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Disproportionate ventricular septal thickening in the developing normal human heart
Insights
Normal fetal heart development shows disproportionate septal thickening, which resolves after birth. This finding is crucial for understanding hypertrophic cardiomyopathy origins.
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.
Abstract:
A disproportionately thickened ventricular septum containing numerous disorganized cardiac muscle cells is the most characteristic anatomic feature of hypertrophic cardiomyopathy. Since information concerning ventricular wall thicknesses and cellular arrangement in the developing heart may be pertinent to understanding the genesis of hypertrophic cardiomyopathy, morphologic observations were made in 151 normal human embryos, fetuses and term infants. Disproportionate ventricular septal thickening (septal-free wall ratio greater than or equal to 1.3) was present in 94% of embryos and young fetuses; in over one-third disproportionate thickening was particularly pronounced (septal-free ratio greater than or equal to 2.0). Disproportionate septal thickening was also present in 65% of older fetuses, but in only 12% of infants over two weeks of age. Septal-free wall ratio decreased in a curvilinear fashion with increasing age and apporixmated unity in the newborn. This phenomenon occurred because, while both ventricular septal and left ventricular free wall thicknesses increased directly with age, free wall thickness increased at a greater rate than septal thickness, particularly after birth. Marked cellular disorganization in the septum was not a feature of the hearts studied.