Initiation of atrioventricular nodal reentrant tachycardia in patients with discontinuous anterograde atrioventricular nodal conduction curves with and without documented supraventricular tachycardia: observations on the role of a discontinuous retrograde conduction curve.

To evaluate factors playing a role in initiation of atrioventricular (AV) nodal reentrant tachycardia utilizing anterogradely a slow and retrogradely a fast conducting AV nodal pathway, 38 patients having no accessory pathways and showing discontinuous anterograde AV nodal conduction curves during atrial stimulation were studied. Twenty-two patients (group A) underwent an electrophysiologic investigation because of recurrent paroxysmal supraventricular tachycardia (SVT) that had been electrocardiographically documented before the study. Sixteen patients (group B) underwent the study because of a history of palpitations (15 patients) or recurrent ventricular tachycardia (one patient); in none of them had SVT ever been electrocardiographically documented before the investigation. Twenty-one of the 22 patients of group A demonstrated continuous retrograde conduction curves during ventricular stimulation. In 20 tachycardia was initiated by either a single atrial premature beat (18 patients) or by two atrial premature beats. Fifteen of the 16 patients of group B had discontinuous retrograde conduction curves during ventricular stimulation, with a long refractory period of their retrograde fast pathway. Tachycardia was initiated by multiple atrial premature beats in one patient. Thirteen out of the remaining 15 patients received atropine. Thereafter tachycardia could be initiated in three patients by a single atrial premature beat, by two atrial premature beats in one patient, and by incremental atrial pacing in another patient. In the remaining eight patients tachycardia could not be initiated. Our observations indicate that the pattern of ventriculoatrial conduction found during ventricular stimulation is a marker for ease of initiation of AV nodal tachycardia in patients with discontinuous anterograde AV nodal conduction curves.