Amiodarone for Shock-Refractory Ventricular Fibrillation
Source: Kudenchuk PJ, et al. N Engl J Med 1999;341(12):871-878.
Kudenchuk and associates at the university of Washington and the Seattle Fire Department performed this study to determine whether the administration of amiodarone to patients with cardiac arrest due to ventricular fibrillation (VF) or pulseless ventricular tachycardia (PVT) who had not responded to initial measures improved initial survival. Study patients comprised 504 persons out of a total of 3954 consecutive patients treated in the field for cardiac arrest during the 29-month study period. Patients with nontraumatic cardiac arrest were eligible for the study if they had been endotracheally intubated and remained in VF or PVT after receiving three or more precordial shocks and other therapy according to the American Heart Association’s Guidelines for Advanced Cardiac Life Support. In a randomized, double-blind fashion, after administration of 1mg epinephrine intravenously, paramedics on the scene gave the patients either 300 mg amiodarone or placebo intravenously.
The patient groups receiving amiodarone and placebo, respectively, were well matched for age (mean 66 vs 65), gender (76% vs 79% male), cardiac and other medical history, whether bystander CPR was administered, initial cardiac arrest rhythm, and mean time from dispatch to response or procedure (4.3 vs 4.4 min).
Of the 246 patients who received amiodarone, 44% survived to hospital admission, as compared to 34% of the 258 patients who received placebo (P = 0.03), a 29% improvement.
After adjustment for other independent predictors of outcome (e.g., location of arrest, paramedic response time, initial rhythm, presence or absence of bradycardia or hypotension prior to study drug administration, and previous therapy), the odds ratio for survival to admission to the hospital was 1.6 (95% CI, 1.1-2.4; P = 0.02) in favor of amiodarone. Of the 504 study patients, 67 survived to hospital discharge, 13.4% of the patients receiving amiodarone vs. 13.2% of those who got placebo. The trial did not have sufficient statistical power to detect significant differences in patient survival to hospital discharge.
Comment by David J. Pierson, MD, FACP, FCCP
This study was conducted in the field, using Seattle’s superb multitiered prehospital emergency response system. It could not have been carried out in most cities in the world—even in most large North American cities—and it may be a while before a similar study is performed on patients who suffer ventricular fibrillation in the hospital. Thus, although its clinical setting and patient population differed from those encountered in the ICU, this study’s data are unlikely to be augmented by findings more directly applicable to critical care practice.
As a result of this study’s findings, amiodarone seems certain to see wider use during shock-refractory cardiac arrest in other clinical settings, including the ICU. Especially in the latter setting, better patient characterization, response times, and dose adjustment should be possible, and thus outcomes could be better than observed in the field. On the other hand, outside the settings of the operating room and the coronary ICU, critically ill patients who suffer cardiac arrest in an ICU tend to have underlying medical conditions, rendering the prognosis unfavorable. Still, the availability of amiodarone may make it possible to successfully resuscitate some patients in whom efforts would otherwise be unsuccessful, at least initially, if the results of this study prove valid.