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Figure 3 Anterior left atrial tachycardia focus at the center of the mapping catheter. Demonstrated are the electrograms and a schematic representation of activation. The catheter was positioned directly on the site of the tachycardia focus and resulted in a proximal-to-distal activation on four or five spines of the catheter. In this case, spine-D demonstrates the earliest activity and the smallest activation gradient of all spines. Ablation at this site terminated tachycardia. Note the much smaller relative activation time difference between electrodes on account of the localized mapping, compared to conventional activation mapping. CS = coronary sinus.