Microelectrode Study of Delayed Conduction in the Canine Right Bundle Branch

1968 Circulation Research  
The electrophysiology of conduction delay was investigated in the semiisolated right bundle branch of 30 large mongrel dogs. Delay was produced by the external application of an electric blocking current to the bundle branch. Multiple recordings with glass capillary microelectrodes revealed two basic deflections associated with the delay phenomenon. An initial, or leading, deflection originated from the proximal or leading edge of the block and was rapidly transmitted through the block with
more » ... the block with progressive decay of voltage and rise velocity. A second, or trailing, deflection originated from the regenerative response at the distal or trailing edge of the block and was rapidly transmitted retrograde into the block, with progressive decay of voltage and rise velocity. The transmitted potentials appeared to be electrotonic in nature. The leading deflection appeared to be the transmitted event which maintained a conduction ratio of 1:1 through the block. The magnitude of delay was then related to the time required for this deflection to reach the threshold potential and initiate a regenerative response in the trailing portion of the block where the cells were Jess affected by the blocking current. ADDITIONAL KEY WORDS electric blocking current electrophysiology partial block mechanism of block incomplete bundle-branch block Research, Volume XXI11, December 1968 753 by guest on August 12, 2017 http://circres.ahajournals.org/ Downloaded from 754 WENNEMARK, RUESTA, BRODY FIGURE 1 Top: The right bundle branch has been stained with Lugol's solution (arrows). S p , proximal bipolar stimulating electrode; S a , distal bipolar stimulating electrode; E p) proximal unipolar recording electrode; E a , distal unipolar recording electrode; E b , blocking positive electrodes. A centimeter rule was mounted with each preparation. The blocking negative electrode is beneath the preparation and cannot be seen in this view. Bottom: Two areas of block were produced in the right bundle branch, block A (left) and block B (right) (cross hatch). The blocking effect was produced by the more distant negative depolarizing electrode. The two segments of block were separated by a localized area of hyperpolarization (circles) under the positive electrodes (E). meters. The blocking current was delivered to the preparation through small polyethylene tubes which were filled with Tyrode's solution. A silver wire-liquid junction was made distant from the preparation. Two electrodes were symmetrically placed directly over the mid portion of the bundle branch, allowing space for recording between them. These electrodes were connected to the positive pole of the battery. A third electrode, which was somewhat larger, was placed 5 mm
doi:10.1161/01.res.23.6.753 pmid:5727183 fatcat:a5gbndnqtnfevcqf2ncrwi7fdq