Wedensky facilitation in canine right bundle branch

The phenomenon of Wedensky facilitation was investigated in canine specialized conduction fibers. A segment of block was produced by an electrical depolarizing current of sufficient intensity to result in non-conduction of impulses. A subthreshold stimulus was applied to the preparation distal to the segment of block with a bipolar stimulating electrode. Electrotonic potentials which originated at the proximal block boundary and traversed the segment of block were demonstrated with an intracellular microelectrode. Synchronization of the previously subthreshold distal stimulus with the peak of the transmitted electrotonic potential demonstrated facilitation by conversion of the distal stimulus to a 1:1 response. Temporal variation of the distal stimulus to coincide with different portions of the electrotonic potential demonstrated loss of facilitation when the stimulus preceded, or followed the electrotonic peak voltage.