Does the atrioventricular node conduct?

Abstract

It is difficult to be certain wh en the term "conduction" was first applied to the transfer of atrial activation to the ventricles .' In 1894, Engelmann used the word "Leitung", which can be translated as "connection" or as "conduction" .2 In 1906, Tawara described the atrioventricular node, which he termed "Das Reizleitungssystem des Herzens ".' The mechanism of atrioventricular transmission continued to be a subject of considerable debate.4.9 There is a summary of the various mechanisms that were thought to explain atrioventricular transmission in Scherf and Cohen's book on the atrioventricular node.'o Primarily through the work of Hoffman and Cranefield and their associates,"12 and to a les ser extent others,13 14 it became generally accepted that atrial excitation was slowly "conducted" through the atrioventricular node to the His-Purkinje system and the ventricular myocardium. Hoffman and Cranefield stated that "the excitable cell . . . possesses the same electrical properties as a telegraph cabie" . 15 Because the "connecting" tissue between the atria and the ventric1es was regarded as a series of excitable cells, it followed that the atrioventricular junction was a conduction system. None the less, studies of the complicated structure of the mammalian atrioventricular junction,14 and the time relation between recorded action potentials from exposed rabbit atrioventricular nodel6 17 have not as yet yielded sufficient data to construct a model of the spatial excitation of the atrioventricular node that is analogous to that of the canine and human ventric1es .18 19 The atrioventricular node cannot be mapped with the preciseness required to document the sequence of excitation through this part of the specialised conduction system. Although it seems logical to assume conduction through the atrioventricular node, this claim remains open to question and conjecture. Moreover, some observations20 sugge st that the traditional concept of the atrioventricular junction as a passive cable with varying electrical properties warrants further examination.