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Figure 6 Recordings from case 19 showing induction of sustained fast-slow atrioventricular node reentry tachycardia and variation of P-QRS relation with block proximal to the His bundle recording site following intravenous bolus of 3.5 mg adenosine triphosphate. (A) A sustained fast-slow atrioventricular node reentry tachycardia was induced following rapid ventricular pacing at a cycle length of 300 ms. Note the tachycardia was induced after the fourth ventricular paced beat during an atypical retrograde Wenckebach periodicity when conduction shifted from the fast to the slow pathway. The cycle length of the tachycardia varied between 290 to 310 ms, AH 70 to 90 ms and HA 220 ms. (B) After adenosine triphosphate, a prolongation of AH between 90 to 130 ms, a variation of the tachycardia cycle length between 310 to 320 ms and a shortening of HA between 230 to 190 ms were noted before a blocked beat (indicated by a star) occurred. This was then followed by an episode of 3:2 block proximal to the His bundle recording site (indicated by stars) with progressive lengthening of the tachycardia cycle length and, then, termination of the tachycardia. s = stimulus artifact.
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