M. Antz et al., EVIDENCE FOR MULTIPLE ATRIO-AV NODAL INPUTS IN THE NORMAL DOG HEART, Journal of cardiovascular electrophysiology, 9(4), 1998, pp. 395-408
Introduction: Complete AV block after combined fast pathway (FP) and s
low pathway (SP) ablation is uncommon. The purpose of this study was t
o interrupt activation of these and additional inputs by placing a rad
iofrequency lesion across the interatrial septum between the FP and SP
ablation sites. Methods and Results: In eight anesthetized open chest
dogs, FP ablation induced significant A-H prolongation (Delta A-H: 51
+/-14 msec; P < 0.001) and a shift of earliest retrograde atrial activ
ation from the anterior septum to the region of the coronary sinus (CS
) os. Subsequently, ablation of the interatrial septum across the foss
a ovalis was successful in 5 of 8 dogs, changing the sequence of atria
l activation (A) so that A at the His-bundle electrogram, which initia
lly preceded A at the CS os (18 +/- 4 msec vs 46 +/- 7 msec, P < 0.01)
, now followed CS os A (81 +/- 31 msec vs 59 +/- 20 msec, P < 0.05). A
dditional ablation of the SP caused a type II Mobitz AV block or compl
ete AV block in 5 of 8 dogs. The four dogs with complete AV block show
ed a stable, high junctional escape rhythm at a rate of 64 +/- 16 beat
s/min. Pacing between the ablation lesions and the AV node in one dog
showed 1:1 AV conduction and Wenckebach-type AV block indicating prese
rved AV nodal function. Histology showed necrotic changes in the FP an
d SP transitional cell zones and in the atrial tissue of the interatri
al septum. However, the compact AV node, His bundle, and adjacent atri
a and transitional cells were undamaged. Conclusion: There are additio
nal AV nodal inputs in the interatrial septum in addition to the anter
ior FP and posterior SP inputs. Ablation of all of these may be requir
ed, if the aim is production of complete AV block proximal to the AV n
ode with a high junctional escape rhythm.