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©2013 UpToDate ® Print Email 2:1 intra-Hisian block The baseline 12-lead electrocardiogram in this patient demonstrated sinus rhythm with 2:1 AV block with normal conducted P-R intervals and a narrow QRS complex. All 12 surface leads are shown. Representative intracardiac tracings are the proximal His bundle electrogram (HIS p) and the distal His bundle electrogram (HIS d). Every other atrial depolarization is followed by a His, but no ventricular depolarization (arrows) indicating either intra-Hisian block where a H' could not be recorded or infra-Hisian block. Given the normal P-R intervals and QRS complexes, intra-Hisian block is favored. A: atrial depolarization; AV: atrioventricular; H: His bundle depolarization; V: ventricular depolarization. Courtesy of Joseph J German, DO.