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Figure 4 Recordings obtained during programmed stimulation in sinus rhythm (baseline cycle length S1–S1, 600 ms; coupling interval S1–S2, 250 ms) at bipole 1/2 of the pacing catheter (Patient #6). Surface leads I, II and III and 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 pair of electrodes, bipole 9/10 to the most inferior. Catheter position as in Figure 1. Baseline pacing resulted in the occurrence of broad but continuous atrial activation at all CT mapping bipoles, suggestive for transverse pulse propagation across the CT. After extrastimulus testing with a coupling interval of 250 ms, split potentials with an isoelectric interval were recorded, indicating a functional conduction block at the CT. The first component of the split potentials represents the depolarization of the anterior aspect of the CT, the second component that of the posterior aspect, respectively. In the presence of conduction block, the pulse propagation at the posterior right atrium shows a sequence from low to high (arrow). Two components (A and B) of the fractionated potentials could be distinguished.
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