[The influence of frequency and blockade of the autonomic nervous system on the functional behaviour of the human conduction system. Part A: Conduction velocity (author's transl)].

32 patients were studied by His-bundle recordings to examine the extent to which frequency and autonomic nervous system influence the conduction velocity in the subdivisions (atrium, AV-node, His-Purkinje system) of the normal PR-interval. The measurements were performed during sinus rhythm and three electrically induced atrial frequencies before and after intravenous administration of 1 mg Atropine (15 patients) and 0.4 mg Visken (17 patients). In influencing the atrial conduction velocity frequency dominates the blockade of both components of the autonomic nervous system. Increase in frequency lengthens the intraatrial conduction time. Blockade of parasympathicus and sympathicus does not significantly influence the changes in intraatrial conduction velocity induced by increase of frequency. Patients with prolonged intraatrial conduction respond in the same way to cycle length shortening and blockade of the autonomic tone as patients with normal conduction. The results are discussed with respect to acetylcholine and catecholamine influence on the electrophysiological properties of the atrial myocardium. The AV-node is the part of the conduction system most sensitive to the influence of both cycle length shortening and blockade of the autonomic nervous system. Artificially induced cycle length shortening prolongs the intranodal conduction time to a different individual level for each patient. Blockade of the parasympathicus not only shortens this interval but also reduces the steepness of the AH-time induced by atrial pacing. Blockade of the sympathicus has the opposite effect. The most likely explanation for these results is the abolishing of the functional dissociation within the AV-node by blocking the autonomic influence on this structure. The conduction velocity in the His-Purkinje system is influenced neither by atrial pacing nor by blockade of both components of the autonomic nervous system.