What is the difference between monophasic and biphasic defibrillators?


What is defibrillation?

Defibrillation is a procedure used to treat life-threatening conditions that affect the heart’s rhythm, such as arrhythmias, ventricular fibrillation and pulseless ventricular tachycardia.

The process involves delivering an electric shock to the heart, causing the heart muscle to depolarize and re-establish normal conduction of the heart’s electrical impulses. The machine used to deliver this therapeutic shock to the heart is called a defibrillator.

What is monophasic defibrillator?

A Monophasic Automated External defibrillators (AED) are devices that deliver an electric shock. It sends a current in a single direction from one electrode on one side of the chest to the other. Monophasic waveform defibrillation has been used since the invention of AED devices. It was replaced by more effective defibrillators due to technological and scientific advances.

In Monophasic defibrillation, the voltage height of the capacitor during charging determines the energy subsequently provided by the electrode sheet. The waveform associated with Monophasic defibrillation has a peak, which is critical in determining the success of defibrillation. Enough electricity is needed to reach the heart to stop the fatal rhythm or tremor. At the same time, excessive peak currents must be avoided, which can damage the patient’s heart. In Monophasic machines, the current delivered is high, which is why these machines are usually larger.

What is a Biphasic defibrillator?

Biphasic defibrillators are devices that use bidirectional electric currents to flow, as opposed to Monophasic Automated External defibrillators (AED), where electricity flows in one direction. Introduced in 1996, the direction of the current reverses at some point in the defibrillation cycle during the discharge of the device as the shock from the devices hits.

What is the difference between monophasic and biphasic defibrillators?

Model monophasic defibrillator biphasic defibrillator
Availability Not very popular in the current light. More common now, used in implantable and external defibrillators.
Adjusting patient impedance Unable to adjust electric currents to the drag imposed by the patient’s body. Able to change electrical currents based on a patient’s impedance, and thus known to be more effective. Different manufacturers have used this feature to produce different types of Biphasic defibrillators.
The intensity of electric current  Used a fixed electric current to deliver 360J of energy to stop arrhythmias. By contrast, electric current strengths can be tuned manually or automatically, and are smaller than those used by single-phase defibrillators.
The overall effective This defibrillator is less efficient. By comparison, the defibrillators were more effective.
Risk of damage to the heart muscle Provide bigger electric shocks, and therefore greater risk of damaging heart muscle. Uses smaller electrical currents, thus causing minimal damage.


Technological advances have made Automated external defibrillators (AED) fully Automated, providing clear verbal instructions to operators that can determine if a patient is in an absorbable rhythm (ventricular fibrillation/ventricular tachycardia), And the operator is not allowed to provide an electric shock if the patient’s heart is not in a rhythm that can shock. Therefore, laymen with little or no formal cardiovascular training are unlikely to harm patients by providing defibrillation. Automated external defibrillators (AED) today simply “charge up” and allow rescuers to deliver “shocks” if the patient is in an identifiable lethal rhythm.

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In addition, by allowing lower current transfer, the monophasic technique significantly reduces the most common risks associated with defibrillation of electrical skin burns at the electrode site. Other common risks, including the risk of stroke from flowing blood clots, also decreased significantly in proportion to the level of trauma to the body. This should not in any way detract from the significant positive impact on survival in countless cases due to the advent of monophasic external defibrillators, to which the lives of countless victims of ventricular fibrillation are attributed.