Mexiletine as an adjunctive therapy to amiodarone reduces the frequency of ventricular tachyarrhythmia events in patients with an implantable defibrillator.

The most effective pharmacological management of frequent ventricular tachyarrhythmia events in patients with an implantable defibrillator who failed or did not tolerate amiodarone is unknown. The aim of this retrospective cohort study was to assess the efficacy and tolerability of mexiletine in such patients. The patients served as self-controls. The number of treated ventricular tachyarrhythmia episodes (primary outcome); mortality, shocks from the defibrillator, and electrical storm events (secondary outcomes) during mexiletine therapy was compared with a matched duration of observation just before initiating mexiletine in 29 patients who were treated with a median dose of 300 mg/d of mexiletine and were followed for a median of 12 months. None of the patients had to stop mexiletine due to side effect. There was a significant reduction in the incidence of ventricular tachycardia/fibrillation episodes (median 2 vs. 12 events, P = 0.001) and shocks (median 0 vs. 2 events, P = 0.003) in the first 3 months of treatment, but long-term efficacy was only observed among patients who continued amiodarone therapy. In conclusion, mexiletine, when added to amiodarone in case of amiodarone inefficacy, reduces ventricular tachycardia/fibrillation events and appropriate therapies in patients with an implantable cardioverter defibrillator. A randomized trial should validate the efficacy and safety of mexiletine as an adjunctive therapy to amiodarone.