Saroja Bharati.
Maurice Lev Congenital Heart and Conduction System Center, The Heart Institute
for Children, Hope Children's Hospital, Christ Hospital and Medical Center, Oak Lawn, Rush
Medical College, Rush University, Rush-Presbyterian-St. Luke's Medical Center, Chicago,
Finch University of Health Sciences, Chicago Medical School, North Chicago, University of
Illinois at Chicago, Chicago, USA
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The morphology of the atrioventricular (AV) junction
includes the distal part of the atrial septal wall, the eustachian valve, the tendon of
Todaro, the coronary sinus, the approaches to the AV node, the AV node, the AV bundle, the
beginning of the bundle branches, the anuli of the tricuspid mitral and aortic valves, -
the central fibrous body - as well as the membranous part of the atrioventricular septum.
Since all of the above structures are intimately related to each other, variations in any
one of the above may alter the location, size and shape of the various parts of the
conduction system.
The variations in the AV junction:
1) The size of the approaches to the AV node. This may vary considerably, that is, the
posterior approaches may be larger than the superior (anterior) approaches and the left
sided approaches or the left-sided approaches and the superior (anterior) approaches may
be larger than the posterior approaches.
2) The size of the node. The size of the node varies considerably. It may be small,
large or flattened.
3) The location of the AV node. The node in the beginning may be entrapped, in part,
within the central fibrous body. In some cases the node may be more to the left or to the
center part of the atrioventricular septum rather than in its normal location. Or, the
node may be closely related or even entrapped within the tricuspid valve anuli or the
mitral and in extreme cases close to the anulus of the aortic valve.
4) Accessory connections to the AV node. Some of the approaches to the AV nodal
myocardium may be entrapped within the central fibrous body and may incorporate into the
AV node itself. Likewise, node like structures may enter either from the left atrial or
mitral valve and may join the AV node within the central fibrous body.
5) Atrioventricular bundle. The size of the AV bundle varies considerably. At times,
the AV bundle may be quite small and fragmented. On the other hand, the bundle can be
quite large and may occupy almost the entire membranous part of the atrioventricular
septum.
6) Location of the bundle. The bundle may mostly be situated to the right ventricular
aspect or the bundle may be situated to the left ventricular aspect. Rarely the bundle may
be situated within the tricuspid valve.
7) Accessory connections to the AV bundle. Fibers from the atria, either from the
right or the left side, may join the AV bundle bypassing the node. Occasionally, the nodo
bundle junction may be quite abbreviated and it will be difficult to differentiate where
the node ends and where the bundle begins.
In summary, at the gross level, the AV junctional area is of considerable size and
varies from patient to patient and this may have significance during the ablative
procedure. Likewise histologically, the fibers of the conduction system and the
myocardium, including the connective tissue, elastic tissue and the nerve elements, vary
in size, shape and orientation in all of the above areas. It is therefore important for
the electrophysiologists to be aware of the possible abnormal locations of the various
parts of the conduction system. Likewise, the abnormal location of the surrounding
structures and their relationship to the varying parts of the conduction system should be
well delineated before the ablative procedure. The anatomy of the AV junctional area and
its variations are important considerations for further improvement in the field of
ablative therapy.
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