What is a small Atrial Septal Defect (ASD)/Patent Foramen Ovale (PFO)?

Understanding Small Atrial Septal Defect (ASD) and Patent Foramen Ovale (PFO)

A small ASD or PFO is a hole or tunnel-like opening in the wall between the heart's upper chambers (atria) that allows blood to flow between them, but is typically too small to cause significant heart problems in most people.

What is the Difference Between ASD and PFO?

Patent Foramen Ovale (PFO)

• Definition: A PFO is not a true defect but rather a tunnel-like communication between the septum primum and septum secundum located in the anterosuperior portion of the atrial septum 1
• Prevalence: Found in approximately 25-30% of adults 2
• Origin: A normal part of fetal circulation that typically closes shortly after birth but remains open in some people
• Size: Usually small, functioning like a flap valve

Small Atrial Septal Defect (ASD)

• Definition: A true deficiency of atrial septal tissue 1
• Types:
  • Secundum ASD (most common, 75% of cases) - located within the fossa ovalis 1
  • Primum ASD (15-20%)
  • Sinus venosus ASD (5-10%)
  • Coronary sinus septal defect (less than 1%) 1
• Size classification: Small ASDs are generally defined as less than 5mm in diameter 1

How They Affect Your Heart

Small ASD

• Blood flow: Creates a small left-to-right shunt (blood flows from the left atrium to the right atrium)
• Impact: Small ASDs (less than 5mm) with no evidence of right ventricular volume overload typically do not impact the natural history of the individual 1
• Symptoms: Usually asymptomatic in childhood and early adulthood

PFO

• Blood flow: Normally no significant shunting occurs, but during certain conditions (like straining or coughing) that increase right atrial pressure, blood can flow from right to left atrium
• Impact: Usually has no hemodynamic significance
• Potential concern: May allow paradoxical embolism (blood clots passing from venous to arterial circulation) 1

Potential Health Implications

Small ASD

• Long-term concerns: Larger ASDs (not small ones) may eventually cause:
  • Right heart enlargement
  • Atrial arrhythmias (typically in third decade of life or later)
  • Reduced exercise tolerance
  • Tricuspid regurgitation 1
• Rare complications: Pulmonary vascular disease may develop in 5-10% of affected individuals (mainly females) with larger defects 1

PFO

• Main concern: Potential risk for paradoxical embolism, which could lead to cryptogenic stroke (stroke with no identifiable cause) 1
• Risk factors: The risk may be higher with:
  • Larger PFO size
  • Greater magnitude of right-to-left shunt
  • Coexistence of atrial septal aneurysm (a bulging of the septum) 1

Diagnosis

• Echocardiography: The primary tool for diagnosis
  • Transthoracic echocardiography (TTE): First-line imaging
  • Transesophageal echocardiography (TEE): More detailed assessment
  • 3D echocardiography: Provides enhanced visualization 1
• Bubble study: Injection of agitated saline to detect right-to-left shunting

When to Be Concerned

• For small ASD: Generally no intervention needed if less than 5mm and no right ventricular volume overload 1
• For PFO: Most people with PFO never have any problems, but it may be significant if:
  • You've had a stroke with no other identifiable cause (cryptogenic stroke)
  • You have recurrent, unexplained neurological symptoms

Treatment Options

• Small ASD:

  • Usually requires no treatment if less than 5mm with no right ventricular volume overload 1
  • Monitoring with periodic echocardiography may be recommended

• PFO:

  • Most PFOs don't require treatment
  • Closure may be considered in cases of documented systemic embolism probably caused by paradoxical embolism 1, 3
  • The European Society of Cardiology suggests that PFO closure should only be considered in cases of documented systemic embolism probably caused by paradoxical embolism 3

Important Considerations

• The presence of a small ASD or PFO alone is not a reason for activity restrictions
• Most people with these conditions lead normal, active lives without complications
• If you have a diagnosed small ASD or PFO, discuss with your doctor whether any follow-up is needed
• Be aware of symptoms that might indicate complications (unexplained shortness of breath, palpitations, or neurological symptoms)

Conclusion

Small ASDs and PFOs are common findings that usually don't cause symptoms or require treatment. Understanding the difference between these conditions and knowing when they might become significant can help you have informed discussions with your healthcare provider.