How to Determine if a Defibrillator is Monophasic or Biphasic
Check the device label, front panel, or manufacturer specifications—almost all modern defibrillators and AEDs sold today are biphasic, while monophasic devices are older units that are rarely manufactured anymore 1.
Practical Identification Methods
Primary Identification Approach
- Look at the device labeling: Most defibrillators clearly indicate the waveform type on the front panel or in the device specifications
- Check the maximum energy setting: Monophasic devices typically have maximum settings of 360 J, while many biphasic devices use lower maximum energies (120-200 J), though some biphasic units also go up to 360 J 1, 2
- Review the manufacturer documentation: The device manual or specifications will explicitly state the waveform type
Age and Manufacturing Context
According to AHA guidelines, biphasic waveforms are used in almost all AEDs and manual defibrillators sold today 1. Few monophasic waveform defibrillators are currently being manufactured, but many older units remain in use 1. If you're encountering an older device (pre-2000s era), it's more likely to be monophasic.
Technical Characteristics
Monophasic waveforms deliver current in one direction (one polarity) and include two subtypes 1:
- Monophasic damped sinusoidal (MDS) - returns to zero gradually
- Monophasic truncated exponential (MTE) - returns abruptly to zero
Biphasic waveforms deliver current that reverses direction during the shock 1, 2.
Clinical Relevance
While identification is important for documentation and energy selection, biphasic waveforms are more effective at terminating VF than monophasic waveforms 2. Biphasic shocks at lower energies (≤200 J) have equivalent or higher efficacy compared to monophasic shocks of equivalent or higher energy 1.
Common Pitfall
Don't assume all devices at the same energy setting deliver the same shock—actual pulse energy can deviate by up to +23% or -29% from the selected energy 3. The waveform type matters more for efficacy than the nominal energy setting alone.
If you cannot determine the waveform type from the device itself, contact your biomedical engineering department or the manufacturer directly for confirmation.