Which heart rhythms can a defibrillator shock?

When someone suffers cardiac arrest the only definitive treatment is CPR and a shock from a defibrillator, but a defibrillator will only shock what it deems as a “shockable rhythm”.

An Automated External Defibrillator (AED) will first analyse the rhythm of the casualty’s heart and only deliver a shock if the heart is in a certain rhythm, but what is a shockable rhythm?

What does a defibrillator do?

A defibrillator is designed to deliver an electrical shock to a patient whose heart is in cardiac arrest and not effectively pumping blood around the body.

A defibrillator shock stops the heart momentarily, allowing the body’s natural pacemaker to kick the heart back into a normal rhythm.

Ventricular Fibrillation

Ventricular Fibrillation (VF) refers to an arrhythmia of the heart in which the lower chambers contract rapidly and in an uncoordinated way.In simple terms, the heart can be described as “quivering”.

Blood is not being pumped around the body during Ventricular Fibrillation.

Someone experiencing Ventricular Fibrillation will fall unconscious and require resuscitation to prevent brain damage and death. Immediate CPR and use of a defibrillator is needed for the best chance of survival.

Pulseless Ventricular Tachycardia

Pulseless Ventricular Tachycardia differs from VF in that the heart, rather than quivering, beats extremely quickly. The speed of the heart’s contractions doesn’t allow its chambers to fill with blood and therefore it can’t pump blood effectively.

Similar to Ventricular Fibrillation, the individual will fall unconscious quickly and stop breathing. Begin CPR immediately and locate an AED.

Asystole

The most serious form of cardiac arrest which is usually irreversible; Asystole usually follows one of the previous arrhythmias and is a complete lack of activity in the heart. It is also referred to as a “flatline”.

Survival rates for an Asystole rhythm are considerably lower than other arrhythmias. CPR can keep the heart pumping but the Asystole is not classed as a shockable rhythm and does not respond well to a defibrillator shock.

Imperative Training

As one of the leading providers of First Aid and CPR training in the UK, Imperative Training has been providing learners with life saving skills since 2003.

Equip yourself with the knowledge and confidence to take action if cardiac arrest strikes someone close to you by enrolling on one of our comprehensive courses.

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