Antiarrhythmic Drugs in Patients with Implantable Cardioverter-Defibrillators

Abstract

Antiarrhythmic drugs need to be initiated in up to 70% of patients with implantable cardioverter-defibrillators (ICDs) in order to treat atrial tachyarrhythmias, decrease the frequency of defibrillator shocks, and terminate ventricular arrhythmias along with antitachycardia pacing. trial fibrillation (AF) occurs in about 20% of patients with ICDs (the majority with congestive heart failure [CHF]). Antiarrhythmic drugs are initiated for this indication in 2-20% of the ICD population. Data from CHF-STAT (Congestive Heart Failure: Survival Trial of Antiarrhythmic Therapy; amiodarone vs placebo) and DIAMOND-AF (Danish Investigations of Arrhythmia and Mortality ON Dofetilide--rial Fibrillation; dofetilide vs placebo) support the approach that restoration and maintenance of sinus rhythm might be beneficial in CHF, even though no study has specifically addressed the CHF population with ICDs. Further clarification on potential benefits of rhythm control in CHF-associated AF will come from the AF-CHF (Atrial Fibrillation and Congestive Heart Failure) trial that is currently underway. The vast majority of patients with ICDs will have discharges of their devices during follow-up. Although class III antiarrhythmic drugs are widely considered to be effective for prophylaxis against frequent shocks, there are surprisingly few controlled studies that demonstrate this. In contrast to conflicting amiodarone data, sotalol has been found to be effective in preventing shocks from ICDs in prospective, randomized, placebo-controlled studies. A large study (SHIELD; SHock Inhibition Evaluation with azimiLiDe) has shown that azimilide significantly reduces ventricular tachyarrhythmia recurrence, thereby reducing the burden of symptomatic ventricular tachyarrhythmia. Other novel antiarrhythmic drugs, such as dofetilide or dronedarone, as well as different strategies (e.g. in the OPTIC [Optimal Pharmacological Therapy in Implantable Cardioverter] trial; beta-adrenoceptor antagonist therapy alone, amiodarone plus beta-adrenoceptor antagonist therapy, or sotalol alone) for the prevention of ICD shocks are under evaluation. The majority of antiarrhythmic drugs, including sotalol, dofetilide, and azimilide, have no effect on, or are even associated with a decrease in, defibrillation thresholds in humans. Amiodarone, in contrast, has been shown to be related to higher defibrillation thresholds at implant and during follow-up of monophasic devices. Potential cardiac (e.g. ventricular proarrhythmia, negative inotropic effect) and drug-specific non-cardiac adverse effects are a frequent cause for drug discontinuation and need to be considered when initiating and maintaining antiarrhythmic drug therapy. In conclusion, antiarrhythmic drugs are frequently used in ICD patients, the main indications being treatment of atrial tachyarrhythmias and prevention of ICD shocks. Despite potential adverse effects, antiarrhythmics can be administered safely, as long as ICD/drug interactions are appreciated. Controlled studies that will further define the role of concomitant antiarrhythmic drug utilization in patients with ICDs are underway.