Innervation principles of the sinoatrial and the
atrioventricular nodes
In physiological experiments in canine and primates, removal of the
epicardial ganglia located at the junction of the inferior vena cava and
inferior wall of the LA eliminated the negative dromotropic effects of
vagal nerve stimulation without suppressing vagally mediated reductions
in heart rate (6, 7, 38, 39). On the contrary, surgical removal of the
epicardial ganglia and nerves located around the right PVs attenuated
the negative chronotropic response to vagal nerve stimulation without
adversely affecting vagal inhibition of atrioventricular conduction (6,
7). In the human heart as well as in the hearts of some other mammalian
species, both the VRAsGP and the DRAsGP supply epicardial
nerves to the sinoatrial nodal neural network (Figure 2 and Online
Supplemental Figure 1) (40, 41). Although the size and number of ganglia
inside these sGPs vary from one heart to another, the largest number and
density of epicardial ganglia are usually located at the junction of the
SVC with the RA. It is noteworthy that some part of the postganglionated
nerves of the VRAsGP passing onto the LA invariably extended via
a remarkable crest of the ventral surface of the LA. This anatomical
distribution should be kept in mind to understand why bi-atrial ablation
might be needed for complete denervation of the sinoatrial node in some
cases (Figure 4). Despite results of physiological experiments,
successive anatomical attempts to determine nerves that coursed towards
the canine or ovine atrioventricular node failed as those endocardial
nerves are especially tiny (33-35). However, postganglionated nerves
from the LDsGP , and the MDsGP extend towards the
interatrial septum and presumably supply the atrioventricular nodal
region (Figure 4) (33-35).