Difference Between Monophasic and Biphasic Defibrillator

The key difference between monophasic and biphasic defibrillator is that the monophasic defibrillator is a type of defibrillation waveform where a shock is delivered to the heart from one vector as shown below.  Whereas, in biphasic defibrillation, shock is delivered to the heart via two vectors. In other words, monophasic shock is given in only one direction from one electrode to the other. In a biphasic shock, the initial direction of shock is reversed by changing the polarity of the electrodes in the latter part of the shock being delivered.

What is Defibrillation?

Defibrillation is a common treatment for life-threatening cardiac dysrhythmias and ventricular fibrillation. Defibrillation consists of delivering a therapeutic dose of electrical energy to the heart with a device called a defibrillator. Energy in a defibrillator is expressed in joules. A joule is the unit of work associated with one amp of current passed through one ohm of resistance for one second. When we express it in a formula, it is generally stated as follows:

Joules (Energy) = Voltage × Current × Time       

What is Monophasic Defibrillator?

In monophasic waveform, there is no ability to adjust for patient impedance or the resistance to the current exerted by the patient’s body, and it is generally recommended that all monophasic defibrillators deliver 360J of energy in adult patients to ensure maximum current is delivered in the face of an inability to detect patient impedance.

What is Biphasic Defibrillator?

Biphasic waveforms were initially developed for use in implantable defibrillators and now have become the standard in external defibrillators.

Implantable Defibrillator:

These are small implantable devices in the patient’s body which can detect abnormal heart rhythms and terminate them by delivering an instant current in the form of biphasic defibrillation.

External Defibrillator:

External defibrillators are large devices which can deliver biphasic defibrillation in a fatal cardiac rhythm abnormality when the patient is connected to the device. This is an essential equipment in the emergency room.

Biphasic waveforms have been shown to allow termination of ventricular fibrillation at lower current than monophasic defibrillators.

Automated External Defibrillator (AED), with Paddles

What is the difference between Monophasic and Biphasic Defibrillator?


Monophasic Defibrillator: Monophasic defibrillators are less popular in the current context.

Biphasic Defibrillator: Biphasic defibrillation is more common nowadays and used for implantable as well as external defibrillators.

Adjustment for Patient Impedance

Monophasic Defibrillator: Monophasic defibrillator is not able to adjust the current according to the resistance exerted by the patient’s body.

Biphasic Defibrillator: Biphasic defibrillators are capable of changing the current as per the patient’s impedance hence known to be more effective. Different manufacturers have used this functionality to produce different types of biphasic defibrillators.

Strength of the Current

Monophasic Defibrillator: Monophasic defibrillator uses a fixed current to deliver 360J energy to terminate cardiac arrhythmias.

Biphasic Defibrillator: In contrast, biphasic defibrillators can manually or automatically adjust the strength of the current, and it uses lesser strength than monophasic defibrillators.

Overall Effectively

Monophasic Defibrillator: Monophasic defibrillators are less efficient.

Biphasic Defibrillator: In contrast, biphasic defibrillators are more efficient.

Risk of Damaging Heart Muscles

Monophasic Defibrillator: Monophasic defibrillator has a greater risk of damaging the heart muscle as it delivers a greater current.

Biphasic Defibrillator: Biphasic defibrillator uses a smaller current and hence the damage is minimized.

Image Courtesy:

“Defibrillator (UOMZ)” by Yury Petrovich Masloboev – The photo was taken in educational-scientific center “Computer Diagnostic and Imaging” of Biomedical Systems Department of MIET. [CC BY-SA 3.0] via Wikimedia Commons