[Influence of the autonomic nervous system on the normal and pathological atrioventricular node]

The finding of a first-degree atrioventricular block suggests various mechanisms of atrioventricular (AV) node alteration: organic lesion, or functional disorder related to the autonomic nervous system, or a combination of both. The influence of the autonomic nervous system was evaluated by administration of Jose's regimen, i.e. intravenous injection of propranolol 0.2 mg/kg bodyweight and atropine 0.04 mg/kg bodyweight. This regimen was tested in 101 patients divided into two groups: 38 subjects with normal sinus node and AV node acting as controls, and 63 patients with abnormal AV node. In the control group the autonomic nervous system had no influence on atrio-hisian (AH) conduction time or on the effective refractory period of the AV node under an imposed cycle of 600 ms. Wenckebach's period significantly (p less than 0.01) increased from 352 +/- 40 ms to 376 +/- 47 ms. Parasympathetic activity was found to predominate in the sinus node. In the group with pathological AV node three types of response were observed after pharmacological inhibition of the autonomic nervous system: (a) improvement or even complete normalization (40%) of AV node conduction ability (AH, Wenckebach's period) suggesting vagal hyperactivity, as also found in the sinus node; (b) changes similar to those observed in the control group and reflecting the same behaviour of the autonomic nervous system, and (c) increase in AH conduction abnormalities reflecting the presence of a sympathetic overdrive tending to minimize the consequences of an atrioventricular organic lesion. This sympathetic overdrive was also found to be present in the sinus node.