[Slow and fast AV nodal pathways in tachycardia complicating Wolff-Parkinson-White syndrome: report of a case].

Electrophysiologic studies in a patient with intermittent ventricular pre-excitation revealed several types of paroxysmal narrow-QRS tachycardia (PSVT). One type of PSVT was characterized by normal retrograde atrial sequences with P waves occurring simultaneously with QRS. This type of PSVT reflected AV nodal reentry with anterograde slow pathway and retrograde fast pathway conduction. A second PSVT reflected alternation of anterograde fast and slow AV nodal pathway conduction and retrograde anomalous pathway conduction. A third PSVT reflected anterograde slow AV nodal pathway and retrograde anomalous pathway conduction. Moreover, discontinuous AV nodal conduction curves (A1A2/H1H2), characteristic of dual AV nodal pathway conduction, were obtained with programmed atrial extra stimulation. These observations suggest that dual AV nodal pathway conduction can coexist with abnormal bypass tract and can be the cause of PSVT in patients with Wolff-Parkinson-White syndrome.