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Figure 2 Isochrone Map and Local Electrograms During Sinus Rhythm and LA Flutter

(A and B) The typical activation pattern in the left atrium (LA). The wavefronts propagating around the gray zone, where isochrone lines crowded together and double potentials were recorded during sinus rhythm in the anteroposterior and left posteromedial view, respectively. (C and D) Activation of a figure-of-eight LA flutter with a cycle length of 199 ms. Arrows indicate circuit loop(s). The brown lesion indicates the pulse of circumferential ablation. One loop rotates around the mitral annulus and the other rotates around the left PVs with a common channel conducted through the mitral isthmus. The re-entrant circuits of atrial flutter were bordered anteriorly and posteriorly by lines of conduction block (gray zone), which were in similar locations during sinus rhythm (A and B). (D) Illustrates the local bipolar electrograms along the circuit of double-loop re-entry. Recording positions are shown in the isochrone map. During LA flutter, clockwise atrial activation around the mitral annulus was manifested by atrial electrograms in the middle posterior wall (site 1), lower posterior wall (site 8), medial mitral isthmus (site 9), and lower anterior wall (site 10), followed by activation in the lateral mitral isthmus (sites 5, 11, and 7). A slow conduction zone with fractionated electrograms was recorded at site 5. Another counterclockwise atrial activation around the left pulmonary vein was manifested by atrial electrograms in the middle posterior wall (site 1), upper posterior wall (site 2), roof (site 3), and upper anterior wall (site 4) followed by activation in the lateral mitral isthmus (sites 5, 6, and 7). Labeled anatomical locations include the mitral valve (MV), right superior pulmonary vein (RSPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), and left atrial appendage (LAA).