Examples from 2 different patients with history of infarction. (A) Pacing the right ventricular apex (RVA) forms the first QRS complex. The distal mapping catheter was positioned at the left ventricular apical septum and recorded a fractionated signal (Map D). The 2 sequential QRS complexes are spontaneous ventricular premature contractions (PVCs) from the basal lateral and septal regions of the left ventricle, respectively. The propagation of these 2 PVCs results in formation of isolated late potential (arrows) that was not present during RVA pacing. (B) Sinus QRS beat followed by PVC from the left ventricle. Once again, development and timing of the late potential (arrows) is influenced by the activation pattern.