Influence of the site of stimulation on atrioventricular nodal refractory periods and the effect of verapamil.
The refractory periods of the atrioventricular (AV) node appear dependent on the pattern of AV nodal input. In 21 superfused AV rabbit heart preparations stimulated from each of the 2 principal input regions, crista terminalis or atrial septum, the effect of changing the site of stimulation of the AV nodal refractoriness and the relative effect of verapamil on AV nodal refractoriness was determined. In 6 of 21 preparations the functional AV refractory curve became discontinuous only when stimulation was applied at the atrial septum and suggested dual AV nodal pathways (dual pathways group). In the 15 other preparations no interruption of the curve occurred with either crista terminalis or atrial septal stimulation (normal conduction group). In the normal conduction group, the difference in the effective refractory period of the AV node obtained by crista terminalis vs atrial septal stimulation was not significant (154 +/- 25 vs 150 +/- 28 ms). However, the functional refractory period was significantly longer with crista terminalis vs atrial septal stimulation (232 +/- 19 vs 239 +/- 19 ms, p less than 0.001). After verapamil administration, the effective and functional refractory periods during crista terminalis vs atrial septal stimulation were prolonged to 270 +/- 49 vs 285 +/- 55 ms (p less than 0.01) and 335 +/- 43 vs 351 +/- 41 ms (p less than 0.001), respectively. Thus, the difference in refractory periods associated with changing the stimulation site was exaggerated with verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)
Iinuma
H
H
Dreifus
L S
LS
Price
R
R
Michelson
E L
EL
D000818:Animals; D016275:Atrial Function; D001283:Atrioventricular Node / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D006329:Heart Conduction System / Q000502:physiology*; D007700:Kinetics; D011817:Rabbits; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology*
D014700:Verapamil