[Studies on the Effect of Melixetin (Kö 1173) on AV-conduction Time and Sinus Pulse Automation in Persons with Healthy Hearts and in Patients with Disorders of the Impulse-conduction System]

The influence of Mexiletine on the av-conduction time and sinus node recovery time of 24 patients with and without disturbance of impulse formation and conduction was examined. There was no change of conduction time proximal to the His-bundle. Four patients developed block distal to the His-bundle, 3 of which had a conduction disturbance before application of the drug consisting in 2:1 av-block or bifascicular block. Two patients with WPW-syndrome showed no change of impulse conduction. Five out of 12 patients showed an increase of the effective recovery period. Three out of 15 patients showed an increase of threshold potential from 0.35 to 0.7 volt with suppression of escape rhythm. The sinus node recovery time was prolonged in 2 out of 9 patients, one of which had a sick sinus syndrome. As there seems to be some influence of Mexiletine on sinus node impulse formation and the impulse conduction distal to the His-bundle, this drug probably should be used with caution in patients with disturbance of automaticity and distal av-conduction.