What is the natural timing of closure for atrial septal defects (ASD)?

Natural Timing of Closure of Atrial Septal Defects

Spontaneous Closure Rates by Defect Size and Age

Small ASDs (<5-6 mm) diagnosed in infancy have an 80-100% chance of spontaneous closure by 12-18 months of age, while defects ≥8-10 mm rarely close spontaneously and typically require intervention. 1, 2

Infants Diagnosed in First Year of Life

• Defects <3 mm: 100% spontaneous closure by 18 months of age 1
• Defects 3-5 mm: 87% spontaneous closure, typically by 12 months 1
• Defects 5-8 mm: 80% spontaneous closure, typically by 15 months 1, 2
• Defects ≥8 mm: Minimal chance of spontaneous closure; no closures observed during average 417-day follow-up 1

Children and Adolescents

• Defects 4-6 mm: 79-89% will close spontaneously or decrease in size 2
• Defects 7-8 mm: Only 16.6% close spontaneously; 37.5% require surgical closure 2
• Defects >8-10 mm: <5% spontaneous closure rate; 91% require surgical or device closure 3, 2
• No spontaneous closure occurs in adolescents or adults regardless of defect size 3

Critical Timing Considerations

Age at Diagnosis Determines Natural History

The likelihood of spontaneous closure is inversely related to both defect size and age at diagnosis 3. Defects diagnosed after infancy have progressively lower rates of spontaneous closure, and no spontaneous closures occur after adolescence. 3

Dynamic Nature of Defects

ASDs can enlarge over time in 29% of cases, particularly larger defects (≥9 mm), making serial echocardiographic surveillance essential. 4 This enlargement pattern is clinically important in the transcatheter closure era, as defects initially suitable for device closure may grow beyond device size limitations 4.

Recommended Surveillance Strategy

For Small Defects (≤5 mm)

• Infants with defects <3 mm do not require follow-up beyond 18 months, as 100% will close 1
• Defects 3-5 mm should be evaluated at 12 months when >80% will be closed 1
• Defects 5-8 mm require evaluation at 15 months 1

For Moderate to Large Defects (>8 mm)

Defects ≥8-10 mm should be considered for elective closure rather than prolonged observation, as spontaneous closure is extremely unlikely and complications develop with age. 3, 1, 2 The ACC/AHA guidelines emphasize that larger defects with RV volume overload typically cause symptoms in the third decade of life, but closure is indicated before symptoms develop to prevent long-term complications 5.

Clinical Implications for Intervention Timing

Optimal Age for Closure

Outcome is best with repair before age 25 years, as surgery performed after this age results in reduced survival compared to age-matched controls. 5, 6 The ESC guidelines note that ASD closure after age 40 does not affect the frequency of arrhythmia development during follow-up, though patients still benefit regarding morbidity 5.

Mortality Without Closure

Nearly 25% of patients with unoperated ASDs die before age 27, and 90% by age 60, making timely closure essential even in asymptomatic patients. 6 This underscores that delaying closure based on absence of symptoms is a critical pitfall, as symptoms lag behind objective cardiopulmonary dysfunction. 6

Key Predictive Factors

The two most important predictors of spontaneous closure are: 3

1. Defect diameter at diagnosis: Smaller defects (<6 mm) close spontaneously in >80% of cases
2. Age at diagnosis: Infants have highest closure rates; no spontaneous closure after adolescence

Gender Considerations

The classic female predominance (60% female) is observed only for defects >5 mm, suggesting that very small defects may represent normal anatomic variants rather than true cardiac malformations 1.

Common Pitfalls to Avoid

• Do not assume all small ASDs will close: 13% of 3-5 mm defects and 20% of 5-8 mm defects persist beyond expected closure timeframes 1
• Do not delay intervention for large defects (>10 mm) awaiting spontaneous closure: These have <5% closure rates and 72% ultimately require intervention 3
• Do not discontinue surveillance after initial decrease in size: 29% of defects enlarge over time, particularly those initially ≥9 mm 4
• Do not wait for symptoms to develop before considering closure: Optimal outcomes require repair before age 25, well before most patients become symptomatic 5, 6