A "drop" in the atrioventricular conduction curve and dual-pathway electrophysiology.

BACKGROUND

Atrioventricular (AV) conduction time is rate-dependent. As the atrial coupling interval (A1A2) shortens, AV conduction time (A2H2) prolongs. Thus, the AV conduction curve, plotted using A1A2 vs A2H2, is usually "smooth" and "monotonic". A "jump" in the curve is the current clinical criterion of dual-pathway electrophysiology, whereas a "gap" in the curve has also been described.

OBJECTIVE

This study described a new phenomenon, a "drop" in the AV conduction curve. The potential relationship between a drop in the AV conduction curve and the dual-pathway electrophysiology was also examined.

METHODS

Overall, 81 experimental records from rabbit AV nodal preparations containing the following data were analyzed: (1) had at least 1 AV conduction curve and (2) had a recording of His electrogram alternans (a validated new index of dual-pathway conduction). Most cases had intracellular action potential recordings from the AV nodal fibers.

RESULTS

Of the 81 preparations, 3 (3.7%) showed a drop in the AV conduction curve. The drops (at A1A2 = 115 ± 35 ms) always occurred after fast pathway to slow pathway (SP) transition (at 148 ± 7 ms). The drops showed an SP-fast pathway pattern in 2 of the 3 preparations and an SP-SP pattern in the remaining 1 preparation. The drops were associated with and most likely caused by the formation of intranodal/nodal-atrial reentry and its subsequent conduction.

CONCLUSION

A new phenomenon, a drop in the AV conduction curve, has been demonstrated in this study. A drop is likely caused by the formation of intranodal/nodal-atrial reentry and its subsequent conduction.