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Figure 1 A schematic of a figure-eight re-entry circuit is shown. The black area represents inexcitable scar tissue. Specific sites in the circuits are indicated by numbers. The sites between 10 and 1 are in the central common pathway, with 1 being an exit and 10 being an entrance. Sites 3, 6 and 9 are in the inner loop, and sites 24, 27 and 30 are in the outer loop of the circuit. A bystander pathway containing site 35 is connected to the central common pathway. The QRS onset occurs after the excitation wave exits from the common pathway at site 1. The borderline between the normal tissue and the infarct tissue is shown by the dotted line. Pacing at sites to the right of the dotted line produces wavefronts that alter activation remote from the circuit, producing QRS fusion.
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