Electrical storm in patients with transvenous implantable cardioverter-defibrillators - Incidence, management and prognostic implications

Objectives. The purpose of this study was to determine the precise incidenc e, therapeutic options and prognostic implications of electrical storm in p atients with transvenous implantable cardioverter-defibrillator (ICD) syste ms. Background. Approximately 50% to 70% of patients treated with an ICD receiv e appropriate device based therapy within the first 2 years. Most arrhythmi c events require only one appropriate ICD firing for termination. However, some patients receive multiple appropriate shocks during a short period of time, a condition referred to as "arrhythmic or electrical storm." Methods. This prospectively designed observational study com prised 136 rec ipients of transvenous ICDs who were followed for 403 +/- 242 days. Electri cal storm was defined as ventricular tachycardia or fibrillation resulting in device intervention greater than or equal to 3 times during a single 24- h period. Results. During follow up, 57/136 patients (42%) received appropriate ICD t herapy. Electrical storm occurred in 14/136 patients (10%) at an average of 133 +/- 135 days after ICD implantation. The mean number of arrhythmic epi sodes constituting electrical storm was 17 +/- 17 (range: 3 to 50; median 8 ) per patient. In 12 patients, electrical storm required hospital admission . The arrhythmia cluster could be terminated by a combined therapy with bet a-blockers and intravenous amiodarone whereas class I antiarrhythmic drugs were only occasionally successful. The cumulative probability of survival a s estimated by the Kaplan-Meier method showed that patients with an episode of electrical storm did not have a worse outcome compared to those without such an event. Conclusions. Electrical storm represents a frequent event in patients treat ed with modern ICDs. It occurs most commonly late after ICD implantation an d can be managed by combined therapy with beta-blockers and amiodarone. Ele ctrical storm does not independently confer increased mortality. (J Am Coll Cardiol 1998;32:1909-15) (C) 1998 by the American College of Cardiology.