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Figure 4 (Top to bottom) 12-lead surface electrocardiograms, endocardial signals from the right ventricle, and epicardial signals from the left ventricle corresponding to two different ventricular tachycardias in the same patient. (Left) Epicardial signals show fractionated electrograms of high voltage present during the diastole preceding the QRS complex. (Right) Epicardium signals show an isolated diastolic potential followed by a fractionated electrogram preceding the QRS complex. In these sites, radiofrequency ablation effectively terminated the tachycardia depicted in the 12-lead electrocardiogram.