What is a Monophasic Defibrillator?

Monophasic Defibrillator. Big words. So, to the average person, what do they mean? They represent the standard defibrillator used in most hospitals, and the device gives a single pulse of electrical energy that goes in one direction between the two pads (or paddles) that are applied to a person’s chest. If a recording were made of this, it would show a single (monophasic) wave.

In a normal, healthy heart, its beat is regulated by electrical impulses that start in the sinus node. Sounds like it should be describing something in the nose; but, in fact, it is the natural pacemaker for the heart. From there, it fans out across the heart muscle along special tissue and causes the atria and ventricles to contract and expand in a regular pattern. The result? The heart fills and empties in a systematic fashion, thus insuring it fulfill its vital function for the continued life of the individual.

But, often there comes a time when the heart goes into what is known as Ventricular Fibrillation (VF), and then its organized electrical activity malfunctions, replaced by utter chaos. The result? The heart no longer fills and empties. Instead, it quivers (or fibrillates) and stops pumping altogether. If it is not corrected within several minutes, brain damage, nerve damage and/or death will result. That’s where a defibrillator comes in. It delivers an electrical jolt that, in essence, gives the chaos a "time-out" and allows the heart a chance to restart its regular electrical activity.

In order to work properly, a monophasic defibrillator often has to use high levels of electrical power. Often, a first jolt will be 200 joules. If a second shock is needed, the level rises to 300. If that fails, the device is increased to its highest level, 360 joules.

On the other hand, with a biphasic defibrillator the electricity goes from one pad, through the chest, to the second pad, and back. It reverses and therefore travels in two directions. As a result, it gives two jolts of electrical energy, and does so using less energy than a monophasic defibrillator. Rather than start with 200 joules, a biphasic device uses 100 to 150 joules, and 200 is normally the maximum amount.

Finally, the biphasic defibrillator has the ability to adjust itself based on the patient. It’s no secret that different people have different body types. As a result, the degree to which they resist the flow of electricity through their chest also differs. A biphasic defibrillator can determine this and modify the jolt it delivers, and improve the patient’s chance for survival. The monophasic defibrillators do not have this feature.

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