Delineation of AV conduction pathways by selective surgical transection: effects on antegrade and retrograde...

The role for transitional cells as determinants of AH and HA conduction was examined in the superfused rabbit AV junction.

Bipolar electrodes and microelectrodes were used to record antegrade A-H and retrograde H-A activation, before and after transection of the transitional cell input to the compact AV node.

During pacing from the high right atrium, inferior to the coronary sinus os, beneath the fossa ovalis, or on the anterior limbus, AV Wenckebach block (WB) was mediated by identical transitional cells grouped in close apposition to the compact AV node. Paced WB cycle lengths were shorter from the high right atrium (196+/-12 msec) and inferior to the coronary sinus os (195+/-8 msec) versus the fossa ovalis (217+/-9 msec) or anterior limbus (206+/-11 msec). With His bundle pacing, retrograde HA WB (211+/-17 msec) was observed within the N cell region within the compact AV node. After transection of posterior and superior transitional cell input to the compact AV node, the antegrade AH WB cycle length was prolonged (245+/-18 msec), with an increased WB incidence within the NH region (compact AV node)(5% to 41%; p=0.014). The incidence of retrograde HA WB determined within the NH region was increased (30% to 88%), with a decrease in the stimulus-fast pathway conduction time (98+/-7 to 49+/-6 msec; p<0.01).

The data demonstrate (1) a common transitional cell population determining AH WB, independent of atrial stimulation site, and (2) a plasticity of transitional cell-compact AV node connections, with rapid AH and HA conduction favored by removal of posterior/superior AV nodal input.