Evaluation of defibrillation safety margin in modern implantable cardioverter defibrillators after administration of amiodarone

The adjunctive medication with amiodarone plays a major role in patients with an implantable cardioverter defibrillator (ICD). Amiodarone as class III antiarrhythmic drug may significantly alter the defibrillation threshold (DFT). Conflicting results exist on the clinical relevance of a DFT rise on amiodarone. The only prospective study on this issue included only a small number of patients on amiodarone. The purpose of this study was to assess the safety and clinical relevance of repeat defibrillator testing after initiation of amiodarone in modern defibrillator systems.

We assessed risks and clinical consequences of retesting defibrillation safety margin after initiation of amiodarone in 130 consecutive patients. All patients underwent intraoperative testing at the time of first ICD implantation. A repeated VF induction and defibrillator test (by protocol with a single shock and 10 J safety margin) after a total dose of at least 10 g amiodarone 4–6 weeks after initiation of medication was performed. DFT testing after initiation of amiodarone was safe as there were no complications that led to a prolonged hospital stay. In 4 of 114 patients with a left-sided device (1.6%) and 3 of 7 patients with a right-sided device (42.8%), a 10 J safety margin could not be achieved. As a result 4 patients (3.1% of study collective) had a revision of the system.

Repeat defibrillation testing after administration of amiodarone therapy rarely fails in patients with left-sided devices. We observed a higher test failure in patients with a device in the right-subpectoral position although this subgroup was small. Repeat defibrillator testing is safe as no relevant complications were observed.