Disproportionate ventricular septal thickening in the developing normal human heart

Area of Science:

• Cardiovascular Development
• Cardiac Anatomy
• Developmental Biology

Background:

• Hypertrophic cardiomyopathy is characterized by thickened ventricular septum and disorganized muscle cells.
• Understanding early heart development may elucidate hypertrophic cardiomyopathy pathogenesis.

Purpose of the Study:

• To investigate ventricular wall thickness and septal-free wall ratios in normal human embryonic and fetal hearts.
• To compare these ratios with those in newborns to understand developmental changes.

Main Methods:

• Morphologic observations of 151 normal human embryos, fetuses, and term infants.
• Measurement of ventricular septal and left ventricular free wall thicknesses.
• Calculation of the septal-free wall ratio across different developmental stages.

Main Results:

• Disproportionate septal thickening (ratio ≥ 1.3) was observed in 94% of embryos/young fetuses and 65% of older fetuses.
• This disproportion decreased significantly with age, approaching 1.0 in newborns (12% of infants >2 weeks).
• Free wall thickness increased at a greater rate than septal thickness postnatally, normalizing the ratio.

Conclusions:

• Disproportionate septal thickening is a normal feature of early human heart development.
• The resolving nature of this thickening suggests it is not indicative of cellular disorganization seen in hypertrophic cardiomyopathy.
• These findings provide a baseline for understanding normal cardiac morphogenesis and differentiating it from pathological conditions.