Cognitive Development: From the Glenn to Fontan

Big Picture

Toddlers with HLHS are at elevated risk for neurodevelopmental differences due to a combination of:

• Altered brain development before birth

• Periods of reduced oxygen delivery (especially pre-Fontan)

• Cardiopulmonary bypass and ICU exposures

• Medical stress, hospitalizations, and feeding challenges

Many children show subtle, uneven profiles rather than global intellectual disability.

Key Takeaways

• HLHS toddlers post-Norwood/Glenn often have mild, uneven cognitive profiles

• Language, attention, processing speed, and executive skills are most commonly affected

• Fatigue and oxygenation significantly influence performance

• Early intervention can substantially improve outcomes

• Outcomes are highly individual and not predictive of future intelligence
  

A breakdown by various areas of cognitive development

1. Global Cognitive Development

• Mildly lower average cognitive scores compared with healthy peers (often still within normal range)

• Slower acquisition of new skills, especially under fatigue or illness

• Greater variability day-to-day in attention and learning capacity

Important: Severe intellectual disability is not typical in the absence of major neurological injury.

2. Language Development

Common patterns

• Delayed expressive language (talking) more than receptive language (understanding)

• Smaller vocabulary and shorter sentences

• Slower speech processing speed

Contributing factors

• Prolonged intubation or reduced early vocalization

• Frequent hospitalizations limiting language-rich interaction

• Fatigue limiting sustained speech effort

3. Executive Function (Early Signs)

Even in toddlerhood, early executive skills may show differences:

• Reduced working memory (holding information briefly)

• Difficulty with task switching

• Slower problem-solving

• Less cognitive flexibility during play

These often become more noticeable at preschool age.

4. Attention & Processing Speed

• Shorter attention span

• Easily overwhelmed in noisy or busy environments

• Slower response time to instructions

• Fatigue significantly worsens attention

This is often physiological, not behavioral.

5. Motor–Cognitive Integration

Motor delays (common in HLHS) affect cognition indirectly:

• Delayed crawling/walking → fewer opportunities for exploration-based learning

• Poor endurance limits sustained play

• Fine motor delays impact early problem-solving and play skills

6. Memory & Learning

• Difficulty consolidating new information

• Learning improves with repetition and structure

• Better performance in familiar routines than novel situations

7. Sensory Processing Differences

Some toddlers exhibit:

• Heightened sensitivity to sound, touch, or movement

• Difficulty regulating arousal (over- or under-responsive)

• These can interfere with attention and learning

8. Emotional Regulation & Social Cognition

• Greater emotional reactivity or withdrawal

• Difficulty self-soothing

• Increased reliance on caregivers for regulation

• Social interest is usually intact but may be fatigue-limited

9. Effects Specific to the Pre-Fontan Period

Before Fontan completion:

• Lower oxygen saturation can affect endurance, alertness, and processing speed

• Cognitive performance may fluctuate with hydration, illness, or oxygenation

• Some gains accelerate after Fontan, but not all challenges resolve

10. Strengths Often Observed

Despite risks, many toddlers with HLHS show:

• Strong social engagement

• Good receptive language

• Curiosity and motivation to interact

• Resilience and adaptability in familiar environments

Summary of Glenn Head

Symptoms, Effects, & Toddler Warning Signs

Glenn head refers to symptoms caused by elevated pressure in the superior vena cava after Glenn circulation, leading to venous congestion in the head and upper body.

Common symptoms include:

• Facial or eyelid swelling

• Redness or flushing of the face and head

• Prominent veins in the neck or scalp

• Head pressure or headache

Physiologic effects include:

• Increased venous pressure in the head, neck, and upper chest

• Slower passive blood flow from the upper body to the lungs

• Potential decreases in oxygen saturation if flow is impaired

• Temporary worsening during illness, dehydration, or crying

Symptoms to Look Out for in Toddlers

Because toddlers cannot describe head pressure or headaches, symptoms often appear as behavioral or physical changes, including:

• Increased irritability or inconsolable crying

• Head-holding, rubbing, or frequent touching of the face or scalp

• Resistance to lying flat or sudden preference for being upright

• Puffiness around the eyes, especially after sleep

• Worsening symptoms during crying, straining, or illness

• Fatigue, decreased activity, or reduced play tolerance

• Vomiting without a clear gastrointestinal cause

• Poor sleep or frequent night waking

Clinical Significance

• Glenn-head symptoms are common early after surgery

• New or worsening symptoms months to a year later are less typical

• Persistent or progressive signs in toddlers should prompt cardiac evaluation to rule out increased resistance or obstruction in the Glenn pathway