Acute Mechanical Response to Anti-arrhythmic Drug Therapy

Amiodarone therapy is used frequently for control of ventricular arrhythmias in patients who receive painful shocks from an implantable cardioverter-defibrillator (ICD). Data in post-myocardial infarction (MI) patients and ICD patients suggest that amiodarone is mortality-neutral; it neither confers increased nor decreased mortality. However, these data are derived from patients largely with normal intraventricular conduction, manifesting as a QRS complex duration on the surface ECG <120 ms. Amiodarone, in addition to potassium-channel blocking effects, is a sodium channel-blocker. Because sodium channels mediate cardiac depolarization, and a QRS complex >120 ms is indicative of abnormal depolarization, amiodarone may not be benign in patients with such conduction defects. Patients with cardiac resynchronization therapy-defibrillators (CRT-D), who all have abnormal baseline intraventricular conduction, may therefore be adversely affected by amiodarone. Anecdotal clinical data suggest that this may be the case, but the question of amiodarone's cardiac safety profile in CRT patients has never been studied.