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Figure 2 Mapping catheter recordings of a sinus beat and the first beat of repetitive monomorphic ventricular tachycardia (RMVT) at the successful ablation sites in two different patients. Each panel shows surface electrocardiographic leads I, III and V4, as well as the bipolar and unipolar signals recorded from the mapping catheter. (A) Earliest ventricular activation preceding onset of the QRS complex by 34 ms in a patient with RMVT originating from the left coronary aortic sinus. The unipolar signal (AS uni) also has a QS morphology, but is activated later than the bipolar signals (AS 1–2). Please note that a low-amplitude presystolic potential (arrow) appears during RMVT, although this potential is the second component of the "ventricular signal" (asterisk) during sinus rhythm. (B) Earliest low-amplitude late-diastolic ventricular potential (arrow) preceding onset of the QRS complex by 97 ms in a patient with RMVT originating from the left coronary aortic sinus cusp. As in part A, this potential is also seen as the second component of the "ventricular signal" during sinus rhythm (asterisk). A = atrial potential; V = ventricular potential.