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Figure 3 Histograms of 100 F0F1 intervals at three coupling intervals (CIs). (Top) A hundred local FF intervals in a baseline AF recorded at a unipolar atrial electrogram were plotted in a histogram, which showed a symmetrical distribution with a Mode FF of 70 ms. (Middle) The histogram of 100 F0F1 intervals obtained by repeated single extra-stimuli at CI of 65 ms appeared to be asymmetrical in distribution compared with the control histogram. (Bottom) The histogram of 100 F0F1 intervals for repeated single extra-stimuli at a shorter CI of 45 ms showed a symmetrical distribution.