Cocaine-Induced Incomplete Bundle Branch Block in Dogs

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Abstract
Cocainization of a segment of the right or left bundle branch in the canine heart permitted observation of the phenomenon of incomplete bundle branch block in its dual expressions, namely, alterations in the action potential of the respective bundle branch and alterations in the ventricular complexes of the limb-lead electrocardiogram. As the effects of cocainization waned, the bundle action potential reflected intermediate stages between complete block of conduction and normal conduction. Likewise, the attendant ventricular complexes reflected intermediate stages between that form traditionally associated with complete block of the corresponding bundle and normal form. Characteristic shift in direction of the near-terminal QRS axis occurred with and without significant prolongation in QRS. Cocainization of a segment of the common bundle resulted in first, second, or third degree atrioventricular block, unattended by changes in form of associated ventricular complexes. As in bundle branch block, regression of common bundle block occurred also in stepwise fashion.

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