[Pharmacologic complications of the unequal reactivity of constituent elements of the myocardium to the parasympathetic system].

Pharmacological consequences of the unequal reactivity of the myocardial different parts to parasympathic system. The effects of acetylcholine on the various levels of cardiac automatism are studied on open chest dogs with extracorporeal circulation. This drug depresses the sinus node, and more specially the atrio-ventricular node (AV node), but does not alter the His bundle and the Purkinje fibers activity. The sensitivity of the intra-cardiac conduction to acetylcholine also depends upon the considered level of conduction: measured with a bipolar electrode situated upon the His bundle, this one is lowered electively in the atrio-ventricular part. So, the A, V. node can be considered as the elective place of action of acetylcholine on the double point of view of automatism and conduction. Drugs modifying the vagal tonus see their action altered, either in a plus way (antiarrhythmic agents), either in a minus way (cardiac glycosides, halogenated hydrocarbons).