Microelectrode study of Wenckebach periodicity in canine Purkinje fibers |
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Authors: | J R Wennemark J P Bandura |
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Institution: | From the Department of Medicine, Division of Circulatory Diseases, University of Tennessee College of Medicine, Memphis, Tenn., USA |
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Abstract: | Electrophysiologic mechanisms responsible for Wenckebach periodicity produced experimentally in a segment of blocked canine Purkinje fibers were investigated with multiple microelectrode recordings. Transmission through the zone of block was electrotonic. The Wenckebach mechanism was related to a progressive decrease in the efficacy of the transmitted electrotonic potential as a stimulus for the regenerative response at the distal block boundary with successive impulses of the cycle. This was manifested in the transmembrane potentials as a progressive decrease in upstroke velocity and a voltage change that caused the electrotonic potential to become progressively removed from the threshold for stimulation. The immediate cause of this phenomenon was a progressive increase in the voltage level (more negative) from which the electrotonic potential originated and a resulting change in voltage-dependent membrane resistance that further attenuated the signal with successive impulses of the cycle.Two main mechanisms appeared to be responsible for these phenomena: (1) a progressive increase in maximal repolarization voltage (more negative) of the transmembrane potential, and (2) a progressive decrease in the diastolic interval that, in the presence of enhanced phase 4 diastolic depolarization, caused the voltage level from which the electrotonic potential originated to become further removed from the stimulation threshold with successive impulses of the cycle. |
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Keywords: | Address for reprints: James R Wennemark MD Division of Circulatory Diseases Department of Medicine University of Tennessee College of Medicine 951 Court Ave Room 353D Memphis Tenn 38103 |
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