How are atrial septal defects (ASDs) classified by size in pediatric (peds) patients?

Atrial Septal Defect Size Classification in Pediatric Patients

Atrial septal defects (ASDs) in pediatric patients are primarily classified as small (≤2.0 cm) or moderate to large (>2.0 cm), with this classification based on hemodynamic significance rather than absolute measurements alone. 1

Standard Classification System

According to the American College of Cardiology/American Heart Association/American Society of Echocardiography guidelines, ASDs are classified as:

• Small: ASDs that are likely to be hemodynamically insignificant
• Moderate to large: ASDs that are likely to be hemodynamically significant
• Present, but unable to characterize further: When size cannot be adequately determined 1

Size-Specific Criteria

The European Society of Cardiology provides more specific size measurements:

• Small to moderate: ≤2.0 cm in diameter
• Large: >2.0 cm in diameter 1, 2

For infants and younger children, some studies use more age-appropriate size classifications:

• In infants:

  • Small: ≤5 mm
  • Medium: 6-9 mm
  • Large: >9 mm 3

• In children and adolescents:

  • Small: ≤10 mm
  • Medium: 10-20 mm
  • Large: >20 mm 3

Clinical Significance of Size Classification

The size classification directly correlates with clinical outcomes and management decisions:

• Small defects (<6 mm): High likelihood of spontaneous closure (79-89%) 4, 3
• Medium defects (6-9 mm): May regress in size but have lower spontaneous closure rates
• Large defects (>8-10 mm): Rarely close spontaneously and typically require intervention 4, 3

Hemodynamic Impact

The classification system prioritizes hemodynamic significance over absolute size:

• Hemodynamically insignificant (small): Minimal right heart volume overload, no pulmonary hypertension
• Hemodynamically significant (moderate to large): Right heart enlargement, increased pulmonary blood flow, risk of pulmonary hypertension 1, 2

Risk Stratification

The size classification helps predict complications:

• Small defects: Only 3% develop pulmonary hypertension
• Large defects: Up to 50% develop pulmonary arterial hypertension with pulmonary vascular disease 1, 2

Management Implications

The size classification directly guides treatment decisions:

• Small ASDs (<6 mm): Often managed conservatively with monitoring for spontaneous closure
• Medium ASDs (6-10 mm): May require closure if no regression is observed
• Large ASDs (>10 mm): Usually require surgical or transcatheter closure 2, 3

Measurement Technique

Accurate measurement is crucial and typically performed using:

• Transthoracic echocardiography from subxyphoid long and short axis views
• Transesophageal echocardiography when better visualization is needed 4, 5

The classification of ASDs by size in pediatric patients is essential for predicting clinical outcomes and determining appropriate management strategies, with the primary distinction being between hemodynamically significant and insignificant defects.