Biphasic Defibrillation: Is there a better biphasic?

This article is posted by Nikhil Kanamala based on the presentation by Sofian Zeina in the Biomedical Engineering meeting on October 2017 to educate staff on new and emerging technologies.  The information presented in this blog is based on the ECRI recommendations.

Biphasic waveforms are generally considered the gold standard for defibrillators and are preferred over their monophasic counterpart mainly because monophasic waveforms due to their higher energy and current levels are more likely to cause burns.  Other contributing factors such as decrease in availability and confusion caused in hospitals between choosing monophasic or biphasic has seen a decline in the demand for purchasing and using monophasic waveform defibrillators.

The monophasic and biphasic waveforms are represented below in Figure 1:

Figure 1:  Monophasic vs Biphasic waveform.  Current flows in one direction in monophasic, whereas in two phases in biphasic.

Amongst the biphasic defibrillators, there are different types based on the waveform shapes which are:

·       Biphasic Truncated Waveform (BTE) – For low impedance internal cardiac applications.  Adapted for external defibrillation by Philips and Medtronic.

·       Rectilinear Biphasic (RLB) – Developed for external defibrillation.  Takes into account high and varied patient impedance levels.  Only zoll uses this waveform.

·       Pulsed Biphasic Waveform – Not cleared for use in USA or Canada.

BTE and RLB waveforms are shown in figures 2 and 3 respectively.

 Figure 2: BTE waveform.

Figure 3: RLB waveform.

Biphasic waveforms have been proven to be safe and effective for defibrillation and cardioversion.  However, it has been difficult to statistically differentiate the biphasic waveforms used (BTE vs RLB) and prove the success of one waveform over the other.  Biphasic defibrillators compensate for patient impedance in different ways, such that a shock from one Philips defibrillator for example will not have the same peak current, average current, and pulse duration as a shock from Zoll defibrillator, even on the same patient.  It would be hard to choose one over the other in such cases.

There are a few recommendations made regarding biphasic waveforms:

·       First shock energy of at least 120J for RLB and 150J for BTE waveforms.

·       Defibrillators should meet the facility’s needs for device application

·       Ease of use

·       Standardization on one supplier’s unit or a supplier’s product line.

·       Consider a plan to phase out all monophasic defibrillators

·       Do not use the waveform or energy protocol as a deciding factor in selecting among biphasic defibrillators

·       The healthcare facility should follow the supplier’s recommendations for the appropriate energy levels for each shock.

When phasing out defibrillators, the following should be considered:

·       Each defibrillator is clearly labeled with the recommended energy levels for that waveform type

·       Users know the energy protocol to be used with each waveform type

·       Finally, consider redistributing defibrillators so that staff members are using only one type of waveform.