# Truncus Arteriosus and Pulmonary Atresia

> Truncus arteriosus and pulmonary atresia for NEET-PG Paediatrics covering single arterial trunk types, DiGeorge association and duct-dependent pulmonary flow.

- Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/truncus-arteriosus-and-pulmonary-atresia
- Exam / course: NEET-PG · Subject: Paediatrics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Nadas' Pediatric Cardiology; Ghai Essential Pediatrics
- How to cite: "Truncus Arteriosus and Pulmonary Atresia", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/truncus-arteriosus-and-pulmonary-atresia

## Direct answer

Truncus arteriosus is a single arterial trunk arising from both ventricles through a ventricular septal defect, supplying the systemic, pulmonary and coronary circulations. In pulmonary atresia the pulmonary valve is closed or absent, so pulmonary blood flow depends on the ductus arteriosus or on collateral arteries. Early prostaglandin support is the key neonatal measure when the duct supplies the lungs.

## What you must remember

- **Single trunk:** one arterial trunk overrides a ventricular septal defect and gives rise to the pulmonary, systemic and coronary arteries.
- **Collett and Edwards types:** type I has a short main pulmonary artery from the trunk, type II has separate pulmonary arteries from the posterior wall, type III has them from the lateral walls, and type IV lacks pulmonary arteries.
- **DiGeorge association:** truncus arteriosus is strongly linked to 22q11.2 deletion, so hypocalcaemia and immune deficiency are looked for.
- **Early physiology:** high pulmonary flow causes heart failure in the first weeks, with later pulmonary vascular disease if untreated.
- **Truncal valve:** regurgitation or stenosis of the common valve is frequent and influences the timing of surgery.
- **Repair:** early complete repair uses a right ventricle to pulmonary artery conduit with VSD closure, ideally in infancy.
- **Pulmonary atresia with intact septum:** neonatal cyanosis with a closed valve and a small right ventricle, kept alive by the ductus.
- **Pulmonary atresia with VSD:** often with major aortopulmonary collateral arteries supplying the lungs.

## Following pulmonary blood flow through each lesion

Both lesions ask where the lungs get their blood. The steps below trace that flow from the trunk or the atresia to definitive treatment.

1. **Trunk origin:** in truncus arteriosus, one trunk takes blood from both ventricles across the VSD, so systemic and pulmonary flows mix.
2. **Pulmonary branch origin:** the Collett and Edwards type depends on where the pulmonary arteries arise, which guides the surgical technique.
3. **Early flow:** high pulmonary flow causes heart failure in the first weeks, with tachypnoea and poor feeding.
4. **Repair:** a conduit from the right ventricle to the pulmonary arteries, with VSD closure, is performed in infancy once the child is stable.
5. **Atresia with intact septum:** the right ventricle is small and pulmonary blood comes only through the ductus.
6. **Duct maintenance:** prostaglandin E1 keeps the duct open until a balloon or surgical procedure opens the pulmonary outflow. Closing the duct early in these children can be fatal.

## Where the exam tries to catch you

Truncal and atretic lesions are tested on physiology and on the drug that keeps the duct open. Watch for these traps.

- **Trap:** Assuming truncus arteriosus is an isolated VSD with a normal aorta. — **Correct:** The single trunk supplies the coronary, pulmonary and systemic circuits, so the lesion is a separate arterial origin.
- **Trap:** Stopping prostaglandin in pulmonary atresia because the child looks better. — **Correct:** Pulmonary blood flow depends on the duct, so the infusion continues until a definitive procedure is done.
- **Trap:** Linking truncus only to cyanotic presentations. — **Correct:** Early truncus often presents with heart failure from high pulmonary flow rather than cyanosis.

## Frequently asked questions

### What is the commonest type of truncus arteriosus?

Type I truncus arteriosus is commonly described as the commonest form, in which a short main pulmonary artery arises from the trunk and then divides into the right and left pulmonary arteries. Its classic features are a large VSD, a single trunk and a common truncal valve.

### Why is truncus arteriosus linked to DiGeorge syndrome?

Truncus arteriosus is a conotruncal defect strongly associated with 22q11.2 deletion, the genetic basis of DiGeorge syndrome. Affected children need checks for hypocalcaemia from parathyroid hypoplasia and for immunodeficiency from thymic hypoplasia.

### Why does pulmonary atresia with intact septum need prostaglandin?

In pulmonary atresia with intact ventricular septum, the pulmonary valve is closed and the right ventricle is often small, so pulmonary blood flow depends on a patent ductus arteriosus. Prostaglandin E1 keeps that duct open until a surgical or balloon procedure can open the pulmonary outflow.

### How does pulmonary atresia with VSD differ from the intact septum form?

Pulmonary atresia with ventricular septal defect has a large VSD and a closed or absent pulmonary valve, and pulmonary blood flow often comes from major aortopulmonary collateral arteries. Surgical correction aims to connect the right ventricle to the pulmonary arteries or to provide a shunt, depending on anatomy.