Transthoracic Incremental Monophasic Versus Biphasic Defibrillation by Emergency Responders - TIMBER


The goal of the trial was to evaluate biphasic defibrillation compared with conventional monophasic defibrillation for the termination of ventricular fibrillation (VF) in patients with out-of-hospital cardiac arrest treated by emergency medical technician (EMT) paramedics.

Study Design

Study Design:

Patients Screened: 862
Patients Enrolled: 168
Mean Follow Up: Hospital discharge
Mean Patient Age: Mean age 64 years
Female: 23

Patient Populations:

All adults in Seattle with nontraumatic out-of-hospital cardiac arrest occurring before EMS arrival who had an initial recorded rhythm of VF and received all defibrillator shocks by EMS personnel

Primary Endpoints:

Admission alive to the hospital

Secondary Endpoints:

Return of rhythm and circulation, survival to hospital discharge, and neurological status at discharge

Drug/Procedures Used:

Upon arrival at the cardiac arrest, EMTs started chest compressions with ventilation and administered shocks from automated external defibrillators (AEDs). Patients were assigned to defibrillation according to the waveform of the device deployed for the first shock. Randomization was performed at the level of each EMS unit, to which a monophasic or biphasic defibrillator was randomly allocated. The defibrillators were moved quarterly to ensure a balance in the use of biphasic and monophasic defibrillators by paramedics.

Principal Findings:

Monophasic shock was administered to 80 patients, biphasic shock to 68 patients, and mixed shocks to 20 patients. Bystander cardiopulmonary resuscitation was performed in 52% of patients. The cardiac arrest was witnessed in 71% of cases. Mean time from dispatch to first responder arrival was 3.5 minutes and from dispatch to first shock was 7.5 minutes.

There was no difference in the frequency of VF termination with first shock by treatment group (82% with monophasic vs. 88% with biphasic, p = 0.33). More shocks were needed for return of spontaneous circulation in the monophasic group, but the difference was not significant (mean 4.9 vs. 3.8, p = 0.18). There was no difference in the primary endpoint of admission alive to the hospital between groups (73% for monophasic vs. 76% for biphasic, p = 0.58). There was also no difference in survival to hospital discharge (34% vs. 41%, p = 0.35). Neurological outcome at hospital discharge did not differ by group (full recovery 54% vs. 52%, p = 0.4).


Among patients with out-of-hospital cardiac arrest treated by EMT paramedics, use of a biphasic defibrillator was not associated with a reduction in the primary endpoint of survival to hospital admission compared with use of a monophasic defibrillator.

Biphasic defibrillators offer the advantage of being smaller, having longer battery life, and allowing for conversion of patients with less energy. Despite these benefits, no clinical evidence of increased efficacy was observed in the present study. There was a trend toward the need for less shocks in order to return to spontaneous circulation in the biphasic group, but other endpoints were similar between the groups. Hospital admission rates were generally high in both groups. For example, in the ORBIT trial which also compared biphasic and monophasic defibrillation, only 57% of patients survived to hospital admission.


Kudenchuk PJ, Cobb LA, Copass MK, Olsufk M, Maynard C, Nichol G. Transthoracic incremental monophasic versus biphasic defibrillation by emergency responders (TIMBER): a randomized comparison of monophasic with biphasic waveform ascending energy defibrillation for the resuscitation of out-of-hospital cardiac arrest due to ventricular fibrillation. Circulation 2006;114:2010-8.

Clinical Topics: Arrhythmias and Clinical EP, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias

Keywords: Emergency Medical Technicians, Defibrillators, Out-of-Hospital Cardiac Arrest, Cardiopulmonary Resuscitation, Ventricular Fibrillation, Electric Countershock, Heart Arrest

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