Which Phenotypes Should We Include in the Hypoplastic Left Heart Syndrome?

Area of Science:

• Pediatric Cardiology
• Congenital Heart Surgery
• Developmental Biology

Background:

• A recent special issue on hypoplastic left heart syndrome (HLHS) lacked focus on ventricular septal integrity for phenotype distinction.
• Differentiating HLHS from related anomalies requires clear criteria for classifying specific cardiac malformations.

Purpose of the Study:

• To propose the integrity of the ventricular septum as a primary criterion for distinguishing HLHS phenotypes.
• To re-evaluate the classification of HLHS and related anomalies based on developmental timing.

Main Methods:

• Review of existing evidence on HLHS and related congenital heart defects.
• Analysis of the role of ventricular septal integrity in cardiac development.
• Comparative evaluation of different HLHS phenotypes based on proposed criteria.

Main Results:

• The integrity of the ventricular septum serves as a crucial distinguishing feature between HLHS and related anomalies.
• Phenotypes within HLHS can be categorized by the timing of left ventricular growth arrest relative to cardiac development, post-septum closure.
• Specific recognized combinations include aortic/mitral atresia, mitral stenosis with aortic atresia, and combined mitral/aortic stenosis.

Conclusions:

• Classifying HLHS based on ventricular septal integrity and developmental timing offers a refined understanding of these complex congenital heart defects.
• This approach aids in recognizing the spectrum of lesions, including the hypoplastic left heart complex, and their origins as acquired fetal conditions.