PubMed2002
The existence of a single atrio-ventricular fascicle had been suggested in the 19th century by Wilhelm His junior. In 1906, Sunao Tawara described in details the existence of a specific muscular fascicle in charge of the atrio-ventricular conduction. Since, it has remained famous under the name of atrio-ventricular node. It is located in the apical part of the Koch triangle. It is 5 to 7 mm long and 2 to 5 mm wide and includes often an enlargement of its compact portion along the fibrous annulus to the coronary sinus ostium which seems to be associated with the development of a intra- or atrio-nodal re-entry circuit. Its action potentials are qualified as "slow response" and propagate with a speed of 0.02 to 0.05 m/sec (which is comparable to that present in the sinus node). This propagation slowness explains the PR interval on surface EKG tracings and the AH interval in intra-cardiac electrogram. When AV node cells are requested by a rapid atrial rhythm, their physiological response is made under the mode of beatings group described by Luigi Luciani and Karel Wenckebach, prior to the EKG's invention. The atrio-ventricular physiological relationship during the atrial acceleration is made according to the Luciani-Wenckebach mode and then 2/1 mode as described in the non-linear dynamics theory. The most frequent pathological of the nodal conduction are the atrio-ventricular blocks and nodal duality. They are described and commented in this article. The nodal conduction disturbances are currently accessible to different therapeutic patterns such as cardiac pacing or ablative techniques. Nonetheless the innermost mechanism are still incompletely identified and will for sure be a matter of numerous studies in the future.