The existence of a variety of unique electrophysiological fi
The existence of a variety of unique electrophysiological findings, such as antegrade triple AVNPs, latent retrograde dual AVNPs, and compact nodal reentry due to the presence of subatrial upper and intranodal lower final common pathways, is uncommon. Furthermore, it caspase inhibitor is very uncommon that the DVR of one sinus beat and an eccentric pattern of the slow–fast typical AVN echo as preceding a His potential could be observed in the same patient. With regard to the eccentric atrial echo, Josephson  stated that the early retrograde P wave can be rarely detected as the ‘pseudo-Q wave’ in inferior leads and that this phenomenon was based on the conduction delay below the circuit in a lower final common pathway. However, to our knowledge, it has never been reported that the typical AVN echo markedly precedes the H2 potential before RFA (Fig. 2B). Accordingly, we hypothesized the mechanism of the eccentric Ae as follows: despite the fact that the decrease of the A1A2 interval from 320ms to 300ms could provoke the marked prolongation of the AV conduction time to as long as 170ms (550−380ms), the increment of the interval from the S2 to the initial Ae was just 40ms (420−380ms). Assuming that the lower turnaround point of the antegrade AVNP to the retrograde fast pathway was fixed and the retrograde conduction time through the fast pathway was constant, the 40-ms increment should correspond to the difference of conduction time for each A2 impulse at A1A2 intervals of 320ms and 300ms to reach the lower turnaround of the antegrade AVNP. Therefore, the remaining prolongation of the AV interval, 130ms (170−40ms), should be occupied by conducting over the lower final common pathway. If this is the case, the eccentric Ae should be induced by the A2 impulse antegradely conducting over the slow but not the very slow AVNP and retrogradely going up the fast AVNP, which indicates the jump-up within the lower final common pathway rather than that from the slow to the very slow AVNP, therefore, the longitudinal dissociation has to exist within the lower final common pathway as well, probably the intranodal portion. Although the hypothesis may not seem to be in favor of the presence of the antegrade very slow AVNP, the very long initial Ae–He intervals (720ms and 680ms in Fig. 2A and B, respectively) strongly suggested the existence of the antegrade very slow pathway rather than the excessively decremental conduction in the slow pathway. Alternatively, the lower turnaround of the very slow AVNP was localized to the more proximal site than that of the slow one, so the eccentric Ae appeared. This assumption can be definitely denied by the fact that the second Ae depolarization following the first Ae impulse, conducting in an antegrade fashion down the very slow pathway and in a retrograde fashion up the fast pathway, appeared after the first He as shown in Fig. 2A and B. It is also important to prove that the eccentric Ae beat was not based on other reentrant circuits except the AVN, e.g., intra-atrial reentry originating near the AV node. Although it is not easy to completely exclude this intra-atrial hypothesis, the finding that the Ae induced with A1A2 intervals of 320ms and 290ms before RFA could be rendered noninducible after elimination of the antegrade slow and very slow AVNPs by RFA (Fig. 3A and D) can become greatly disadvantageous to the hypothesis. Moreover, RFA applied to the usual slow pathway areas could abolish both the antegrade slow and very slow AVNPs below the distal end of the retrograde slow pathway and above the HBE as shown by Inoue et al. . This indicates that both the antegrade slow and very slow pathways partly existed in the inferior nodal extension emanating from the compact node (Fig. 4B). Finally, although the phenomenon of DVR can be rarely observed , it can occur theoretically with the conditions that an antegrade conduction time over a slow (or very slow) AVNP is longer than the effective refractory period of tissue below a lower turnaround point produced by an impulse conducting over an antegrade fast pathway and that there is little or no linkage between the antegrade fast and slow (or very slow) AVNPs . The presence of antegrade triple AVNP may be a great advantage of this phenomenon.