Pulmonary Atresia: Causes, Pathophysiology, Risk Factors, Clinical Features, Diagnosis, Management and Prevention

Pulmonary Atresia: Causes, Pathophysiology, Diagnosis and Management

~Introduction

Pulmonary atresia is a rare and critical congenital heart defect in which the pulmonary valve — the valve that regulates blood flow from the right ventricle to the pulmonary artery — fails to form properly. Instead of a normal valve that opens and closes, there is a solid sheet of tissue blocking the connection, preventing blood from reaching the lungs for oxygenation.

This condition leads to severe hypoxemia (low oxygen levels in the blood) and is life-threatening if not promptly diagnosed and treated. Pulmonary atresia accounts for approximately 1–3% of all congenital heart defects, with an estimated incidence of about 1 in 10,000 live births. It is more common in males and often detected soon after birth due to profound cyanosis.

There are two main forms of pulmonary atresia:

1. Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)

2. Pulmonary Atresia with Ventricular Septal Defect (PA/VSD)

Each type has different anatomical, physiological, and clinical implications, which influence management and long-term outcomes.

~Normal Cardiac Anatomy and Circulation

In a normal heart:

• The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava.

• Blood then flows through the tricuspid valve into the right ventricle.

• During ventricular contraction, the pulmonary valve opens, allowing blood to flow into the pulmonary artery, which carries it to the lungs for oxygenation.

• Oxygenated blood returns to the left atrium, passes through the mitral valve to the left ventricle, and is pumped into the aorta to supply the body.

In pulmonary atresia, the pulmonary valve is either absent or fused shut, so no direct blood flow from the right ventricle to the pulmonary artery is possible. Consequently, oxygenation depends on alternative routes, such as a patent ductus arteriosus (PDA) or other congenital shunts.

~Anatomy and Pathophysiology

1. Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)

• In this form, the ventricular septum is intact, meaning there is no opening between the right and left ventricles.

• The right ventricle is small (hypoplastic) because it has little or no blood inflow or outflow.

• Blood cannot leave the right ventricle to reach the lungs.

• Oxygenation depends on right-to-left shunting through the foramen ovale or atrial septal defect (ASD) into the left atrium.

• The pulmonary circulation is maintained through a patent ductus arteriosus (PDA), which connects the aorta to the pulmonary artery.

In severe cases, abnormal connections (sinusoids) may develop between the right ventricle and coronary arteries, potentially causing right ventricular–dependent coronary circulation, which complicates surgical repair.

2. Pulmonary Atresia with Ventricular Septal Defect (PA/VSD)

• In this type, there is a large ventricular septal defect (VSD) that allows communication between the right and left ventricles.

• The right ventricle is usually better developed than in PA/IVS.

• The pulmonary arteries may arise abnormally from multiple sources, including major aortopulmonary collateral arteries (MAPCAs).

• The overall physiology resembles Tetralogy of Fallot with pulmonary atresia, where blood flow to the lungs depends on these collaterals or a PDA.

In both types, the fundamental problem is absence of normal antegrade flow to the lungs, forcing the heart to rely on alternative pathways to oxygenate blood.

~Classification

1. Based on Ventricular Septum

• Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)

• Pulmonary Atresia with Ventricular Septal Defect (PA/VSD)

2. Based on Pulmonary Artery Anatomy

• Confluent pulmonary arteries — right and left arteries connected

• Non-confluent pulmonary arteries — separated, supplied by collateral arteries

3. Based on Coronary Circulation (in PA/IVS)

• Normal coronary arteries

• Right ventricle–dependent coronary circulation

~Etiology and Risk Factors

The exact cause of pulmonary atresia is unknown, but it arises due to abnormal development of the right ventricular outflow tract and pulmonary valve during embryogenesis. Several factors may contribute:

• Genetic abnormalities: Chromosomal defects (e.g., 22q11 deletion, trisomy 13, 18, or 21)

• Maternal factors:

  • Diabetes mellitus

  • Viral infections (rubella)

  • Exposure to teratogenic drugs (lithium, retinoic acid)

  • Alcohol and smoking during pregnancy

• Familial predisposition: Rare, but congenital heart diseases may occur in siblings.

