Linking phenomenon in dual atrioventricular nodal pathways.

The linking phenomenon is an electrophysiological phenomenon of conduction between 2 different pathways, such as bundle branches, atrioventricular node (AVN) and accessory pathways. The present study used electrophysiological studies to investigate this phenomenon in 14 patients with dual AVN pathways. Decremental ramp pacing at intervals of 10 ms was carried out in high right atrium until the atrio-His (A-H) interval was abruptly prolonged (onset), then subsequent incremental ramp pacing at intervals of 10 ms proceeded until the A-H interval abruptly shortened (offset). The linking window (LW) was defined as the difference between the paced cycle lengths of the offset and the onset. The linking phenomenon occurred in 9 patients (64%). The onset depended on the functional refractory period of the fast pathway and once the linking was established in the dual pathways, the LW was related to the difference between the A-H interval immediately before and after the restoration of anterograde fast pathway conduction. These findings suggest that the linking phenomenon in dual AVN pathways occurs because of anterograde conduction block in the fast pathway and the subsequent concealed retrograde conduction of impulses propagated from the slow pathway.