Aug. 11, 2025
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.
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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.
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.
Monophasic defibrillation sends an electric current in one direction. In the context of a monophasic AED, the current travels straight to the heart.
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.
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.”
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.
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.
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.
The Avive Connect AED delivers biphasic shocks to patients suffering from SCA.
Cardioversion is the name for returning a heart from an irregular heart rate to a normal one. For decades, researchers recommended biphasic shocks during cardioversion. However, monophasic shocks can also help with cardioversion. And recent recommendations from the American Heart Association (AHA) say that it is hard to compare how effective the two different waveforms are at cardioversion because the defibrillators available today use different electric patterns to send out shocks.
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The joules of monophasic shocks are higher than those of biphasic. A monophasic shock typically has a sequence of 200- 360J, and a biphasic shock is much lower, between 120-200J.
Biphasic and monophasic AEDs deliver different amounts of energy, even when set to the same level. As a result, recommended energy levels vary from device to device. So, the AHA says to always follow the manufacturer's instructions for what energy levels to use for that defibrillator's specific pattern.
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Monophasic AEDs are devices that emit a type of shock. It sends an electrical current in a single direction from an electrode on one side of the chest to an electrode on the other side. Monophasic waveform defibrillation has been used since the invention of AED devices. And thanks to the advancements in technology and science, it is replaced by more effective defibrillators.
In monophasic defibrillation, the height of the voltage of the capacitor during charging determines the energy that is then delivered by the pads. The waveform linked with monophasic defibrillation has one peak, which is crucial in determining the success of defibrillation. There needs to be enough current to reach the heart in order to terminate the lethal rhythm or fibrillation. At the same time, it is necessary to avoid excessively high peak current, which could damage a patient's heart. In monophasic machines, the delivered current is high, which is why these machines were usually on the bulkier side.
However, most manufacturers have ceased production of monophasic AED devices and have started producing biphasic AED. In turn, most hospitals are using a combination of newer defibrillators and older devices [1].
Biphasic waveform defibrillators are devices that utilize bidirectional current flow as opposed to monophasic AED, where the current flows are in one direction. These defibrillators were introduced in , and with the shocks emitted by these devices, the direction of current flow is reversed at some point in the defibrillation cycle during the discharge from the device.
In biphasic AEDs, the pulse is composed of a positive and negative peak. During the positive peak, the current moves from electrode A to electrode B and vice versa during negative peak, i.e., from B to A. Modern AEDs first measure the impedance of the thorax (the body’s resistance to the current) and adjust the voltage level accordingly. What’s more, devices such as BeneHeart C Series of Mindray come with adult and child modes. This allows rescuers to immediately select the correct mode, which then enables the device to do its job with even greater efficacy.
The exact shape of the current delivery is determined by factors such as the current, energy of direction, and duration of delivered energy. What makes biphasic devices so important is that they adjust for patient impedance through varied characteristics of the waveforms to make sure that high- and low-impedance patients have the same chances of survival. It is particularly important if we bear in mind that the most effective waveforms maintain their shape and duration regardless of the impedance [2], and that’s exactly what biphasic devices can achieve.
Besides the main difference in the current flow, biphasic AED also differ from monophasic devices because they achieve the same effect but with a lower number of joules. In fact, there is evidence to prove that the efficacy that a protocol using monophasic waveform shocks in the 200-360J sequence is 90% similar to that of a protocol utilizing biphasic waveform shocks in 120-200J sequence. Therefore, what we can see here is that the higher efficacy can be achieved with biphasic AEDs as opposed to the monophasic ones when they are with the equal level of delivered average energy. In order to achieve better resuscitation outcomes for patients who are typically difficult to defibrillate, such as those with obesity or higher impedance, Mindray has developed the 360J biphasic technology and integrated it into the AED devices to increase the termination rates of refibrillation.
What’s more, biphasic waveform defibrillation produced less impairment of cardiac function as measured by arterial pressure, recurrence of heart rate, and echocardiography [3].
The very first defibrillators were monophasic devices, and they have been used for a long time until the invention of biphasic defibrillators. Even though the use of monophasic defibrillators continued, the biphasic devices have become more common so that many companies don’t produce the older machines anymore. But it is impossible not to wonder about the quality of these defibrillators when compared side by side. Are biphasic AED defibrillators really better? They are not just trendy in the healthcare industry, lightweight, and easy to spot, but biphasic machines really are better than their older counterparts.
Reasons for the supreme position of biphasic machines are numerous, including the above-mentioned fact that the biphasic AEDs can achieve higher efficacy but with the equal or even lower amount of delivered energy. At the same time, they also produce less impairment of cardiac function, which is always important.
Another benefit of biphasic defibrillators is that they normally do not produce other negative effects such as skin burns, which can happen with their monophasic counterparts. Moreover, since they require a lower amount of energy to produce the same effects, biphasic AED machines are usually lighter, smaller, less demanding on batteries, and require lower maintenance than monophasic defibrillators.
On the flip side, monophasic devices can be quite bulky and impractical to handle in hectic situations. As the technology keeps progressing alongside science, biphasic machines are becoming more versatile and practical in terms of features and options they provide to rescuers.
Although monophasic and biphasic machines are successful in performing defibrillation, the latter is considered a better option. They are more convenient, accurate, effective, and cost less and are able to prevent further damage to the heart. Biphasic machines require relatively lower peak current in order to lower the risk to heart damage, and are able to adjust impedance to work equally on different types of patients. Biphasic devices are going to completely take over the world as many companies stopped producing their older counterparts.
[1] Richard J. Green. Confusion between monophasic and biphasic defibrillators. Resuscitation journal. March Volume 68, Issue 3, Pages 433–434. Available at: https://www.resuscitationjournal.com/article/S-(05)-0/fulltext (Accessed: 27 February )
[2] Biphasic Defibrillation: The Shape of Resuscitation Today. (). Available at: https://www.emsworld.com/index.php/article//biphasic-defibrillation-shape-resuscitation-today (Accessed: 27 February )
[3] M Scholten, T Szili-Torok, P Klootwijk, and L Jordaens. Comparison of monophasic and biphasic shocks for transthoracic cardioversion of atrial fibrillation. Heart. Sep; 89(9): –. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC/(Accessed: 27 February )
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