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PubMed1983

[Microelectrodes].

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Acetylcholine↗
PubMed1984

[Measured and estimated sinoatrial conduction during variations in rhythm. Microelectrode study of the isolated rabbit atrium].

Strips of isolated atrium were obtained from 10 rabbits to study the validity of indirect methods of estimating sinoatrial conduction time during variations of the sinus rhythm. Direct recordings of the trans-membrane action potential of the sinus node were made. Mapping of the sinus region was undertaken to determine the site of the dominant pacemaker. A quadripolar surface electrode was positioned on the lower part of the crista terminalis for stimulation and recording of the atrial potential. This enabled a comparison to be made between the indirect estimated and the directly measured conduction times. An intrasinusal shift of the dominant pacemaker was obtained by cooling from 38 degrees C to 35 degrees C. This shift occurs progressively in the cranino-candal direction. The estimated and measured conduction times were compared under basal conditions and after cooling. The sinus cycle was significantly longer (p less than 0.001) at 35 degrees C (318 +/- 68 ms) than at 38 degrees C (255 +/- 48 ms). The mean measured anterograde conduction time also decreased from 36 to 31 ms (p less than 0.01) and the mean measured retrograde conduction time also decreased from 39 to 33 ms (p less than 0.02); the total conduction time decreased from 75 to 64 ms (p less than 0.001). The results of the total estimated conduction times were discordant. The associated effects of stimulation and cooling can cause conduction defects and an overestimation of the conduction time.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1984

Comparison of the posterior and anterior activation of the atrioventricular node in rabbit heart with identical prematurity--microelectrode investigation.

The present work evaluates the input prematurity of AVN-activation as a determinant atrioventricular condition. The cellular organization of conduction is studied by consecutive stimulation of the posterior input (crista terminalis) and the anterior input (interatrial septum) with identical prematurity. The results obtained demonstrate the existence of essential differences in conduction upon posterior and anterior stimulation. Above all, separate activation of the two inputs leads to different timing of the cell excitation from the adjacent AN-zones; different sections of the AN-area may prove to be excluded from the conduction process to the His-bundle. Moreover, upon changing the direction of the excitatory wave (even if the prematurity of the extrastimulus is preserved unchanged), temporal and spatial reorganization occurs in the N-zone of the node, the concurrent changes in the shape of the action potentials and the intervals between them. The activation of only one AVN input (by electrical stimulation) could cause passive or active excitation of the other. In the first case the passively activated input may participate in the retrograde conduction of the excitation to the atrium (re-entry); in the second case, under definite conditions, the two antegrade input waves may interact within the AVN. Knowledge only of the absolute values of the stimulation prematurity is not sufficient for description of the conduction through AVN.

Animals↗