Effects of autonomic blockade on dual atrioventricular nodal pathways pattern

Fifteen patients (age: 57.6±14 years) showing dual A-V nodal pothways pattern during basal electrophysiological testing were studied following pharmacological autonomic blockade (iv propranolol 0.2 mg/Kg and iv atropine 0.04 mg/Kg). After induction of the autonomic blockade, the dual A-V nodal pathways pattern was not present in four patients due to disappearance of the slow pathway; the pattern remained in 11 (73%). The longest A₂-H₂ interval, the effective and functional refractory periods of the fast pathway did not change significantly following autonomic blockade. Even the electrophysiological measures of the slow pathway, in the 11 patients in whom they were comparable, did not change significantly after autonomic blockade. These data suggest that: 1) the dual A-V nodal pathways pattern is mainly related to the intrinsic structure of the A-V node; 2) the autonomic nervous system only affects in a variable way the refractoriness and the conduction velocity in the two pathways.