Atrioventricular reentrant tachycardia occurs when a reentrant circuit is present outside of the AV node through an abnormal conduction pathway that connects the atrium to the ventricles.

If pacing continues at the pacing site at a constant rate, a little faster than the tachycardia ... constant and each orthodromic wavefront propagates all the way along the reentrant circuit.

In the case of reentrant circuits ... usually called orthodromic and antidromic, according to whether they proceed in the same or the opposite direction as during tachycardia.