Can a positive outcome from a 24-32 week echo showing no longer Hypoplastic Left Heart Syndrome (HLHS) improve further at the 37-week echo?

Fetal Echocardiography Follow-up in Resolving Hypoplastic Left Heart Syndrome

Yes, a positive outcome at 24-32 weeks showing resolution of Hypoplastic Left Heart Syndrome (HLHS) can further improve at the 37-week echo, with continued cardiac development and maturation potentially showing additional positive changes.

Understanding Fetal Cardiac Development

Fetal cardiac development is dynamic and continues throughout pregnancy. When HLHS appears to be resolving between 24-32 weeks, this represents a significant positive change in the developmental trajectory of the fetal heart.

• The American Heart Association guidelines emphasize that ongoing monitoring of complex congenital heart disease is crucial for proper planning and management 1
• Fetal echocardiography is highly accurate when performed by skilled operators and is the standard method for detecting and monitoring fetal cardiovascular disease 2

What to Expect at 37-Week Echo

The 37-week echocardiogram should evaluate:

1. Ventricular size and growth:

   • Further growth of the previously hypoplastic left ventricle
   • Improved chamber dimensions compared to earlier scans

2. Ventricular function:

   • Ventricular wall fractional shortening (should be >28% for normal function) 1
   • Overall contractility and cardiac output

3. Valve development:

   • Mitral and aortic valve growth and function
   • Resolution or improvement of any previously noted valve regurgitation 1

4. Blood flow patterns:

   • Improved antegrade flow through the left heart
   • Normal diastolic function via atrioventricular inflow patterns
   • Normal ductus venosus flow patterns 1

Significance of Continued Improvement

The continued improvement at 37 weeks would be significant for:

• Postnatal outcomes: Improved cardiac structure and function correlate with better neonatal outcomes
• Surgical planning: May reduce or eliminate the need for staged surgical palliation that is typically required for HLHS 3
• Long-term prognosis: Better developed left heart structures at birth generally correlate with improved long-term outcomes

Monitoring Recommendations

For optimal assessment of continued improvement:

• Complete fetal echocardiography at 37 weeks should be performed by specialists with expertise in fetal cardiac imaging 2
• The evaluation should include comprehensive assessment of all cardiac structures and function 2
• Doppler studies should assess blood flow patterns through all chambers and vessels 2

Clinical Implications

If continued improvement is seen at 37 weeks:

• Delivery planning may be adjusted to reflect the improved cardiac status
• Postnatal management may shift from immediate intervention to careful observation
• Long-term follow-up would still be required, as some cardiac issues may only become apparent after birth

Potential Pitfalls

• False reassurance: Even with apparent resolution of HLHS, subtle abnormalities may persist that could impact postnatal cardiac function
• Evolution of defects: Some cardiac defects can evolve or progress even after appearing to resolve 4
• Technical limitations: Image quality at later gestational ages may be affected by fetal position and maternal factors

Conclusion

The positive changes noted between 24-32 weeks can indeed continue to improve at 37 weeks, potentially resulting in a more favorable cardiac structure and function at birth. However, comprehensive postnatal cardiac evaluation remains essential to confirm the resolution of HLHS and identify any residual abnormalities that may require intervention.