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Figure 1 Distinguishing far-field (FFP) and local potentials (LP) from analysis of entrainment (A) or the effect of radiofrequency ablation (B) are shown. In both panels ventricular tachycardia with a cycle length of 550 ms is present. From the top are surface electrocardiogram leads (I, aVF, V1, V6) and bipolar intracardiac electrograms recorded from the distal (Abl D) and proximal (Abl P) electrode pairs of the ablation catheter. Potentials are labeled 1, 2, and 3. Entrainment indicates potential 1 is an FFP. Radiofrequency ablation reduces the amplitude of potential 3 (B) indicating it is an LP, but does not affect potentials 1 and 2. See text for discussion. Time lines are 20 ms.