Mexiletine: Lack of predictors of clinical response in patients treated for life-threatening tachyarrhythmias

Fifty-one patients with ventricular fibrillation (VF) (13) or clinically documented or induced sustained ventricular tachycardia (VT) (38) were treated with 600-900 mg/day of mexiletine after baseline ECG, Holter monitors, radionuclide ventriculograms, and electrophysiology (EP) tests. Mean ejection fraction (EF) was 33% ± 13% with underlying heart disease being atherosclerotic in 34 (67%), dilated cardiomyopathy in 10 (20%), and hypertensive or valvular in 6 (12%). Previous antiarrhythmic trials consisted of 0 to 6 drugs (mean 2.4). Sustained VT was induced in 31 (mean cycle length 273 msec) and nonsustained VT in 15 (mean cycle length 229 msec). Thirteen patients considered responders (no clinical or induced VT or VF) were discharged on mexiletine with 4 (31%) having VT or VF during follow-up of 12 ± 15 months. Mexiletine response was not predicted by any variable tested. However, 4/13 (31%) of VF patients responded compared to 5/38 (13%) VT patients. Although 8/9 responders had EF > 30%, EF did not statistically predict response for the study group or patients with sustained VT. Four VF responders had a significantly higher EF (48%) than 9 who had recurrence (30%) (p < .05). Therefore, while there are no clinical predictors of response in sustained VT, mexiletine may be more effective in treating VF than sustained VT especially if EF is preserved.