Antiarrhythmic drugs and ventricular defibrillation energy requirements

To understand the potential interaction between antiarrhythmic therapy and the implantable cardioverter-defibrillator (ICD) in patients who receive pharmacologic therapy as an adjunct to ICD therapy.

MEDLINE searching was employed and the information was indexed from approximately 3600 journals published world-wide from 1966 to 1998.

Data were collected from 66 of approximately 455 originally identified articles and abstracts using explicit methodological criteria.

The ICD therapy has been widely used for therapy of life-threatening ventricular arrhythmias (VT/VF) and prevention of recurrence of sudden cardiac death. Studies reported that 40%-70% or 10%-40% of ICD patients required concomitant antiarrhythmic medication to reduce the frequency of sustained arrhythmic episodes and to minimize the frequency of device discharges. Most studies on antiarrhythmic drug-ICD interactions have been performed in experimental animals. Antiarrhythmic drugs can influence the effectiveness of ICD to terminate arrhythmias through their effects on defibrillation threshold (DFT). Studies have demonstrated a rise in DFTs with class Ib agent lidocaine and class Ic agents encainide and flecainide. Class Ia agents, as well as amiodarone, bretylium and propafenone may have more variable effects on DFT probably because of the difference between acute and chronic drug dosing, dose-related changes, active metabolites, and reproducibility in determining DFT. Class III agents, with the exception of amiodarone, consistently decrease DFT. These drugs can be used as front-line agents in ICD patients.

Antiarrhythmic drugs can increase, decrease, or have no effect on DFT. Class III agents except amiodarone can be safely administered in conjunction with ICD patients as long as the interaction between these therapeutic modalities is appreciated.