[Electrophysiological demonstration of more structures in the atrioventricular node (author's transl)].

Three types of atrioventricular nodal conduction curves, relating A1A2 to H1H2, generated with atrial extrastimulus technique, are known. The first type is smooth, suggesting the homogeneous structure of A-V node. The second type, with abrupt increase in H1H2 response over a critical range of A1A2 coupling intervals, suggests the presence of fast and slow A-V nodal pathways. We have found in five patients the third tipe of A-V conduction curve, giving evidence of an intranodal final common pathway, distal to the fast and slow A-V nodal pathways. The thyrd type of curve enables us to know also some alectrophysiological properties of final common pathway. Indeed we have defined effective and functional refractory periods of fast, slow and final common pathways as far as we can in this type of curve. Paced heart rate variations and atropine medications have led the third type of A-V conduction curve to change into the second type in three cases, into first type in one case. These changes of A-V nodal conduction curves are related to different influence of cardiac cycle lenghts and autonomic nervous system on refractory periods and conduction velocity of the outlined intranodal structures

A pharmacological approach to the study of AV conduction in man.

Smooth and interrupted curves of AV conduction, generated with an atrial extrastimulus technique, are seen in man, suggesting the involvement of two physiological AV pathways named "alpha" and "beta" and leading to a final common pathway (FCP). In view of this knowledge, the effects of some representative antiarrhytmic agents (Atropine, Verapamil, Ajmaline) were studied in eight patients in order to elucidate the physiological role of the various components of AV junction. Verapamil decreased conduction velocity of both "alpha" and "beta" pathways and increased their refractoriness; Atropine decreased "alpha" and "beta" pathways' refractory periods and increased their conduction velocity; further studies are required to clarify the effects of Ajmaline on AV conduction