Pulmonary Atresia without VSD

Introduction

Pulmonary Atresia without Ventricular Septal Defect (VSD) is a severe congenital heart disease characterized by the absence or fusion of the pulmonary valve, preventing blood flow from the right ventricle to the lungs. Neonatal survival depends entirely on the patency of the ductus arteriosus or the presence of major aortopulmonary collateral arteries (MAPCAs), which supply pulmonary blood flow.
Pulmonary Atresia can manifest in two main forms: **Pulmonary Atresia without VSD**, the focus of this discussion, and Pulmonary Atresia with Intact Ventricular Septum, previously covered.
Although their names may seem semantically similar, these are distinct conditions:

• Pulmonary Atresia without VSD: absence of the ventricular septal defect, with a hypoplastic right ventricle and pulmonary blood flow sustained by aortopulmonary collateral arteries or the ductus arteriosus.
• Pulmonary Atresia with Intact Ventricular Septum: the ventricular septum remains intact, the right ventricle is more developed, and pulmonary blood flow depends exclusively on the ductus arteriosus.

This distinction is crucial as treatment strategies and prognosis vary between the two conditions.

Anatomy and Pathophysiology

Pulmonary atresia without ventricular septal defect is characterized by:

• A completely atretic pulmonary valve, preventing normal blood flow from the right ventricle to the lungs.
• A hypoplastic right ventricle, secondary to reduced function and underdevelopment due to the lack of pressure load.
• Pulmonary blood flow dependent on a patent ductus arteriosus (PDA) or the presence of major aortopulmonary collateral arteries (MAPCAs), compensating for the absence of a functional pulmonary artery.

Systemic oxygenation is severely compromised, with progressive hypoxemia if left untreated.

Epidemiology

Pulmonary Atresia without VSD is a rare condition, with an estimated incidence of approximately 1 in 20,000 live births. It is frequently associated with genetic anomalies, particularly DiGeorge syndrome (22q11.2 deletion), which can lead to immune deficiencies, hypocalcemia, and craniofacial abnormalities.

Signs and Symptoms

The clinical presentation is early and manifests within the first hours of life with:

• Severe cyanosis, often evident immediately after birth.
• Respiratory distress and progressive tachypnea.
• Fatigue and feeding difficulties, secondary to systemic hypoxemia.
• Heart murmur, usually present due to blood flow through collateral circulations or shunts.

Without immediate intervention, the condition is rapidly fatal within the first few days of life.

Diagnosis

Pulmonary Atresia without VSD can be identified prenatally through fetal echocardiography. After birth, the diagnosis is confirmed through:

• Echocardiography: reveals the absence of the pulmonary valve and the presence of compensatory blood flow.
• Cardiac catheterization: crucial for assessing the anatomy of the pulmonary collateral circulation.
• Cardiac magnetic resonance imaging (MRI): useful for detailed mapping of pulmonary vessels.

Treatment

Treatment is exclusively surgical and depends on the morphology of the pulmonary circulation:

• Neonatal management: administration of prostaglandins (PGE1) to maintain ductal patency.
• Systemic-to-pulmonary shunt: connection between the aorta and the pulmonary arteries to ensure adequate blood flow.
• Unifocalization: in patients with aortopulmonary collateral arteries (MAPCAs), to create a more uniform vascular system.
• Definitive repair: may include the placement of a ventricular-pulmonary conduit to restore a biventricular circulation.

In the most severe cases, where cardiopulmonary function is significantly compromised, heart-lung transplantation may be the only viable option.

Prognosis

Without treatment, survival is extremely limited. With surgery, quality of life can improve significantly, though many patients require additional interventions to optimize long-term cardiopulmonary function.

References
1. Tweddell J.S. et al. Pulmonary Atresia Without VSD: Surgical and Long-Term Outcomes. Ann Thorac Surg. 2020;109(5):1123-1136.
2. Jacobs M.L. et al. Reconstructive Strategies in Pulmonary Atresia Without VSD. Circulation. 2019;140(9):789-802.
3. Freedom R.M. et al. Pulmonary Atresia: Natural History and Management. J Am Coll Cardiol. 2018;136(4):1205-1214.
4. Graziano J.N. et al. Outcomes of Pulmonary Atresia Without VSD. Pediatr Cardiol. 2021;42(3):511-523.
5. Brigham K.L. et al. Advancements in Surgical Treatment of Pulmonary Atresia. J Thorac Cardiovasc Surg. 2019;158(6):1250-1262.
6. Bove E.L. et al. Long-Term Management Strategies for Pulmonary Atresia. J Am Coll Cardiol. 2020;145(2):205-218.