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Figure 4 Pulmonary vein tachycardias in ACH. (A) A representative episode of sustained tachycardia (CL = 75 ms) induced with a premature extrastimulus delivered at DS. (B) Dashed box highlighted in A. A premature beat delivered from PS during PV tachycardia advanced the next beat of tachycardia (interval = 45 ms), demonstrating a positive resetting response. (C) An example of double potentials (arrows) recorded during another episode of PV tachycardia originating in PS. (D) Wavefront propagation of PV tachycardia recorded by optical mapping. The trajectory of wavefront propagation took a repetitive clockwise course, verifying re-entry as the mechanism underlying the PV tachycardia, and also demonstrated that the entire re-entrant circuit was confined to PV. Note that the tachycardia circuit was oval (not circular), and the conduction velocity was not uniform along the circuit. Frames are 32 ms apart. *Indicates the leading edge of wavefront. White dots outline the margin of the preparation. ACH = 10^–7 mol/l for all. Abbreviations as in Figures 1 through 3.