Figure legends
Figure 1. (A) Schematic of a heart with a window cut into the
right atrium to visualize the location of the atrioventricular node
(AVN). (B) Image of the AVN preparation used for constructing the model,
the location of sections and the angle of the knife.
Figure 2. The 13th, 39th,
and 79th groups of serial sections are shown. (A)
Masson’s trichrome-stained section. (B) AChE staining: AChE expression
was largely positive around the tricuspid ring and dispersed in
distribution (arrow). (C) Cx43 (green) and HCN4 (red) double-staining
showed reciprocal Cx43 and HCN4 expression. (D) Cx40 (green) and Cx45
(red) double-label staining showed abundant Cx45 expression in the
penetrating bundle (PB) tissue and areas along the atrial side where
Cx43 expression was absent. Cx40 was expressed only in the PB tissue.
(E) Masson’s trichrome-stained section. (F) AChE staining: Rusty-colored
tissues highlighted a linear connection with the atrioventricular node
(AVN) from the atrial side. (G) Cx43 (green) and HCN4 (red)
double-staining revealed a correlation with AChE staining. (H) Cx40
(green) and Cx45 (red) double-staining showed abundant Cx45 expression
in areas without Cx43 expression. PB tissue showed a longitudinal
dissociation, with the volume of Cx40 expression decreasing compared
with that at the former level (elliptical area). Cx40 expression was not
present on the atrial side. (I) Masson’s trichrome staining showed the
inferior extension of the AVN located on the atrial side above the
tricuspid annules. (J) AChE staining was limited to the INE area. (K)
Cx43 expression was absent in the inferior extension where HCN4
expression was present. The inferior extension divided into the right
extension and the left extension (arrow). (L) Cx45 expression was more
abundant in the INE than in other atrial areas (a slight fold in the
section). No Cx40 expression was observed in the inferior extension.
Figure B(a) shows the location of images shown in Figures C(a) and D(a),
while Figure B(b) shows the location of images shown in Figures C(b) and
D(b). Figure F(a) shows the location of images shown in Figures G(a) and
2H(a), while Figure F(b) shows the location of images shown in Figures
G(b) and H(b).
Figure 3. Continuous sections at the level of start of the CN
and the end of the RN from another sample. (A1-A3) Part of the node-like
tissue was separated from the RN and penetrated into the fibrous rings
between the atrium and ventricle (dotted box). (B1-B3) The following
continuous sections showed that the nodal tissue continued in the
fibrous rings. (C1-C3) The following continuous sections showed that the
nodal tissue descended into the CN. (A3, B3, C3) HCN4 labeling further
suggested that the penetrated tissue was node-like tissue (dotted box).
(D-F) The region connecting the RN and CN was also near the start of the
tendon of Todaro (black arrow). Two narrow connections between the RN
and CN at different levels near the tendon of Todaro (dotted box). After
the node-like tissue descended into the CN, fibrous tissue surrounding
the other part of the CN seemed to have no direct connection with the
atrium.
Figure 4. (Left) Eighty model sections. The distance between
groups is 6 * 4 = 12 μm. (Right) Anatomical model views of the rat
atrioventricular node (AVN). (A and B) Nodal tissue model viewed from
the right and left. (C and D) Nodal (yellow) and penetrating bundle
(red) tissue models viewed from the right and left. (E and F) Conduction
system tissue and valve ring (blue) model viewed from the right and
left.
Figure 5. (A) Nav1.5 expression was abundant in
the atrial and ventricular muscles but weak in the PB and RN.
Cav3.1 was mainly expressed in the PB and RN. (B) and
(C) The CN and INE also weakly expressed Nav1.5 but
positively expressed Cav3.1. (D) Analysis of the
Nav1.5 immunofluorescence staining intensity showed that
the RN, CN and INE all presented significantly low
Nav1.5 expression (P <0.001). No
significant differences in expression were observed among the RN, CN and
INE (P =0.104), but a trend toward slightly higher
Nav1.5 expression in the RN than in the other two
regions was observed.
Figure 6. Hypothesis of the structure and functional
relationship of the AVN. (A) During sinus rhythm, the action potential
propagates preferentially along the RN due to the presence of fewer
connective tissue barriers to the atrial tissue. (B) In the slow-fast
form of AVNRT, anterograde conduction occurs through INE inputs, and
retrograde conduction occurs through the RN. Multiple breakthroughs of
atrial activation occur during A-V nodal reentry due to the dispersed
distribution of the RN.