What are the Two Shockable Rhythms in Cardiac Arrest?

There are four main heart rhythms that can occur during a cardiac arrest. In this blog post, we will take a closer look at the two shockable rhythms.

A ‘shockable rhythm’ simply means the heart rhythm may be treated with defibrillation. If an Automated External Defibrillator (AED) detects a shockable rhythm is will recommend the rescuer delivers an electrical shock to the victim.

In Advanced Cardiac Life Support (ACLS), rescuers are trained to recognize a shockable rhythm on the defibrillator screen.

The two shockable rhythms in cardiac arrest are:

  • Ventricular Fibrillation (VF)
  • Ventricular Tachycardia (VT or V-Tac)

Ventricular Fibrillation (VF)

Ventricular Fibrillation occurs when the heart’s electrical conducting system becomes totally disorganized. Individual heart muscle fibres contract and relax in an uncoordinated and chaotic fashion. Therefore, the heart does not pump blood effectively and blood ceases to circulate.

Ventricular Fibrillation most commonly occurs after a heart attack. Without prompt defibrillation, the electrical activity will gradually cease and eventually stop.

The heart tracing below shows an example of VF.

Ventricular fibrillation (VF)

Ventricular Tachycardia (VT)

Ventricular Tachycardia (VT) occurs when the electrical activity originates from the bottom chamber of the heart (the ventricles). In VT, the ventricles may not have time to refill with blood.

Consequently, blood circulation may cease and the patient will rapidly go unconscious. In this situation, defibrillation may be effective in stopping all electrical activity and allowing a normal rhythm to recommence.

The heart tracing below shows an example of VT.

Ventricular Tachycardia (VT)

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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