[Electrophysiological study of cardiac effects of succinylcholine: role of vagal tone and hyperkalemia in anesthetized dog (author's transl)].

The effects of intravenously infused succinylcholine (SCh): 1 mg/kg/minute during 30 minutes were assessed in anesthetized dogs on spontaneous heart rate, conduction within the atrio-ventricular node and the His-Purkinje system and on atrial (AERP) and atrio-ventricular (AVERP) effective refractory periods with varying levels of vagal tone and under mild hyperkalemia. 1) The heart rate which was not affected by SCh in the absence of vagal tone was by contrast increased by 50 p. cent when vagal tone was maintained. Under hyperkalemia, the vagolysis-mediated tachycardia did not prove more marked. 2) The conduction velocity, which was never modified by SCh in either the atria or the His-Purkinje system, was always accelerated with vagal tone. This acceleration is directly related to the vagolytic properties of SCh, but also partly to a mild hyperkalemia. The changes of potassium blood levels tend to reverse the potassium outflow due to the parasympathetic neuromediator. 3) The AERP was was lengthened by SCh and hyperkalemia; the latter impaired the outflow of potassium ions responsible for repolarization. The AVERP was always shortened when the vagal tone is maintained, however less largely under mild hyperkalemia which limits SCh anticholinergic effect owing to its own anticholinergic action.