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Figure 2 Electroanatomic maps acquired during tachycardia in Patient 3, who had a superior trans-septal approach for mitral valve replacement. (A) Bipolar voltage maps of both atria in a cranial projection. A zone of low voltage is present in the lateral wall of the right atrium (RA), extending superiorly and along the atrial septum. Low voltage is also present in the septal wall and the dome of the left atrium (LA). The blue tag indicates a site of double potentials, and pink tags are fractionated potentials. (B) Isochronal activation map of the RA, in a right anterior oblique projection (isochronal step = 20 ms). The gray area indicates a region of low voltage, and the double brown lines indicate a line of conduction block in the lateral wall. A single re-entrant circuit is present around the lateral wall of the RA involving tissue between scar and the superior vena cava (SVC). This circuit involves tissue with low voltage and fractionated potentials adjacent to the SVC. IVC = inferior vena cava; LSPV = left superior pulmonary vein; RAA = right atrial appendage.