There is no known prevention, but prenatal screening and genetic counseling can help detect and prepare for management before birth.

~Pathophysiology

The absence of a pulmonary valve results in complete obstruction of blood flow from the right ventricle to the lungs. Consequently:

• Deoxygenated blood returning to the right atrium cannot enter the pulmonary artery.

• Blood passes through an atrial communication (PFO or ASD) into the left atrium, mixing with oxygenated blood.

• The left ventricle must pump mixed blood to both systemic and pulmonary circulations.

• Pulmonary blood flow depends on PDA or aortopulmonary collaterals.

• Without these alternate routes, oxygenation is critically compromised.

In PA/IVS, the small right ventricle experiences high pressure, and blood may backflow through coronary sinusoids, leading to potential myocardial ischemia.
In PA/VSD, pulmonary blood flow varies — it may be excessive (causing heart failure) or inadequate (causing cyanosis).

~Clinical Features

Symptoms

The clinical presentation depends on the subtype and pulmonary blood flow.

1. Pulmonary Atresia with Intact Ventricular Septum

• Cyanosis soon after birth (within minutes to hours)

• Respiratory distress

• Lethargy or poor feeding

• Failure to thrive

• Episodes of apnea or collapse

Without treatment, death usually occurs within the first days or weeks of life due to severe hypoxemia.

2. Pulmonary Atresia with VSD

• Cyanosis may appear slightly later

• Dyspnea, fatigue, and poor feeding

• If pulmonary flow is excessive, heart failure develops with tachypnea, hepatomegaly, and sweating

• If pulmonary flow is reduced, cyanosis predominates

Physical Examination

• Central cyanosis

• Clubbing (in chronic cases)

• Single S2 (second heart sound)

• Systolic murmur due to VSD or PDA flow

• Hepatomegaly (in congestive cases)

• Weak or absent femoral pulses if PDA closes

~Diagnosis

1. Pulse Oximetry

• Detects low oxygen saturation, typically <80% even with oxygen therapy.

2. Electrocardiogram (ECG)

• Right atrial enlargement

• Left axis deviation (common in PA/IVS)

• Left ventricular hypertrophy (dominant left-sided heart function)

3. Chest X-ray

• Normal or slightly enlarged cardiac silhouette

• Decreased pulmonary vascular markings in reduced flow

• Increased vascularity in excessive flow (PA/VSD with collaterals)

4. Echocardiography (2D + Doppler)

The diagnostic gold standard for pulmonary atresia.
It can identify:

• Absence or imperforate pulmonary valve

• Size and morphology of right ventricle

• Presence of ASD or VSD

• Pulmonary artery anatomy and flow

• PDA or collateral arteries

Echocardiography also assesses tricuspid valve function and coronary artery connections, essential for surgical planning.

5. Cardiac Catheterization and Angiography

Used to:

• Define pulmonary artery anatomy

• Measure oxygen saturations and pressures

• Identify collateral arteries or coronary anomalies

• Evaluate suitability for surgical or interventional procedures

6. Fetal Echocardiography

Detects pulmonary atresia prenatally, allowing planned delivery at a tertiary cardiac center.

~Differential Diagnosis

• Tetralogy of Fallot

• Tricuspid atresia

• Hypoplastic right heart syndrome

• Critical pulmonary stenosis

• Transposition of great arteries with VSD and pulmonary stenosis

~Natural History

Without intervention, pulmonary atresia is usually fatal within days or weeks due to lack of pulmonary blood flow and progressive hypoxemia.

If a PDA remains open, some infants may survive temporarily, but closure of the ductus leads to sudden worsening of cyanosis and circulatory collapse.

In PA/VSD with well-developed collaterals, survival into childhood is possible, though these patients remain cyanotic and develop polycythemia, stroke, or brain abscess if untreated.

~Management

Treatment requires urgent stabilization, followed by staged surgical or interventional repair depending on the anatomy.

1. Initial Medical Management

Goal: Maintain adequate pulmonary blood flow and oxygenation.

• Prostaglandin E₁ (PGE₁) infusion: Keeps the ductus arteriosus open to allow pulmonary perfusion.

