- CRYSTAL, E., et al.: Mexiletine Related Chronic Defibrillation Threshold Elevation: Case Report and Review of the Literature. Many antiarrhythmic drugs may produce a rise in defibrillation threshold. Mexiletine is a frequently used antiarrhythmic drug in patients with an implantable cardioverter defibrillator, usually thought of as producing no or minimal effects on the defibrillation threshold. The current case report presents a patient with an endocardial implantable cardioverter defibrillator being treated with mexiletine, which precluded the ability to defibrillate the patient.