Figure 4. Focal atrial tachycardia originating from the left superior pulmonary vein (LSPV). Electrograms from two decapolar catheters and the mapping catheter (Map) are shown. One decapolar catheter is placed in the coronary sinus (CS) with proximal poles (CS9, 10) at the CS ostium and the other along the free wall of the right atrium (Crista). Panel A shows the CS activation sequence which is earlier at CS3, 4 suggestive of a tachycardia originating from the left atrium. Panel B shows entrainment from LSPV. Notice the similar LA activation sequence during pacing and the post-pacing interval within 20ms of the tachycardia cycle length. Panel C displays the electroanatomical map of the tachycardia.