Can atrial septal defects (ASDs) close naturally?

Natural Closure of Atrial Septal Defects

Small ASDs (<5-6 mm) have a high likelihood of spontaneous closure, particularly in infants and young children, while defects larger than 8-10 mm rarely close spontaneously and typically require intervention. 1, 2, 3

Size-Based Prediction of Spontaneous Closure

Very Small Defects (≤5 mm)

• ASDs measuring 4-5 mm close spontaneously in approximately 80-90% of cases when diagnosed in infancy or early childhood 2, 3
• The American College of Cardiology notes that defects less than 5 mm without evidence of RV volume overload do not impact natural history and may not require closure unless associated with paradoxical embolism 4, 1
• In one series, 89% of 4 mm defects closed spontaneously or decreased in size 3

Medium Defects (6-9 mm)

• Defects measuring 6-9 mm show intermediate closure rates of approximately 16-79%, with higher rates in younger patients 2, 3
• These defects may regress in size in infants and children (9.5% of infants, 3.7% of children showed regression) 2
• The likelihood of spontaneous closure decreases significantly as defect size increases within this range 3

Large Defects (>10 mm)

• ASDs larger than 10 mm have minimal chance of spontaneous closure and typically require surgical or device closure 1, 2
• In one study, only 1 of 24 defects larger than 8 mm closed spontaneously, while 91% required surgical closure 3
• No spontaneous closure was observed in adolescents or adults with defects exceeding 10 mm 2

Critical Age-Related Factors

Infants and Young Children

• Spontaneous closure is most likely when the defect is diagnosed in the first year of life 2, 5
• Among infants with small defects, 81% experienced spontaneous closure 2
• The window for spontaneous closure extends through early childhood but diminishes significantly after age 5 years 2, 3

Adolescents and Adults

• No spontaneous closure was detected in adolescents or adults in natural history studies 2
• Larger defects may actually enlarge over time in 29% of cases, particularly those initially measuring ≥9 mm 5
• The American Heart Association notes that larger defects with RV volume overload typically only cause symptoms in the third decade of life, but closure is indicated to prevent long-term complications regardless of symptoms 4

Clinical Implications for Management

When to Observe vs. Intervene

• Small defects (≤5 mm) without RV volume overload warrant observation with serial echocardiography, as spontaneous closure is likely 1, 2
• Defects 6-9 mm require close monitoring as they may enlarge, remain stable, or occasionally close 2, 5
• Defects >10 mm should proceed to closure planning, as spontaneous resolution is extremely unlikely 1, 2

Key Pitfall to Avoid

• Do not delay closure based solely on absence of symptoms, as symptoms lag behind objective cardiopulmonary dysfunction and cannot guide therapy 1
• The American College of Cardiology emphasizes that 72% of patients in one series ultimately needed surgical repair or transcatheter closure 2
• Nearly 25% of patients with unoperated ASDs die before age 27, and 90% by age 60, making timely closure essential when indicated 1

Monitoring Strategy

• Serial echocardiographic evaluation is essential for medium-sized defects to detect enlargement, which occurs in approximately 25-29% of cases 5
• The presence of right atrial and right ventricular enlargement indicates hemodynamic significance and warrants closure regardless of defect size or symptoms 1, 6