, which over time may evolve into systolic dysfunction and the appearance of signs of right heart failure. In older children and adolescents, ventricular arrhythmias may be observed, particularly in the presence of a dilated and fibrotic right ventricle. In the most severe cases, an increased risk of sudden death has been documented, although rare.
After percutaneous valvuloplasty, the most frequent complication is residual pulmonary regurgitation, which may present in mild-to-moderate form in most patients, but in a minority may progress to severe insufficiency with right ventricular dilatation. In such cases, surgical reintervention may be necessary in adolescence or adulthood, with valve replacement using a bioprosthesis or homograft.
Other rare but possible complications after valvuloplasty include:
After open-heart surgery, complications depend on the complexity of the intervention and include residual valvular dysfunction, recurrent stenosis, secondary tricuspid regurgitation due to right atrial dilation, and, in cases involving reconstruction of the pulmonary branches, late segmental stenoses. In addition, a higher risk of pericardial adhesions and difficulty with future access for reinterventions has been documented in patients operated on at a very early age.
Finally, in patients with associated genetic syndromes (such as Noonan), the evolution may be less predictable, with progression of the defect, appearance of other valvular anomalies or difficult-to-manage arrhythmias. The presence of severe pulmonary regurgitation, excessive right ventricular hypertrophy, or biventricular dysfunction requires long-term cardiological follow-up, with clinical, echocardiographic, and sometimes magnetic resonance monitoring.