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Figure 3 The local electrogram from the epicardial aspect in the patient in Figure 1 is shown on the left side of the panel. The ventricular electrogram precedes the surface QRS by 63 ms, but there is also a large atrial electrogram recorded at this site. The right side of the panel shows local activation recorded from the left aortic sinus of Valsalva where the ventricular tachycardia was successfully ablated. At this site the local ventricular electrogram preceded the surface QRS by 52 ms.