[Tachycardias caused by double ventricular responses and unusual atrioventrio-ventricular relations in linear dissociation of the AV node].

Noninvasive recordings in a 69-year-old woman showed phasic shifts between two distinct PR intervals of about 0.21 and 0.58 s suggestive of dual AV nodal conduction in the presence of two intranodal pathways. Episodes of tachycardia exhibited a one to two relationship between P waves and QRS complexes, with the same short and long PR intervals interpreted as simultaneous anterograde fast and slow conduction via the two AV nodal pathways, leading to a double ventricular response to single P waves. Various mechanisms of transition from short to long or long to short conduction times and concealed conduction phenomena could be demonstrated supporting the concept of two functionally separated intranodal pathways.