3D reconstruction of the AV junction
A more direct view of the relationships among different structures could
be achieved following the 3D reconstruction of the AV junction. In
summary, atrial and ventricular tissues (Cx43-positive and HCN4-negative
tissues), nodal tissue (Cx43-negative; HCN4-positive; Cx40-negative and
strongly Cx45-positive
tissue),
PB tissue (Cx43-negative; HCN4-positive; Cx40-positive and strongly
Cx45-positive tissue) and connective tissue (Masson’s trichrome-stained
tissue, blue) were present at the AV junction. Figure 4A summarizes the
distribution of cell types in all 80 levels that were studied (images
are prior to alignment), wherein only the tract of the nodal tissue and
nearby tissue is shown. The nodal tissue includes the CN, inferior
extension and RN (bright yellow), Cx40-positive tissue of the PB (red),
atrial and ventricular muscle (sandy), and connective tissue (light
blue), as shown in Figure 4 (left). These images of serial sections
showed changing trends in the distribution, location and volume of cell
types at the AV junction. The sections shown in Figure 4 (left) were
used to generate a 3D anatomical model of the AVN.
Various views of the model are shown in Figure 4 (right) (atria and
ventricles were removed to highlight junctional tissues). Based on the
patterns of connexin and HCN4 expression, we propose that the anterior
extension, CN and inferior extension contain the same cell types. The
positional and volumetric relationships among them are shown in Figure 4
(right). The inferior extension gradually decreased in volume moving
away from the CN, with no obvious boundary with the CN. However, the
shape of the RN was similar to a shuttle. Its connection with the CN was
narrow. It expanded, with an increasing volume moving away from the CN,
which then decreased again at the anterior septum. The volume of the PB
decreased as the level increased and disappeared into the CN (red part
of the model).