An antidromic impulse in an axon refers to conduction opposite of the normal (orthodromic) direction. That is, it refers to conduction along the axon away from the axon terminal(s) and towards the soma.

What determines orthodromic conduction?

Orthodromic denotes the propagation of an impulse along a conduction system (for example, nerve fiber) in the direction it normally travels. ... In the heart, orthodromic refers to an impulse going in the correct direction from the atria to the ventricles, in contrast to some impulses in re-entry.

What is orthodromic and antidromic?

In an orthodromic study, the recording electrodes measure the action potential traveling in the physiologic direction. In an antidromic study, the recording electrodes measure the action potential traveling opposite the physiologic direction.