What is the pediatric Norwood procedure for hypoplastic left heart syndrome (HLHS)?

The Norwood Procedure for Hypoplastic Left Heart Syndrome (HLHS)

The Norwood procedure is the first stage of a three-stage surgical palliation for hypoplastic left heart syndrome (HLHS), a fatal condition that would result in 90% mortality within the first month of life without intervention. 1

Overview and Purpose

The Norwood procedure, first described in 1981, is designed to achieve four critical objectives:

• Provide an unobstructed systemic outflow tract 1
• Create an unrestrictive inter-atrial communication 1
• Establish a controlled source of pulmonary blood flow 1
• Ensure a reliable source of coronary blood flow 1

Surgical Technique

The traditional Norwood procedure consists of several key components:

• Anastomosis of the main pulmonary artery to the hypoplastic aorta to create a neo-aorta 1
• Creation of a systemic-to-pulmonary artery shunt (modified Blalock-Taussig shunt) or a right ventricle-to-pulmonary artery conduit (Sano modification) 1
• Atrial septectomy to ensure unrestricted blood flow between the atria 1
• Reconstruction of the aortic arch to provide unobstructed systemic blood flow 1

Sano Modification

The Sano modification of the Norwood procedure, described in 2000, uses a right ventricle-to-pulmonary artery conduit instead of the traditional systemic-to-pulmonary artery shunt. This modification aims to improve hemodynamic stability by eliminating the diastolic "steal" phenomenon that can occur with the traditional shunt. 1

Outcomes and Survival

• Overall survival after the Norwood procedure has improved significantly over time but appears to have plateaued in recent years 2
• Historical in-hospital mortality decreased from 40.4% in the 1980s to approximately 15.7% in recent years 2
• Risk factors for mortality include:
  • Anomalous pulmonary venous drainage 2
  • Moderate to severe atrioventricular valve regurgitation 2
  • Lower birth weight and gestational age 2
  • Genetic anomalies 2
  • Prolonged cardiopulmonary bypass time 3

Staged Palliation Approach

The Norwood procedure is the first stage in a three-stage approach:

1. Stage I (Norwood): Performed in the neonatal period to establish systemic outflow and controlled pulmonary blood flow 1
2. Stage II (Bidirectional Glenn/Hemi-Fontan): Performed at 3-6 months of age to direct superior vena cava blood directly to the pulmonary arteries 1
3. Stage III (Fontan completion): Performed at 2-5 years of age to direct inferior vena cava blood to the pulmonary circulation, completing the separation of systemic and pulmonary circulations 1

Hybrid Alternative Approach

A hybrid approach has emerged as an alternative to the traditional Norwood procedure, particularly for high-risk patients:

• Combines surgical and interventional catheterization techniques 1
• Consists of:
  • Surgical placement of bilateral pulmonary artery bands 1
  • PDA stent implantation 1
  • Creation of an unrestrictive atrial communication 1
• Performed without cardiopulmonary bypass 1
• May be particularly beneficial for:
  • High-risk surgical candidates 1
  • Patients with ventricular dysfunction 4
  • Patients with multisystem organ failure 4
  • As a bridge to heart transplantation 1

Complications and Risks

• Potential complications of the Norwood procedure include:

  • Coronary insufficiency 1
  • Shunt thrombosis or stenosis 1
  • Pulmonary overcirculation or undercirculation 1
  • Ventricular dysfunction 4
  • Atrioventricular valve regurgitation 2

• Complications specific to the hybrid approach include:

  • Stent embolization 1
  • Retrograde coarctation 1
  • Proximal stenosis of uncovered ductus 1
  • Pulmonary artery distortion from banding 1

Long-term Considerations

• Neurodevelopmental outcomes remain a concern, with multiple studies showing abnormal IQ and neurodevelopmental testing after the Norwood procedure 1
• Regular follow-up with imaging (echocardiography, cardiac MRI) is essential to monitor ventricular function and detect potential complications 1
• Cardiac catheterization may be needed to assess hemodynamics and pulmonary vascular resistance during the staged palliation process 5

Contraindications for Hybrid Approach

• Significant retrograde aortic arch obstruction with a fully open PDA is a contraindication to the hybrid approach due to potential acute obstruction to coronary flow 1, 4

The Norwood procedure represents a milestone in congenital cardiac surgery, transforming HLHS from a uniformly fatal condition to one with a reasonable chance of survival through childhood 6.