Why Early Defibrillation is Important

A defibrillator is a life-saving machine that gives the heart an electrical shock during a cardiac arrest. This is called defibrillation.

Many people think that defibrillation starts the heart after it has stopped. This is not the case – defibrillation stops a heart which is beating ineffectively and allows it to restart in a natural rhythm (sinus rhythm).

Cardiac arrest occurs when the heart stops pumping blood around the body. When someone has a cardiac arrest, the earlier they are defibrillated the better the chance of survival.

Once the heart stops beating effectively the flow of oxygenated blood around the body reduces and eventually stops. Vital organs will start to die when they loose their supply of oxygen rich blood. The brain for example will start to die within minutes.

Early CPR and early defibrillation is extremely important following a cardiac arrest. The earlier effective CPR and defibrillation is received the higher the chance of survival.

The graph below gives an indication of the increase in survival rate of patients following cardiac arrest if CPR and defibrillation are received quickly, resulting in an increase in survival rate of up to 60 – 70%.

Shockable Rhythms

A defibrillator will only deliver an electrical shock if the patient is in a ‘shockable rhythm’ during the cardiac arrest.

Shockable rhythms are rhythms caused when the normal electrical activity of the heart that causes the regular heartbeat become disturbed. The disordered electrical activity causes the heart to quiver in an uncoordinated fashion which prevents it from effectively pumping blood around the body.

There are 2 rhythms that are shockable.

  • Ventricular Fibrillation (V-Fib)
  • Pulseless Ventricular Tachycardia

In both cases, the disordered electrical activity has to be stopped, which is achieved by passing a large electrical charge across the heart using a defibrillator. This process is known as defibrillation.

Non-Shockable Rhythms

Asystole is a non-shockable rhythm because no electrical activity is taking place in the heart. There is no attempt being made by the heart to beat. Shocking a patient who is in Asystole would have no effect as there is no electrical activity to stop.

In addition to asystole, Pulseless Electrical Activity (PEA) is also a non-shockable rhythm. In this case the electrical activity in the heart is still taking place but the heart is physically not beating

In both these situations, an Automated External Defibrillator (AED) will not deliver a shock. The only treatment is effective CPR until the arrival of eemergency medical help.

John Furst

JOHN FURST is an experienced emergency medical technician and qualified first aid & CPR instructor. John is passionate about first aid and believes everyone should have the skills and confidence to take action in an emergency situation.

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