DEMONSTRATION OF REENTRY WITHIN THE CANINE SPECIALIZED CONDUCTION SYSTEM

There is suggestive evidence that bundle branch re-entry occurs in man in response to premature right ventricular stimulation. Demonstration of the activation sequence during re-entrant excitation in the in vivo dog was accomplished by placing recording electrodes on the major portions of the specialized conduction system. A temporary right heart bypass was utilized to place two or more electrodes on both right and left bundle branches and place electrodes on the His bundle and on the left and right ventricular endocardium. Premature excitation of the right ventricle was found not to retrogradely activate the right bundle but was able to cause slow right to left myocardial activation that resulted in retrograde activation within the left bundle branch. Retrograde conduction in the left bundle caused activation of the His bundle and the proximal right bundle. Activation of the right bundle resulted in antegrade conduction of the impulse across the site of previous conduction block and re-excitation of the right ventricle, to complete the re-entrant circuit. This type of re-entry, utilizing the bundle branches, was demonstrated in 19 dogs. This re-entry circuit was found to be facilitated by shortening of the right ventricular refractory period by local epicardial warming and was abolished by interruption of conduction in the right bundle by anodal blocking current applied to the right bundle. The sites of slow conduction, site of unidirectional block, and pathways of conduction were demonstrated. The validity of the concept of re-entry occurring within the specialized conduction system is substantiated. © 1979.