Effect of drugs on defibrillation capacity

Over 300,000 people die of sudden cardiac death (SCD) in the US annually. Implantable cardioverter-defibrillators (ICDs) have been shown to be more effective than antiarrhythmic drugs for the prevention of SCD in specific susceptible populations. Many patients in whom ICDs have been implanted receive concomitant therapy with antiarrhythmic drugs, for the purpose of reducing the frequency of appropriate and inappropriate defibrillation shocks. Drugs may influence defibrillation capacity and therefore influence the function of ICDs. The objective of this article is to review and update the literature regarding the effects of drugs on defibrillation capacity.A literature search was performed using PubMed (1966 to December 2007) to identify clinical studies, case reports and animal studies describing the effects of drugs on defibrillation capacity. Search terms included: antiarrhythmic drugs; cardiovascular drugs; amiodarone; sotalol; flecainide; propafenone; dofetilide; ibutilide; beta-blockers; lidocaine; procainamide; N-acetylprocainamide; mexiletine; disopyramide; moricizine; calcium channel blockers; defibrillation threshold; defibrillation energy requirements; defibrillation energy changes; defibrillation efficacy; implantable cardioverter defibrillators; and external defibrillators. Evidence from clinical studies indicates that amiodarone may increase defibrillation threshold (DFT). In addition, some data indicate that drugs including lidocaine, mexiletine, moracizine (moricizine), verapamil, venlafaxine and anaesthetic agents may increase DFT. In contrast, agents including sotalol, dofetilide and beta-adrenergic receptor antagonists (beta-blockers) may reduce DFT. Propafenone and procainamide appear to have minimal effect on DFT. For those antiarrhythmic drugs with both sodium and potassium channel blockade (e.g. amiodarone), the effect of sodium channel blockade predominates, resulting in an increase in DFT. Numerous drugs may affect defibrillation capacity. These effects must be considered when managing patients who have an ICD and require concomitant pharmacotherapy.