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Figure 2 Programmed atrial extrastimulation from the HRA and the CS orifice during the middle type of AVNRT. (A) An HRA single extrastimulus is delivered during AVNRT with a stable tachycardia cycle length of 300 to 305 ms. (B) A single extrastimulus from the CS orifice is delivered during AVNRT with a stable tachycardia cycle length of 285 to 290 ms. A0, H0 and V0 = atrial, His bundle and ventricular electrograms of ongoing tachycardia beats before the extrastimulus (S); A1, H1 and V1 = atrial, His bundle and ventricular electrograms immediately after the extrastimulus; A2 and A3 = atrial electrograms following A1; V2 and V3 = ventricular electrograms following V1; CS 3-4 (1-2) = coronary sinus (CS) electrogram recorded by the proximal (distal) pair of electrodes of a quadripolar electrode catheter positioned at the CS orifice; HBE = His bundle electrogram; V1, II = ECG leads V1 and II. Paper speed is 100 mm/s. See text for details.
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