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Figure 4 Electrical isolation of pulmonary vein (PV). Pacing threshold from within the PV was determined before ablation. After the intracardiac echocardiography (ICE)-guided circumferential lesions were created, pacing thresholds were again determined. Electrical isolation was defined by dissociation of an ectopic focus from within the vein or loss of PV potentials with pacing threshold distal to the ablation line exceeding 20 mA. (A) An ectopic focus is noted within the vein but does not conduct into the atria and is dissociated from the sinus rhythm. (B) Pacing from within the vein distal to the ablation line at 20 mA fails to conduct to the atria. DCS = distal coronary sinus; HALO = duodecapolar catheter in right atrium; MAP D = distal bipolar of mapping catheter; MAP P = proximal bipolar of mapping catheter; MCS = middle coronary sinus; PCS = proximal coronary sinus.