The constant evolution of medical knowledge and accompanying development
of diagnostic and treatment possibilities for arrhythmias and conduction disturbances
has reawakened interest in the structure and function of the conduction
system of the human heart, especially in the region of the atrioventricular (AV)
junction and within the junction itself. Of the large number of studies dealing
with the AV junction few focus on the initial zones of the AV node. These were
described for the first time by Tawara in 1906. Similarly, Anderson et al. distinguished
two origins of the AV node, the left one running towards the basis of
the mitral valve and the right one leading towards the tricuspid valve. The differences
in length and scale could be the result of the adoption of different reference
points.
The study was carried out on the material of 50 human hearts, of both sexes
and ranging in age from 22 to 93, which were fixed in 10% formalin and 98%
ethanol solution. The tissue obtained was fixed in the 10% formalin solution
and, after being sunk in the paraffin, was cut into layers of about 10 μm thick.
According to the age of the hearts, every 10th or 6th section was stained by the
Masson-Goldner method. The preparations were examined under a LEICA 2000
and BIOLAR 2 microscope at magnifications of 2× to 400×.
Each of the 50 examined hearts contained the atrioventricular node and its initial
parts. We observed that the initial zone of the AV node is created by an
assembly of cells typical for a conduction system that can create three groups
that are initially independent of each other and are always arranged around the
AV nodal artery. In all the hearts examined we found at least two initial parts of
the node: the superior and inferior. These two groups were present in 45 hearts
(90%). In the last 5 cases (10%) there was also a middle group. No cases were
found either with a single initial group or without any initial groups. In the
sections examined the superior group appeared to be first in 27 hearts (54%),
while in 23 cases (46%) the inferior group was first. The length of each group
was measured from its first appearance to its first direct contact with the second
part. The length of the superior part varied from 0.15 to 2.91 mm (mean 0.90 ± 0.6 mm), the inferior from 0.11 to 2.41 mm (mean 0.88 ± 0.6 mm) and the middle from 0.67 to 2.21 mm (mean 1.04 ± 0.7 mm). As mentioned above, in
all 50 hearts there was a direct connection between the atrial muscle and the
upper origin of AV node. Furthermore, in all sections (100%) the same part of
the interatrial septal muscle was connected to the compact part of the node.
Additionally, in 3 cases (6%) we were able to observe direct connections between
the muscle fibres running from the fasciculus limbicus inferior to the
initial zone of the AV node: in 2 cases (4%) with the superior group and in
1 case (2%) with the inferior group. In 8% of the material the atrial muscle of
the supra-orificial zone made direct contact with the superior initial group and
the compact zone of the node and in 10% there was contact between the
suborificial muscle and the inferior group and the compact part of the node.
This configuration was not observed in relation to the middle and inferior groups