Reciprocating tachycardia which occurs in patients with a preexcitation syndrome (PS) generally is directly related to the presence of the accessory pathway (AP) and is called atrioventricular re-entrant tachycardia (AVRT). The purpose of the study was to evaluate the incidence of re-entrant tachycardia of other nature among patients with a PS.

785 patients with paroxysmal tachycardia were admitted AP ablation, 294 patients with a concealed AP (group I) and 491 patients with a Wolff-Parkinson-White syndrome (WPW) (group II). Programmed atrial stimulation was performed in the control state and if necessary after isoproterenol to induce the clinical tachycardia and determine its mechanism.

AVRT was induced in 760 patients (97%), 282 of group I (96%)and 478 of group II (97%) (NS). Atrioventricular nodal re-entrant tachycardia (AVNRT) was induced in 13 group I patients (4.6%) and 12 group II patients(2.5%) (NS; 0.11). In 9 group I patients (3%) and in 4 group II patients (1%) (p<0.015), both AVRT and AVNRT were induced. In patients with only induced AVNRT, slow pathway ablation was performed and accessory pathway was respected because there was no inducible tachycardia using AP and the conduction over AP was poor. These patients remained free of symptoms after ablation of AV node slow pathway. Among this population 3 families were identified as having either AVRT or AVNRT.

In patients with concealed or patent accessory pathway and complaining of paroxysmal tachycardia, a careful evaluation of the mechanism of tachycardia is required before ablation. Patients with concealed conduction over an AP have more frequently an association of AVRT and AVNRT than patients with a patent preexcitation syndrome. Rarely AVNRT can be the only mechanism of symptoms.