Ventricular Fibrillation and Heart Rhythms

Ventricular Fibrillation

The function of the heart is to continually pump oxygenated blood around the body. The heart itself consists of muscular walled chambers that constrict and expand approximately once every second. These constrictions occur as a result of electrical impulses originating in the heart’s in-built pacemaker and travelling along electrical pathways to all parts of the heart muscle.

If a problem occurs in the heart’s electrical system or there is a disruption of the blood supply to the heart muscle (such as during a heart attack), the normal electrical activity will be disrupted. Once this happens, the correct heart rhythm cannot be maintained so the heart begins to mis-fire electrical signals. The chaotic signals cause the heart chambers to become uncoordinated in their constrictions and effectively quiver rather than beat a steady rhythm. This is called ventricular fibrillation.

Ventricular fibrillation is fatal if untreated as the lower heart chambers contract in a rapid and uncoordinated manner. As a result, the heart doesn’t pump blood to the rest of the body. Immediate medical attention is required, as this is the most frequent cause of sudden cardiac death which can occur in as little as 4 minutes.

Signs & Symptoms

Loss of consciousness is the most common symptom of ventricular fibrillation.
Before a ventricular fibrillation episode, a person may experience an irregularly fast (tachycardia) or erratic heartbeat (arrhythmia). They may also have:

  1. Chest pain
  2. Dizziness
  3. Nausea
  4. Shortness of breath


First aid treatment for ventricular fibrillation includes cardiopulmonary resuscitation (CPR) and shocks to the heart using an automated external defibrillator (AED).

The shock that an AED delivers does not re-start the heart. It polarises (electrically charges) the cells in the cardiac conduction system all at the same time, which stops the ventricular fibrillation. Once the fibrillation is stopped the hearts pacemaker will hopefully be able to resume its normal electrical pulses and start to beat normally again.

Time is crucial when using an AED – the sooner a shock can be delivered the higher the chances of survival.

Heart Rhythms

When an AED is attached to a casualty it will analyse the heart rhythm to see if a shock is advised. If a casualty is in Asystole (no electrical activity detected) the AED will not deliver a shock as the pacemaker has failed.

  • Sinus rhythm – Normal heartbeat
  • Ventricular fibrillation (VF) – Heart is quivering and not pumping blood
  • Ventricular tachycardia (VT) – The heart rate is so fast that the chambers cannot fill with blood.
  • Asystole – No electrical activity in the heart

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