Concealed Conduction

The existence of concealed conduction of atrial beats has been demonstrated. Concealed conduction within the atrioventricular node has been studied by recording the transmembrane potential of single nodal fibers. Conduction block in this part of the specialized conducting system depends more upon decremental conduction within certain nodal fibers than upon differences in action-potential duration. Also, the extreme delay of activation that results from such decremental conduction explains certain changes in atrioventricular delay associated with premature atrial beats as well as a prolonged refractoriness of atrioventricular transmission after concealed nodal conduction of an atrial extrasystole. In the in situ dog heart, local bipolar electrograms recorded from various parts of the bundle of His, bundle branches, and peripheral Purkinje fibers have shown that con cealed conduction may extend through the atrioventricular node and the bundle of His and that block may occur between common bundle and bundle branches or between the latter and the peripheral Purkinje fiber. Block in these locations, which results from local differences in the action-potential duration, has been compared to decremental conduction within the atrioventricular node.