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  • br Initially extrastimulation from the RV at

    2019-04-26


    Initially, extrastimulation from the RV at a basic CL of 600ms showed no jump-up phenomenon and VA conduction block at a coupling interval of 480ms (not shown in the figure). The antegrade AVN conduction was evaluated by extrastimulation from the HRA and the ostium of the CS (CSp) at a basic CL of 600ms. Panels A and B show the surface ECG leads and the intracardiac recordings obtained by the HRA-programmed extrastimulation with A1A2 coupling intervals of 320ms and 300ms, respectively. In panel A, the extrastimulus could induce a typical slow–fast type of AVN reentrant atrial echo (Ae) following a long AV conduction time (380ms; the second stimulus artifact (S2) to QRS onset in lead II) after an antegrade fast AVNP conduction block (the effective refractory period of 330ms as shown in Fig. 4A). Moreover, the Ae impulse reached the His bundle (He) requiring a very long conduction time of 720ms, which probably indicates the conduction through a very slow AVNP, leading to the itk inhibitor of a typical AVNRT with a CL of 510ms. Similarly, in panel B, the extrastimulus provoked a marked long AV conduction time (550ms), implying the prolongation of 170ms compared with that of 320ms and the second jump-up phenomenon from the fast pathway so the impulse could yield an eccentric Ae showing an A2–Ae–H2 (–V2) sequence with an Ae–H2 interval of 100ms (shown with a bidirectional arrow). Thereafter, the Ae impulse again resulted in the production of a typical AVNRT after conducting down the very slow pathway (Ae–He time of 680ms). Notice that the atrial activation sequence of the last 2 Ae depolarizations was subtly different from that of the first Ae, which shows that its depolarization on the distal HBE (HBEd) electrogram is registered slightly earlier than that on the CSp electrogram, on the other hand, the last 2 Ae activation sequences seem to be different from that of the first Ae, although the last 2 Ae depolarizations on the HBEd electrogram cannot be confirmed because of fusion with the ventricular depolarizations. This peculiar finding is explained later. Similarly, extrastimulation at 290ms could result in a further prolongation of the AV conduction time (570ms) and provoke a similar eccentric Ae and AVNRT (not shown in the figure). However, no echo appeared at the ≤280ms-A1A2 intervals irrespective of a sufficient AV interval (not shown in the figure). These phenomena could be observed by programmed stimulation from the CSp as well. Panel C shows that the AV dissociation based on the His-atrial block (HAB) was observed during the AVNRT, which suggests that the upper final common pathway existed in the subatrial tissues such as the AN and the N regions, therefore, the atrial myocardium was not a necessary link in the circuit. Thus, the above-mentioned different atrial activation sequence of the Ae depolarizations illustrated in panel B may be explained by the presence of multiple atrial inputs outside the upper final common pathway of the tachycardia circuit [5–7]. Namely, if the atrial input shifts toward the CSp, the relationship between the Ae depolarizations on the HBEd and on the CSp electrograms may be variable. The fourth atrial depolarization (As) from the left in panel C could go down both the antegrade fast (AH time, 140ms) and the antegrade very slow AVNP (AH time, 630ms) simultaneously (double ventricular responses [DVR]) [4,8], whereas the tachycardia appears to continue. This finding probably implies that the As impulse could penetrate the reentry circuit by conducting down the fast AVNP, and since the refractoriness of the tissue below the HBE yielded by the impulse was shorter than 490ms (630−140ms), the other impulse conducting down the very slow AVNP could reach the ventricle and reset (or reinitiate) the tachycardia. Subsequently, RFA using a 4-mm tip ablation catheter was performed at the maximal power of 50W and a temperature of 60°C. Energy applications were performed under fluoroscopic guidance at sites with multicomponent atrial potentials and atrial–ventricular amplitude ratios of 1/10 to 1/7 irrespective of the presence of a slow pathway potential. Energy was initially delivered near the bottom of the CSp. If an accelerated junctional rhythm (AJR) appeared by 30s, RFA was continued up to 120s, however, if it did not, RFA was terminated and repeated at sites a little above the initial delivery point up to half the height of Koch\'s triangle. Successful ablation required a total of 8 delivery times and a duration of 581s with no procedure-related complications, such as transient AV or VA blocks.