Figure 3. Atrial extrastimulus during tachycardia
AES delivered at the high right atrium (HRA 1-2) activating the septal
regions during retrograde fast pathway conduction (i.e. collision with
the retrograde fast pathway impulse) caused block in the slow pathway
terminating the tachycardia. This termination demonstrates that the slow
pathway is a part of the reentrant circuit.