PMC4309504_01
Right ventricular apical (RVA) pacing at an S-S cycle length of 380 milliseconds induced a long RP tachycardia, with the earliest site of atrial activation at the ostium of the coronary sinus (A5-6), following an initial "V-A-A-V" electrogram sequence. The numbers between the atrial electrograms on the A 5-6 channel indicate the cycle length in milliseconds. See text for further explanations. I, II, and V1 = surface electrocardiogram; HBE 1-2 and 3-4 = distal to proximal His bundle region; a 9-10 to 1-2 = proximal to distal CS recording.
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fig01
During intravenous administration of isoproterenol, the earliest site of atrial activation during ventricular pacing was observed near the His bundle, and a previously recorded narrow QRS tachycardia was reproducibly induced by premature or rapid ventricular apical pacing, with an initial V-A-A-V activation sequence (Fig.1).