Morphology and electrophysiology of the mammalian atrioventricular node

Abstract

The AV node of those mammalian species in which it has been thoroughly investigated (rabbit, ferret, and humans) consists of various cell types: transitional cells, midnodal (or typical nodal cells), lower nodal cells, and cells of the AV bundle. There are at least two inputs to the AV node, a posterior one via the crista terminalis and an anterior one via the interatrial septum, where atrial fibers gradually merge with transitional cells. The role of a possible third input from the left atrium has not been investigated. Since the transition from atrial fibers to nodal fibers is gradual, it is very difficult to define the "beginning" of the AV node, and gross measurements of AV nodal length may be misleading. Histologically, the "end" of the AV node is equally difficult to define. At the site where macroscopically the AV node ends, at the point where the AV bundle penetrates into the membranous septum, typical nodal cells intermingle with His bundle cells. A conspicuous feature, found in all species studied, is the paucity of junctional complexes, most marked in the midnodal area. The functional counterpart of this is an increased coupling resistance between nodal cells. An electrophysiological classification of the AV nodal area, based on transmembrane action potential characteristics during various imposed atrial rhythms (rapid pacing, trains of premature impulses), into AN (including ANCO and ANL), N, and NH zones has been described by various authors for the rabbit heart. In those studies in which activation patterns, transmembrane potential characteristics, and histology have been compared, a good correlation has been found between AN and transitional cells, N cells and the area where transitional cells and cells of the beginning of the AV bundle merge with midnodal cells, and NH cells and cells of the AV bundle. Dead-end pathways correspond to the posterior extension of the bundle of lower nodal cells and to anterior overlay fibers. During propagation of a normal sinus beat, activation of the AN zone accounts for at least 25% of conduction time from atrium to His bundle, the small N zone being the main source of AV nodal delay. Cycle length-dependent conduction delay is localized in the N zone. Conduction block of premature atrial impulses can occur both in the N zone and in the AN zone, depending on the degree of prematurity. Several factors determining AV nodal conduction delay have been identified.(ABSTRACT TRUNCATED AT 400 WORDS)

Reentrant Circuits in the Canine Atrioventricular Node During Atrial and Ventricular Echoes

“…Later, combined histological and electrophysiological studies described a zone of transitional cells bordering the compact AV node. 8,9 In the present study, direct recording of AV nodal electrograms and correlation with histology show that AV nodal reentry occurs in this complex network of nodal and transitional cells and in the rim of surrounding atrial cells. McGuire et al 23 found that atrial cells contiguous with the AV node reveal nodal-type electrophysiology.…”

“…However, morphological, electrophysiological, and clinical observations suggest that the AV node includes both of the cell groups that determine its functional properties, namely, transitional and compact nodal cells. 8,9 We recently showed that in canine hearts, reentry during ventricular echoes is confined to the AV node. 10 The underlying mechanisms of unidirectional conduction block and slow conduction are also controversial.…”

Electrophysiological Delineation of the Tachycardia Circuit in Atrioventricular Nodal Reentrant Tachycardia

“…An experimental study has demonstrated that AV nodal conduction is determined by discrete anteroseptal and posteroseptal atrionodal inputs that are associated with differential functional properties. 24 Clinically, Markowitz et al 25 suggested that successful slow pathway ablation is achieved by selective ablation of the posterior atrionodal input.…”

Patient with Atrioventricular Node Reentrant Tachycardia with Eccentric Retrograde Left-sided Activation. Treatment with Radiofrequency Catheter Ablation.

“…12,13) However, it has been reported that multiple AV nodal pathways exist in some patients, and that some of them are located in the deeper layers of the atrial septum, and are connected to perinodal atrial tissues. [5][6][7] In some cases with such connection, especially to the left atrium, it is likely that atypical AVNRT is induced by eccentric retrograde left-sided activation. 8,10,14) In the present electrophysiologic study, double observations of the jump-up phenomenon suggest that triple AV nodal pathways are present.…”

“…4) It has recently been reported that multiple AV nodal pathways exist in patients with the atypical type of AVNRT, and that some of the pathways are located in the deeper layers connected to perinodal atrial tissues. [5][6][7] Hwang, et al have reported that AVNRT with left-sided activation, which may occur with such a connection, is relatively rare. 8) In this report, we describe a patient with AVNRT caused by a left-sided pathway that was confirmed by the success of radiofrequency catheter ablation.…”