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Figure 3 Induction of supraventricular tachycardia during right ventricular extrastimulus testing with a basic drive (S1S1) cycle length of 800 ms (case 2). (A) (S1S2 = 610 ms) The ventricular extrastimulus (S2) is conducted to the atria through an FP, with the earliest atrial activation being registered on the His bundle electrogram (HBE); the resultant A1A2 interval on the CS3-4 electrogram is 720 ms. (B) (S1S2 = 600 ms) The ventricular extrastimulus (S2) is conducted to the atria through an SP, with the earliest atrial activation being registered on the CS3-4 electrogram; the resultant A1A2 interval on the CS3-4 electrogram is 750 ms. Initiation of supraventricular tachycardia is associated with a ventricle-atrium-ventricle sequence and a prolonged A1A2 interval (720 ms  750 ms). Ae, He, Ve1 and Ve2 = atrial, His bundle and ventricular electrograms during the induced supraventricular tachycardia. Other abbreviations as in Figure 2. Paper speed is 100 mm/s.
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