Observations on Concealed Conduction in Atrial Fibrillation

The mechanism of the ventricular dysrhythmia associated with atrial fibrillation in isolated rabbit heart was studied by recording electrograms from right atrium and ventricle simultaneously with transmembrane action potentials recorded from single fibers within the A-V node and right bundle branch. In most experiments, the variation in ventricular cycle length during experimentally initiated atrial fibrillation resulted from concealed conduction within the A-V node. The most frequently recorded ventricular interval during atrial fibrillation was found when a single response was concealed within the A-V node. In several experiments, as many as seven to nine consecutively concealed responses were recorded from the A-V node. When repetitive A-V nodal concealment occurred, the resulting ventricular cycle lengths were prolonged accordingly. In only a few experiments were conduction delay and block observed within the ventricular specialized conduction system (VSCS) during atrial fibrillation. Subsidiary pacemakers were never observed within the A-V node but were noted occasionally within the VSCS following epinephrine administration. Multiple A-V nodal concealments were usually associated with rapid atrial rates.