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Figure 3 Example of a Multiple-Loop AT Circuit
(A) Activation map of the left atrium (LA) in a posteroanterior (PA) view. There is counterclockwise activation along the posterior wall. The pink tags show the course of the esophagus. (B) Activation map of the LA in a shallow left anterior oblique view. There are 2 more loops, one with clockwise activation along the anterior wall (white loop) and another with clockwise activation (yellow loop) around the mitral valve (MV). The latter is consistent with an epicardial mitral isthmus circuit utilizing the coronary sinus (CS). The dashed brown portion of the mitral-isthmus loop refers to activation along the posterior wall. The loops along the anterior and posterior walls converge at the roof. The ostial aspect of the CS was also shown to be part of the circuit by entrainment mapping (Fig. 4), making it a quadruple-loop circuit. The mitral isthmus loop was targeted first, and ablation was commenced at the distal CS because there were no appreciable electrograms at the endocardial aspect of the isthmus. See Figures 4 and 5 for further details. Note the presence of scar (gray circles), especially at the mitral isthmus. AT = atrial tachycardia.
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