Jun 1, 1997

Mechanism of atrioventricular nodal facilitation in the rabbit heart: role of the distal AV node

The American Journal of Physiology
G J FahyT Mazgalev

Abstract

We investigated whether atrioventricular (AV) nodal facilitation is the result of distal AV nodal action potential shortening. Atrial and bundle of His (H) electrograms and microelectrode recordings from proximal and distal AV nodal cells were analyzed in eight superfused rabbit AV node preparations in response to two pacing protocols. In the facilitation protocol, an atrial extrastimulus (A3) was preceded by an atrial impulse (A2) introduced 300, 200, 150, or 125 ms after 30 basic beats (A1). The preexcitation protocol differed from the facilitation protocol by the addition of a premature His depolarization (h2) such that the H1-h2 interval was shorter than the H1-H2 interval. Conduction curves (A3-H3 vs. H2-A3, h2-A3, and A2-A3 intervals) were constructed. Facilitation was demonstrated in all preparations when H2-A3 was used (P = 0.02) but not in the A2-A3 format. Compared with facilitation at the same A1-A2 intervals, preexcitation, despite shortening the distal cellular action potential duration, resulted in longer A3-H3 delays (P = 0.002), shorter A2-A3 intervals, and depression of the proximal nodal cellular response. Thus facilitation does not result from altered distal AV nodal characteristics and instead is a manifesta...Continue Reading

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Mentioned in this Paper

Microelectrodes
Reaction Time
Action Potentials
Chinchilla Rabbits
Cardiac Conduction System
Structure of Atrioventricular Node
Electrophysiology (Science)
NODAL gene
Bundle of His
Heart

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