AJP - Heart and Circulatory Physiology, Vol 243, Issue 1 41-H50, Copyright © 1982 by American Physiological Society
Structure and function of specific regions in the canine atrioventricular node
W. T. Woods, L. Sherf and T. N. James
The functional subregions of the rabbit atrioventricular (AV) node have
been examined in detail, but it has not been possible to subject the normal
canine AV node to such rigorous scrutiny. Arterial perfusion and beveled
microelectrodes have now allowed us to explore the anatomic and functional
regions of the isolated canine AV node. The atria and AV junctional tissues
of 20 young dogs were excised and selectively perfused with physiological
solution through the nutrient arteries to the sinus node, AV node, and His
bundle. AV node action potentials had shapes similar to those of the rabbit
AV node and were conducted slowly (56 +/- 7 mm/s); slowest conduction (16
+/- 14 mm/s) was observed in the distal AV node where diastolic
depolarization was always recorded and where maximum upstroke velocity of
the action potential was slowest. From subsequent anatomic studies of the
same preparations we found that the proximal region of the canine AV node
was predominantly composed of interwoven slender transitional cells and
that the distal region contained bundles of transitional cells and small
but conspicuous aggregations of P-cells. The proximal portion of the canine
AV node appeared to be organized for triage of atrial input during sinus
rhythm. Electron microscopic examinations revealed numerous relatively long
(greater than 1.0 micrometers) gap junctions between proximal AV node
cells. The large gap junctions may provide an anatomic basis for
electrotonic interaction during summation and conduction of AV node inputs.
The distal AV node is the site of slowest AV conduction and also where most
forms of AV junctional rhythm originate.
