Monophasic vs. Biphasic AED Shocks — Learn the Difference

The terms Monophasic and Biphasic refer to two different shock techniques that can help save a person’s life during Sudden Cardiac Arrest (SCA). You may have heard these words in the context of Monophasic Defibrillators vs. Biphasic Defibrillators, and in this article, we’re breaking down the differences below.

Defibrillation with an AED, or Automated External Defibrillator, is a crucial step to restoring the heart to normal rhythm and reviving someone who has suffered SCA. Anyone can use an AED, including children, and AEDs safely analyze a patient’s heart rhythm before determining if an electrical shock can help.

An important part of defibrillation is the waveform of the electric shock that it delivers to the heart. There are two main types: monophasic and biphasic.  

Before diving into preferences, it should be acknowledged upfront that both types of waveforms have roughly the same efficacy in saving someone’s life; however, there are many perks of using a biphasic defibrillator, which is why biphasic has become the more common, preferred type of device.

What are Waveforms? 

Electricity is made up of charged atoms. These charged atoms move through space in the shape of a wave, forming what is called a current. Waveforms are the direction a current takes. 

Reminder: Luckily, you do not need to be an expert on waveforms (or even know what they are) to successfully operate an AED and save someone’s life from SCA. AEDs are safe, easy to use, and designed to be successfully used by ANYONE, including children. 

What is Monophasic Defibrillation?

Monophasic defibrillation sends an electric current in one direction. In the context of a monophasic AED, the current travels straight to the heart.  

What is Biphasic Defibrillation?

In contrast to the single current of monophasic defibrillation, biphasic defibrillation sends a  current in two directions, consisting of two stages. In the first phase, electricity goes out from one electrode toward the other, just as it does in monophasic defibrillation. In the second phase, the electrical current returns back to the originating electrode. In the context of AED shocks, this means biphasic shocks travel to the heart and back through it a second time as they return to their source, the AED pads.  

All AEDs on the market today use biphasic defibrillation techniques, including the Avive Connect AED™.

While neither waveform has proven to be superior in improving the rate of ROSC or survival from SCA, biphasic waveform defibrillators expose patients to a much lower peak electric current (with equal or greater efficacy than monophasic defibrillators do), which makes them the safer, preferred type of defibrillators.

Today, biphasic defibrillation has largely replaced monophasic as the superior method, so much so that monophasic devices are no longer manufactured. The newest AED to hit the market, the Avive Connect AED™, uses biphasic waveform. While both waveforms have been proven effective in restoring a normal heart rhythm, they differ in several important ways. 

Monophasic vs. Biphasic: Read the Differences 

Popularity, Effectiveness & Safety

Research shows similar survival outcomes for patients who have received AED shocks from a monophasic defibrillator and those who have had shocks from an AED with biphasic defibrillation. However, despite the dual current, biphasic defibrillation actually requires less energy to administer a lifesaving shock compared to its monophasic counterpart. Since biphasic defibrillators require significantly lower levels of energy, they can cause less damage to the surrounding organs and tissue, making them the safer, preferred method. 

Because biphasic defibrillators use less energy, they are also generally smaller and lighter than monophasic ones. As a result, biphasic AEDs are more portable, making them more often used in public spaces.

In plain terms, Avive’s electrical engineer, Andrea Martin, explains, “Using a biphasic shock for the Avive Connect AED allowed us to create a high efficacy product that is also very small and energy efficient. The biphasic waveform gives you the same, or better result, for a lot less energy, so there’s less risk there.”

Strength of the Current

The strength of the current is another important, differentiating factor between monophasic and biphasic defibrillators. Research has shown that biphasic defibrillation achieves similar success rates in helping SCA patients survive while delivering less energy. Monophasic defibrillation delivers a high-energy electric pulse, anywhere from 200-360 joules per shock, whereas biphasic defibrillation delivers an initial shock in the 120-200 joules range. 

Battery Life

Biphasic defibrillators typically have a longer battery life than monophasic defibrillators. Because biphasic defibrillators use a lower-energy electric pulse, it takes less power for them to deliver a shock, which allows the battery to last longer. Meanwhile, monophasic defibrillators use a higher-energy electrical pulse that requires more power to deliver, which can drain the AED battery more quickly. 

If you’re considering purchasing an AED and battery life is important to you, the Avive Connect AED has the only FDA-approved embedded rechargeable AED battery that will last throughout the life of the device.

The Preferred Method?

When it comes to purchasing a public access defibrillator, biphasic AEDs are commonly accepted as the better option for many reasons. Biphasic AEDs are smaller, lighter, and have a longer battery life than monophasic AEDs. They are often more widely available than monophasic defibrillators, and can be less intimidating for the user to approach. 

Ultimately, though, when it comes to cardiac arrest, the “best” AED is the closest AED, and it would be far better to use a monophasic AED when responding to a cardiac arrest emergency than no AED at all. Although, if you are purchasing an AED for the first time, we recommend a biphasic defibrillator.

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