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Figure 2 An example of withdrawal mapping in the cavotricuspid isthmus and ablation in a patient with preexisting partial cavotricuspid isthmus block. Left panel: A sequentially reconstituted withdrawal map in a patient before ablation during counterclockwise atrial flutter from the tricuspid valve (TV) edge to the inferior vena cava (IVC) edge. The atrial electrograms have been synchronized to the same timing with reference to the central dotted line bisecting the plateau in inferior leads on the surface electrocardiogram. Narrowly separated small double potentials (DPs) (arrows) are noted at the TV edge (top), followed by a fractionated potential centered on the reference line (star). During continued withdrawal, separated DPs are again noted. This interval widens progressively with further withdrawal as a result of an increasing delay of the second potential, as shown in the bottom three electrograms. Right panel: A single radiofrequency application at the fractionated electrogram site (star) terminated flutter 3.5 s later and produced bidirectional isthmus block. Note that termination occurs exactly in the center of the surface electrocardiographic plateau. Scale bars indicate 0.1 mV and 100 ms. V = ventricular electrogram. I, II, III, avR, avL, avF, V1–V6 = surface ECG leads.
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