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Figure 1 Panels A and B depict electrocardiographic (ECG) strips from one ventricular fibrillation (VF) storm patient who underwent ablation. Panel A shows a monomorphic premature ventricular contraction (PVC) (*) initiating non-sustained polymorphic ventricular tachycardia. Panel B shows the same morphology PVC (*) initiating VF. Panel C depicts surface ECG (I, II, III, AVR, AVL, AVF, V1, V2, V3, V4, V5, V6) and intracardiac recordings from the ablation catheter (ABLp). The vertical caliper lines on the third beat of the tracing () indicate a high frequency potential preceding the PVC by 70 ms. Similar high-frequency Purkinje-like potentials are also seen during the two sinus beats that precede the PVC (arrows). Similar potentials were seen in patients without spontaneous PVCs along the scar border.