Figure 5

Ventricular wall composition in amphibians and human with normal and excessively trabeculated left ventricle. (A,B) Transverse section of the ventricular base of an axolotl (A) and a Xenopus frog (B), showing that the ventricle is highly trabecular and the compact wall is extremely thin. It can also be seen that the solitary atrioventricular canal (AVC) is left-sided and the solitary outflow tract (OFT) is right-sided. (C) Transverse section of the human ventricles at gestational week 20. This heart is not much bigger than the Xenopus heart (B), but the compact wall is much thicker and the trabeculations are much fewer and greater in size. (D) Transverse section of a case of fetal human excessive trabeculation at gestational week 20. Compared to the heart shown in (C), the compact wall is thinner and the trabeculations are more numerous, but this heart is still much different from the amphibian hearts (A–B). (E) Transmural histology of a normal left ventricle of an adult human, showing a thick compact wall and a few trabeculations. (F) Transmural histology of a case of left ventricular excessive trabeculation of an adult human. Compared to the heart shown in (E), the compact wall is thinner and the trabeculations are more numerous, but this wall composition is still much different from that of the amphibian hearts (A–B). (G) Measurements of the width of the compact wall (above the horizontal axis) and trabeculations (below the horizontal axis), shown on a logarithmic scale. Letters refer to the images (A–F) on which the measurements were done. (H) Counting of trabeculations per mm² on images (A–F) showing that the amphibians have a 1–2 orders greater number of trabeculations per area. Staining is Masson’s trichrome in (A), picro-sirius red in (B, E and F), and hematoxylin–eosin in (C and D). The sections shown in (C,D) were part of the data published in²⁷.