Interactions between drugs and devices: experimental and clinical studies.

It is important to understand the potential interactions between the implantable cardioverter defibrillator (ICD) and antiarrhythmic therapy in patients who receive pharmacologic therapy as an adjunct to ICD therapy. In our cohort of 101 patients, antiarrhythmic agents were prescribed in 67% of the patients during long-term therapy for the following reasons: to suppress ventricular tachycardia/ventricular fibrillation episodes (50%), to lower the rate of ventricular tachycardia (19%), to prevent supraventricular tachyarrhythmia (21%), and for other reasons (10%). The potential influence of antiarrhythmic drugs on the defibrillation threshold (DFT) is the most important issue. In animal studies lidocaine increased the DFT in a dose-dependent manner. Quinidine, procainamide, propafenone, and flecainide did not affect the DFT or, in some cases, led to a small increase. Sotalol even decreased the energy requirements for internal defibrillation. In a prospective investigation we were able to document a significant increase of DFT (from 14.1 + 3.0 to 20.9 + 5.4 J, p < 0.001) by the use of amiodarone (400 mg/day), whereas this effect was not found in patients who received mexiletine (720 mg/day). In conclusion, the DFT or the safety margin for defibrillation should be known before antiarrhythmic agents are administered to patients with an ICD. In case of a small safety margin, the DFT should be reassessed after antiarrhythmic drug therapy is begun.