How do defibrillators work?

Remember those frightening scenes in a movie where an Emergency Responder (ER) would yell - "Clear!" before jolting electricity through a patient using a device with large paddles? That device is called a defibrillator.

But now those machines have evolved, into a lightweight, portable medical device, called Automated External Defibrillators (AEDs). This new portable device is available to the public, simple to use, and saves lives.

Many people know very little about what an AED machine is, let alone knowing how or when to use one. But it’s always a good idea to learn about these life saving devices. Yours may just save a life one day.

​The more you know about AEDs and how they operate, the more likely you are to confidently intervene and save someone in Sudden Cardiac Arrest (SCA). This is important!


What Happens During Cardiac Arrest?
Sudden Cardiac Arrest (SCA) occurs when the heart stops beating abruptly due to ventricular fibrillation (VF), a problem within the heart's electrical system.
When this happens, the circulatory system to the brain and the rest of the body stops, and the sufferer collapses in an unconscious state. The halt in the blood flow damages tissues soon after, leading  to death if left unattended.

SCA is caused by disturbances in heart rhythm. The heart's muscles function in sync owing to the consistent rhythm of certain electrical activity inside the heart. Disturbance or inconsistency in this behaviour leads to irregular heartbeats - it either becomes too fast or too slow. This irregularity in the heartbeat is called arrhythmia.

When left unattended, arrhythmia leads to ventricular fibrillation (VF) which occurs when the heart muscles quiver or flutter instead of contracting in a coordinated way. This is when SCA can begin to occur. It may also show as a normal-looking electrical rhythm without a pulse (pulseless electrical activity or electromechanical dissociation). A severe case would be when the heart and the electrical rhythm ceases completely, which is known as asystole or cardiac flatline.

Most cases of sudden cardiac arrest happen due to coronary artery disease or other structural cardiac problems. Some of these conditions may be inherited. But they alter the electrical activity of heart muscles, increasing the risk of arrhythmia.

Injuries, significant bleeding, poisoning, electrocution, or drowning may cause SCA. Sudden cardiac arrest often has no warning signs or symptoms. It may cause chest pains, shortness of breath, dizziness, nausea and blackouts.

A lack of steady pulse causes loss of breathing and consciousness. Heart attacks (myocardial infarction) are caused by reduced or stopped blood flow to a portion of the heart. Heart attacks can also increase the risk of cardiac arrest. .


What is a Defibrillator?
A defibrillator is a medical device that treats ventricular fibrillation. To do so, the defibrillator sends a short electrical current through the heart, depolarizing cardiac muscle and resetting the body's natural pacemaker.

A pair of electrodes, placed over an electricity-conductive gel, facilitates this current by sending the difference in voltage. The gel lowers the natural resistivity of human tissues and avoids electrical burns. In addition to metal paddles with insulated grips, some contemporary defibrillators utilise adhesive pads with conductive gel already attached.

Different kinds of Defibrillators are available today, depending on their mode of application. Manual defibrillators, the ones most popular among common people, need expert training in order to operate correctly. Before administering the electrodes, the operator manually adjusts the voltage and duration of the voltage using an electrocardiogram which may be built-in or separate.

The conductive gel can also be applied manually before usage.  Paddle electrodes are almost exclusively seen in hospitals, on manual external defibrillators often with disposable conductive gel pads. With practice, the paddles can be placed and activated quickly, saving time and preventing tissue damage.

When placed on the sufferer’s chest, automated external defibrillators have preset voltages and can detect cardiac rhythms. The AED will not administer the shock until treatable ventricular fibrillation is detected, thus the user need not be trained. Hence, AEDs are best used for cardiac arrests outside of the hospital.

AEDs are also available for high-risk patients. Manual internal defibrillators are sometimes utilised in open-heart surgery or in the emergency room

Like artificial pacemakers, implantable cardioverter-defibrillators are surgically implanted and are designed to monitor cardiac rhythms and intervene when required to treat arrhythmia. Patients who don't require an ICD right away may utilise wearable models.


At Emcare we provide high-quality live workshops on how to operate an AED, and train individuals to be ready for any unexpected circumstance.
Sign up to our workshops happening throughout the year, it could save a life.