Out-of-hospital cardiac arrest rectilinear biphasic to monophasic damped sine defibrillation waveforms with advanced life support intervention trial (ORBIT)☆
Introduction
Currently available external defibrillators for routine use by emergency medical services (EMS) personnel deliver monophasic (damped sinusoidal) or biphasic (current flow reversal during the shock) waveform shocks. The issue about which waveform is more effective in out-of-hospital cardiac arrest remains undecided. Biphasic waveforms defibrillate with lower energy, and initial shocks are more often successful in the electrophysiology laboratory, with implanted defibrillators [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16] and when used by first responders in the setting of out-of-hospital cardiac arrest (OHCA) [7], [8], [9], [10]. However, none of the prior randomized trials in out-of-hospital ventricular fibrillation (VF) were able to show improved survival to hospital admission or discharge despite greater efficacy in terminating VF [8], [9]. This may in part be attributed to the fact that both out-of-hospital trials were randomized at the level of the first responder using automated external defibrillators. Neither out-of-hospital trial studied the relative efficacy of using ascending biphasic energy levels nor did they conduct lower energy level comparisons between biphasic and monophasic waveforms. In addition, not all biphasic waveforms are identical. Current ALS guidelines recommend either waveform, specifically ascending monophasic energy levels and either fixed or ascending biphasic energy levels [11].
The purpose of this study was to compare patient outcomes after VF treated with ascending energy shocks using a rectilinear biphasic waveform or a monophasic damped sine waveform in an advanced life support setting for the resuscitation of OHCA patients treated by Emergency Medical Technician-Paramedics (EMT-P).
Section snippets
Study design
The out-of-hospital rectilinear biphasic trial (ORBIT), was a prospective, randomized, controlled trial of OHCA patients, comparing a control group receiving monophasic damped sine (MDS) defibrillation with a treatment group receiving rectilinear biphasic (RLB) defibrillation. The study used block randomization where a single ambulance station represented one block (“proc plan” SAS v 8.02). A central randomization unit used computer-generated random number tables to prepare a separate block
Study enrollment
There were 538 patients enrolled (Fig. 1). Ninety-six cases were removed prior to validation because of incomplete documentation (53), non-randomized device (41), and family request (2). The central validation committee removed 13 cases of which 5 were not in VT or VF, one was traumatic in origin and 7 cases which were grouped as other (Fig. 1) leaving 429 validated cases. Thirty-eight EMS witnessed cases were removed prior to describing the study population demographics (see Section 2). There
Discussion
The main result of this study indicates that for out-of-hospital VF initially treated by ALS paramedics, RLB shocks are more effective at converting VF and pulseless VT to an organized rhythm than MDS shocks within the first three shocks when administered in sequence with escalating energy levels beginning at 120 J for RLB and 200 J for MDS However, despite an increased rate of return to an organized rhythm, neither the rate of return of spontaneous circulation nor the survival rates were
Limitations
Randomization compliance was 94% at the level of the station and was 80% at the level of the patient. The unpredictable nature of the EMS environment, the size and complexity of the EMS system and the critical nature of the call necessitating creative immediate solutions to device failures or shortages contributed to a reduction in randomization compliance at the level of the patient This theory of random error was supported by an intention-to-treat analysis which was similar in magnitude and
Conclusions
Shock success to an organized rhythm comparing step-up protocol for energy settings demonstrated that the rectilinear biphasic waveform was superior to the monophasic damped sine waveform in advanced life support treatment of out-of-hospital cardiac arrest. Survival rates showed differences between waveforms in the early circulatory phase and demonstrated decline as the time to first shock increased.
Acknowledgements
The Advanced Life Support paramedics of Toronto, Ontario, Canada represented by the Toronto Paramedic Association and Canadian Union of Public Employees local 416, and the Sunnybrook and Women's Land Base Hospital Program provided support in the implementation of the trial. Dr. Richard Kerber contributed significantly to the editing of this manuscript. Dr. Alexander Kiss contributed significantly to the survival curve analysis. This study was supported by a grant from ZOLL Medical Corporation,
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A Spanish translated version of the Abstract and Keywords of this article appears as Appendix at 10.1016/j.resuscitation.2004.11.031.