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Figure 2 Isopotential maps showing the activation sequence (frames 1 to 6) of single-loop re-entry in the right lateral view. Color scale for each isopotential map has been set so that white indicates most negative potential and blue indicates least negative potential. The activation wave front proceeds through the channel between the CT and the central obstacle (frame 1), activates the low anterior wall (frame 2), and turns around the line of block (frame 3). Then the wave front propagates upward to the roof in front of the right atrial appendage (frame 4), turns around the superior vena cava (SVC) to activate the posterior wall (frame 5), and spreads over the top of the crista terminalis (CT) to complete the re-entrant circuit (frame 6). The virtual electrograms (virtual 10 to 14) on the line of block showed double potentials. HIS = His bundle region; IVC = inferior vena cava; RAA = right atrial appendage; TV= tricuspid valve.