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Figure 3 Site of successful ablation of a premature ventricular contraction originating from the posterior mitral annulus (Patient #12). (A) Intracardiac recordings. During the premature ventricular contraction, a distinct presystolic potential recorded by the ablation catheter preceded the onset of the QRS complex by 60 ms (arrow). The timing of the second peak of the "notched" Q-wave corresponded precisely with that of activation of the right ventricular free wall (dotted line), which was recorded with the catheter at the high right atrium (HRA). (B) Radiographs obtained in the right anterior oblique (RAO, 35°) and left anterior oblique (LAO, 45°) projections show ablation sites. A distal electrode of the ablation catheter was positioned at the posterior mitral annulus. A = atrial activation; Bi. = bipolar electrogram; Uni. = unipolar electrogram; V = ventricular activation.