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Figure 6 Recordings obtained during programmed stimulation in sinus rhythm (baseline cycle length S1–S1, 500 ms; coupling interval S1–S2, 330 ms) at bipole 5/6 of the pacing catheter (Patient #7). Recordings, abbreviations and catheter position as in Figure 4. This figure illustrates a typical example of a localized conduction block at the central aspect of the CT. As can be seen, baseline pacing at bipole 5/6 results in a spread of activation from the pacing site toward both edges of the CT mapping catheter. After extrastimulus testing with a coupling interval of 330 ms, split potentials were recorded at bipole 5/6 and bipole 7/8 of the CT mapping catheter. The activation sequence of the first component of split potentials was identical to that during baseline pacing. However, the activation sequence of the second component indicated two wavefronts colliding at bipole 5/6. The descending wavefront emerges from bipole 1/2, the ascending wavefront from a site inferior to bipole 9/10.