[Role of the autonomic nervous system in the genesis of the electrophysiologic pattern of the double nodal pathway]

Abstract

Thirty-five patients (age: 53 +/- 13 years) with dual A-V nodal pathways pattern were studied following autonomic blockade (propranolol 0.2 mg/kg and atropine 0.04 mg/kg). Six of them had "idionodal" paroxysmal reentrant supraventricular tachycardia. After autonomic blockade the dual A-V nodal pathways pattern remained in 20 patients (57%) and disappeared in 15; however, in the latter, the effective refractory period of the fast pathway decreased significantly and the disappearance of the slow pathway conduction may not have been real since the marked shortening of the fast pathway refractory period may have masked the slow pathway conduction. The longest A2-H2 interval, the effective and functional refractory periods of the fast pathway did not change significantly after autonomic blockade. Even the electrophysiological measures of the slow pathway in the 20 patients in whom they were comparable did not change significantly. The behaviour of the fast and slow pathways measures varied from patient to patient after autonomic blockade. In the 6 patients with idionodal reentrant tachycardia a discrepancy between jump persistence after autonomic blockade and tachycardia induction was observed. These data suggest that: 1) the dual A-V nodal pathways pattern is mainly related to the anatomic structure of the A-V node; 2) the autonomic system affects in a variable way the conduction velocity and the refractoriness of the fast and slow pathways; 3) the dual A-V nodal pathways pattern and the reentry circuit of idional tachycardia imply two different electrophysiological substrata.