ANATOMIC SUBSTRATE OF THE EXPERIMENTALLY-CREATED ATRIOVENTRICULAR NODE REENTRANT TACHYCARDIA IN THE DOG

Despite major success in the treatment of atrioventricular (AV) node r eentrant tachycardia using either catheter ablation or surgery, the mo rphologic basis underlying AV node reentry is not yet clear. A canine model of AV node reentrant tachycardia was used to examine the histolo gic features of the reentry circuit. AV node reentrant tachycardia was created in 4 of 8 dogs by a right atrial division which divided the r ight atrial free wall and the atrial septum into upper and lower porti ons on a plane between the mid-right atrial free wall and the fossa ov alis. The AV junctional area of all dogs were serially sectioned on a plane that was perpendicular to the AV annulus and the septum. The sli ces were stained with Masson's trichrome technique, The connections be tween atrial fibers and the compact AV node and the common AV bundle w ere examined, and comparison of the histologic features between dogs w ith and without AV nodal re-entry was made. The histologic examination s showed that, in all dogs, the operation scar was remote from the AV junctional area leaving the Koch's triangle intact. The compact node r eceived its atrial inputs mainly from the anterosuperior and posterior aspects of the Koch's triangle, However, both atrial inputs gave off superficial (subendocardial) fibers that by-passed the compact node to terminate at the base of tricuspid valve, These superficial fibers mi ght function as the proximal link between the dual AV nodal inputs by means of lateral connections, There was no bypass connection between a trial fibers and the common AV bundle, The histologic features of the AV junctional area was not different between dogs with and without AV nodal reentry. In conclusion, AV nodal reentry involves the anterior a nd posterior atrio-nodal inputs which function as dual AV nodal pathwa ys, and the superficial bypass fibers form the proximal linkage betwee n the two inputs. These structures, together with the compact node, co mplete the reentry circuit.