[Mexiletine: electrophysiologic effects].

A complete electrophysiological evaluation has been performed before and after the intravenous administration of Mexiletine (M.) (3 mg/Kg/B.W. in 5 minutes) in 28 patients (pts) (6 pts with normal conduction system, 4 pts with sick sinus syndrome, 5 pts with intranodal AV block, 13 pts with bundle branch block, of which 4 with pathological HV and 1 with intrahisian conduction defect). With the exception of a shortening of QTc interval in all the pts, the drug did not significantly affect any other electrophysiological parameters. In the patient with intrahisian conduction defect, M. prolonged the H1 - H2 interval. A statistically significant increase of heart rate has been also observed in a second group of 8 pts with normal sinus function, in whom M. administration was preceded by Atropine (I.V. bolus 0,04 mg/Kg/B.W.). This finding seems to exclude a vagolytic effect of M. The conclusions derived from our experience and pertinent literature are the following: M. is not useful in the treatment of supraventricular arrhythmias because it has negligible effects on atrial and AV nodal conduction; the drug may be safely employed in the treatment of ventricular arrhythmias in pts with atrial and/or AV nodal conduction defects; special caution must be employed when the drug is utilized in pts with sick sinus syndrome and/or with marked intraventricular conduction defects.