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Figure 3 Recordings obtained during programmed stimulation in sinus rhythm (baseline cycle length S1–S1, 500 ms) approximately 0.5 cm anterior to the crista terminalis at bipole 1/2 of the pacing catheter (Patient #10). The surface leads I, II and III and the intracardiac electrograms recorded at successive bipoles of the pacing (Pace) and the crista terminalis (CT) mapping catheter are shown. Bipole 1/2 refers to the most superior and bipole 9/10 to the most inferior pair of electrodes. Catheter position as in Figure 1. (A) Baseline pacing with a pacing cycle length S1–S1 of 500 ms as well as an atrial premature beat with a coupling interval S1–S2 of 430 ms resulted in continuous electrograms at all bipoles of the CT catheter. The width of local activation was relatively short, for example, 50 ms at bipole CT1/2. The atrial activation at the CT showed a sequence from the pacing site at the superior aspect of the right atrium toward the inferior right atrium (arrows). (B) A decrease of the coupling interval S1–S2 from 430 to 310 ms resulted in a significant prolongation of local activation, for example, from 50 ms to 80 ms at bipole CT1/2, indicating a conduction delay. Two components (A and B) of the fractionated potentials could be distinguished. However, no isoelectric interval was present and the activation sequence remained unchanged. (C) After extrastimulus testing with a further 20 ms decrement of the coupling interval (S1–S2, 290 ms), local electrograms at the CT mapping catheter showed a marked prolongation, for example, 105 ms at bipole CT1/2, and the two components became separated by an isoelectric interval. With the occurrence of split potentials, a marked alteration of the activation sequence of the second component of split potentials was found. As can be appreciated from these findings, a conduction block developed at the CT mapping catheter that was not present during atrial premature beats with longer coupling intervals.
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