Twelve-lead electrocardiogram and intracardiac electrograms of the tachycardia.There is no change in atrial activation sequence and no change in AA intervals with interruption of wide complex tachycardia and transition to narrow complex tachycardia at same cycle length (303 ms). Despite the fixed AA intervals, there is a prolongation in HH interval (316 vs 303 ms) at the transition suggesting switch from retrograde His activation from the atriofascicular tract during the wide complex tachycardia (dashed red arrows) to antegrade His activation from atrioventricular (AV) node during narrow complex tachycardia (solid red arrows portraying A and His activation from AV nodal reentry; and green arrows showing the possibility of atrial tachycardia conducting with long AH interval). AA indicates atrio-atrial; AH, atrio-His; HH, His-His; HV, His-ventricular; and VA, ventriculo-atrial.
Illustration of the mechanism of the wide complex tachycardia. The contiguous red line is depicting the atrioventricular nodal reentry tachycardia (AVNRT) circuit. The dashed red line is showing the bystander activation of the ventricle occurring via a right lateral atriofascicular tract resulting in wide QRS complexes. AVNRT is unaffected by termination of antegrade conduction over the accessory pathway because of mechanical trauma from the mapping catheter.