• Oxygen therapy: To improve oxygen saturation (though may not be highly effective until surgery).

• Inotropes (dopamine/dobutamine): Support cardiac output if ventricular dysfunction is present.

• Diuretics: Control heart failure in PA/VSD with excessive pulmonary flow.

• Correction of metabolic acidosis and hypoglycemia.

If duct-dependent circulation is identified, prostaglandin therapy is life-saving.

2. Interventional and Surgical Management

Management is tailored to the type of pulmonary atresia.

A. Pulmonary Atresia with Intact Ventricular Septum (PA/IVS)

Goal: Establish reliable pulmonary blood flow and promote right ventricular growth.

i. Catheter-Based Procedures

• Balloon valvotomy or radiofrequency perforation of the pulmonary valve if anatomy is favorable (i.e., thin membrane and well-developed right ventricle).

• Stent placement in PDA to maintain pulmonary flow in selected neonates.

ii. Surgical Options

If catheter-based therapy is not possible:

• Modified Blalock–Taussig shunt: Connects subclavian artery to pulmonary artery to provide blood flow to lungs.

• Right ventricular outflow reconstruction (RV-PA conduit): For larger right ventricles.

• Single-ventricle palliation (Fontan pathway): For severely hypoplastic right ventricle or right ventricle–dependent coronary circulation.

B. Pulmonary Atresia with Ventricular Septal Defect (PA/VSD)

Goal: Re-establish continuity between right ventricle and pulmonary arteries and close the VSD.

i. Palliative Stage

• Aortopulmonary shunt (Blalock–Taussig shunt) to increase pulmonary flow.

• Unifocalization of major aortopulmonary collateral arteries (MAPCAs) to create a unified pulmonary system.

ii. Corrective Surgery

• Complete repair: Closure of VSD and placement of a valved conduit from right ventricle to pulmonary artery.

• Performed when pulmonary arteries are well developed.

iii. Hybrid and Catheter Techniques

• Stenting of collaterals or ductus arteriosus for temporary palliation.

• 3D imaging and mapping to guide complex reconstructions.

~Long-Term Management and Prognosis

Follow-Up

• Lifelong cardiology follow-up is essential.

• Regular echocardiography and MRI to monitor conduit function and right ventricular performance.

• Anticoagulation or aspirin to prevent thromboembolic complications after shunt or Fontan surgery.

• Endocarditis prophylaxis before dental or surgical procedures.

Complications

• Recurrent cyanosis (due to shunt blockage)

• Heart failure

• Arrhythmias

• Thrombosis

• Right ventricular dysfunction

• Re-stenosis of conduits

• Protein-losing enteropathy (in Fontan patients)

Prognosis

With modern surgical techniques:

• Early survival: >85–90%

• 10-year survival: Around 75–80%

• Quality of life significantly improved, with many patients reaching adulthood and leading near-normal lives.

Prognosis depends on:

• Size of right ventricle

• Coronary anatomy

• Pulmonary artery development

• Timely surgical intervention

~Recent Advances

• Fetal intervention: In-utero procedures to open the atretic pulmonary valve (experimental).

• 3D imaging & printing: Help surgeons plan complex reconstructions.

• Biodegradable conduits: Reduce need for reoperations in growing children.

• Heart transplantation: Option for patients with failed palliation or Fontan circulation.

~Prevention and Genetic Counseling

Though prevention is not always possible, certain measures can lower risk:

• Avoid teratogens (alcohol, retinoids, certain drugs).

• Control maternal diabetes.

• Rubella vaccination before pregnancy.

• Prenatal ultrasound and fetal echocardiography for early detection.

• Genetic counseling for families with history of congenital heart disease.

~Conclusion

Pulmonary atresia is a complex congenital heart defect that severely compromises pulmonary blood flow and oxygenation. Prompt diagnosis, medical stabilization, and carefully staged surgical interventions are critical for survival.

Thanks to remarkable progress in pediatric cardiology and surgery, the outlook for children with pulmonary atresia has improved dramatically. Most can now expect to live into adulthood with good functional capacity, though lifelong monitoring remains essential. Continued advances in fetal detection, catheter-based interventions, and innovative surgical techniques promise even better outcomes in the future.