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©2013 UpToDate ® Print Email 2:1 AV nodal block The baseline 12-lead electrocardiogram in this patient demonstrated sinus rhythm with 2:1 AV block, prolonged AV conduction, and a left bundle branch block. Surface leads represented are I, II, III, V1, and V6. The intracardiac tracing shown is the distal His bundle electrogram (HIS d). Every other atrial depolarization is not proceeded by either a His or ventricular depolarization (arrows) indicating AV nodal block. A: atrial depolarization; AV: atrioventricular; H: His bundle depolarization; V: ventricular depolarization. Courtesy of Joseph J Germano, DO.