Key result
In rabbit AV node preparations, facilitation was demonstrated using the H2-S3 format (P<0.001), reflecting inherent cycle-length-dependent properties rather than enhanced dromotropic function.
p-value: p=<0.001
AV nodal facilitation is based on inherent cycle-length-dependent properties of the AV node rather than directly enhanced dromotropic function.
AV nodal facilitation reflects cycle-length dependence rather than enhanced dromotropy; leaves open translation to human physiology.
The phenomenon of atrioventricular (AV) nodal "facilitation," described in traditional "black box"-functional studies, implies enhanced AV nodal dromotropic function. We investigated the role of atrial prematurities in the modulation of the nodal cellular responses in the mechanism of AV nodal facilitation. Atrial and His (H) bundle electrograms and microelectrode recordings from proximal AV nodal cells were analyzed in 15 superfused rabbit AV node preparations. The pacing protocol consisted of 30 basic beats (S1; coupling interval S1-S1 = 300 ms) followed by a facilitating prematurity (S2; coupling intervals S1-S2 of 300, 200, 150, and 130 ms) followed by the test beat (S3; coupling interval S2-S3 scanned in 5-ms steps). Conduction curves (S2-H2 vs. S1-S2, S3-H3 vs. S2-S3, and S3-H3 vs. H2-S3) were constructed. Facilitation (i.e., shortening of S3-H3 when S1-S2 was shortened) was demonstrated in all preparations using the H2-S3 (P < 0.001) but not the S2-S3 format. Microelectrode recordings revealed a causal relationship between the improved proximal AV nodal cellular responses in facilitation and the prolonged S2-S3 interval. There was no evidence for enhanced nodal dromotropic function directly resulting from the introduction of the facilitating beats. Thus facilitation is based on inherent cycle-length-dependent properties of the AV node during application of a complex pacing protocol and primarily reflects the uncontrolled modulation of the proximal cellular response.
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Mazgalev et al. (1997) studied Atrioventricular nodal facilitation (n=15). Pacing protocol with facilitating prematurity vs. Different coupling intervals was evaluated on Facilitation (shortening of S3-H3 when S1-S2 was shortened) (p=<0.001). In rabbit AV node preparations, facilitation was demonstrated using the H2-S3 format (P<0.001), reflecting inherent cycle-length-dependent properties rather than enhanced dromotropic function.
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