The Heterogenous Structure of the Specialized Tissue in the Heart as a Factor in Atrioventricular Conduction Delay

Experiments have been done on the A-V conducting fibers of the toad heart and rabbit heart to examine the nature of the A-V conduction.The configuration of the conducted transmembrane action potentials was found to depend on the direction of impulse propagation. However, there was no obvious relation between the rate of rise of the action potential and the distance the impulse had travelled in the A-V conducting pathway.The unique change of shape of the action potential recorded from the atrial margin of the A-V conducting pathway of the toad heart after stimulation of the vagus nerve was not seen when the heart was driven antidromically. Sometimes a summation of action potentials was observed after stimulation of the cardiac nerve.From these results, it is concluded that heterogeneous structure of the A-V conduction systems, as shown by the differential interference microscopy, is responsible for the A-V conduction delay.