Conduction Disorders in the Canine Proximal His-Purkinje System Following Acute Myocardial Ischemia

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Abstract
The evolution of bilateral bundle branch block (BBB) was studied in ten anesthetized dogs by recording electrical activity from the bundle of His (Hb), right (Rb) and left bundles (Lb) for precise localization and characterization of the conduction disorder. Records were obtained before and at intervals up to 8 hours after ligation of the anterior septal artery. Forty to 140 min after ligation conduction was impaired in either the Rb or Lb showing complete BBB both at rapid heart rates (tachycardia-dependent) and slow rates (bradycardia-dependent) with normal QRS or incomplete BBB at control rates. Later complete BBB became constant at all heart rates. When both bundles were significantly involved, various combinations of intraventricular and atrioventricular conduction disorders occurred. Unequal delay in both bundles (unequal 1° bilateral BBB) gave rise to prolonged H-V interval and a QRS pattern of incomplete or complete bundle branch block corresponding to the branch in which the conduction delay was greater. Equal delay in both bundles gave rise to a narrow QRS with prolonged H-V interval. Second degree block in one bundle and complete (3°) block in the other manifested as 2:1, Mobitz type II, or Wenckebach A-V conduction disturbance. Unequal and asynchronous 2° bilateral BBB gave rise to complex patterns of alternating BBB associated with alteration in the H-V interval of 25-35 msec. In two experiments showing alternating BBB, longitudinal dissociation and asynchronous conduction in the distal Hb was suggested.