Alterations of orthodromic circus movement tachycardia by dual atrioventricular nodal pathways in a patient with Wolff-Parkinson-White syndrome.

In a patient with a left sided accessory pathway (AP) three different types of orthodromic circus movement tachycardia were observed: (1) narrow QRS complex tachycardia with a stable cycle length (CL); (2) wide QRS complex tachycardia with a functional bundle branch block ipsilateral to the AP, which, paradoxically, had a shorter CL. The decrease in CL was due to a decrease of the AH interval; and (3) narrow QRS complex tachycardia with alternating CL, due to alternations of the AH interval. These phenomena were attributed to a concomitant dual atrioventricular (AV) node, which was eventually proven after successful catheter ablation of the AP.