[Clinical electrophysiological evaluation of mexiletine]

We studied sixteen patients (pts), seven men and nine women (mean age 35 years) with sustained tachyarrhythmias, for acute therapeutic trial with mexiletine (3 mg/kg IV). The arrhythmias were: ventricular tachyarrhythmia in eight pts supra-ventricular tachycardia (SVT) in eight pts, seven due to abnormal tracts (43%) and one to nodal reentry. After mexiletine administration, the sinusal cycle length was reduced in 12.7% (P less than 0.05) and the H-V interval decreased 6.1% (P less than 0.05). The nodal conduction (A-H) didn't show any substantial change, neither the atrial nor the ventricular refractory periods (RP). In two pts with complex premature ventricular beats it was not possible to induce the ventricular tachycardia(VT) six had sustained VT. After mexiletine administration, three of them (37.5%) showed self limited VT with a greater R-R cycle. Another case was complicated by ventricular fibrillation, In the pts with SVT, the retrograde RP of the abnormal tracts shortened in 27% (P less than 0.05), while the antegrade was not modified. Mexiletine showed to be efficient for the VT treatment. Its efficacy was very limited in pts with SVT. There was no evidence of any deleterious effect over the His-Purkinje conduction.