Introduction
The atrioventricular node (AVN) lies within the triangle of Koch and is
bound by the coronary sinus, tendon of Todaro
and tricuspid valve. The
AVN
functions by conducting action potentials at an appropriate conduction
velocity from the atria to the ventricles. The AVN also acts as a backup
pacemaker in the case of sinus node failure. On the other hand, the
AVN
is part of the underlying circuitry that causes AVN reentrant
tachycardia
(AVNRT).1Inferior nodal extensions (INEs) are part of the
AVN,1-5 and characteristics of these structures are
conserved among various species, including humans,2rats,3 mice,4rabbits5 and dogs. Moreover, it is thought that these
extensions may be involved in slow-pathway conduction and are part of
the underlying circuitry that causes AVNRT, which is supported by
electrophysiological studies.6,7 The use of catheter
or surgical techniques targeting injuries in this region is thought to
be the best method for curing these forms of
tachycardia.7 However, there are still some
electrophysiological phenomena that cannot be explained by relying only
on these anatomical structures, as the exact circuitry responsible for
reentrant tachycardias in different types of AVNRT remains unknown.
Complex anatomical structures and functional longitudinal dissociations
are considered important in understanding the behavior of these
tachycardias.1 Other conduction tissues may also
participate in the real mechanism of AVNRT. The retroaortic node (RN)
has been described as a heap of node-like tissue located on the right
side of the atrium neighboring the aorta.8 Previous
studies have described the anatomical features of this region and its
relationship with the compact node (CN) in little detail. The potential
electrophysiological function of these node-like tissues also remains
unknown.
The aim of this study was to comprehensively analyze the detailed
anatomical structure and histological features of this node-like tissue
and better understand its electrophysiological behavior in normal AV
conduction and AVNRT.