Reciprocal beats initiated by artificial pacemaker.

In conclusion, the underlying mechanism for this rhythm disturbance in our patient is the re-entry phenomenon, which is dependent upon a localized unidirectional block in the A-V junction. The predisposing factors, including digoxin and Inderal which tend to prolong A-V conduction, are considered for the mechanism of the production of the reciprocal beats in our case. Upon temporary withdrawal of digoxin and Inderal, the re-entry phenomenon has disappeared.