Dissociation of atrial electrograms by right and left atrial pacing in patients with atrioventricular reciprocating tachycardia.

Seventeen patients had atrioventricular (AV) reciprocating tachycardia incorporating an AV bypass tract as the retrograde limb of the tachycardia circuit. High right atrial pacing during tachycardia dissociated the low septal right atrial electrogram in four of seven patients with a left free wall bypass tract, neither of two patients with a right free wall bypass tract, four of six patients with a posteroseptal bypass tract and both patients with an anteroseptal bypass tract. Pacing from the coronary sinus during tachycardia dissociated the atrial electrogram recorded at the os of the coronary sinus in no patient with a left free wall bypass tract, both patients with a right free wall bypass tract, two patients with a posteroseptal bypass tract and one patient with an anteroseptal bypass tract. These findings suggest two distinct inputs to the AV node, with the left-sided input being part of the tachycardia circuit in patients with a left free wall bypass tract and the right-sided input being part of the tachycardia circuit in patients with a right free wall bypass tract. However, in some patients with a septal bypass tract, neither the right- nor the left-sided atrial input appears to be a necessary link in the tachycardia circuit.