Heart Health

Updated 24 August 2017

Cardioversion and defibrillation

What happens during defibrillation and cardioversion?

Electrical cardioversion and defribrillation remain the most reliable methods for stopping arrhythmias.

What happens?
The defibrillator consists of two paddles, 12cm in diameter, which are placed in firm contact with the chest wall. One paddle is placed to the right of the breast bone (sternum) at the level of the second rib. The other paddle is placed on the left side of the chest at the level of the fifth rib centrally between the breast bone and the end of the collar bone (clavicle). The paddles are connected to a device which delivers an electrical current at varying energies.

If the patient is awake, a short-acting sedative is given to prevent discomfort.

An anaesthetist who is skilled at keeping the airway open should be present.

The shock is only given with a certain tracing on the ECG, except in cases of ventricular flutter (VF) or ventricular fibrillation (VF). This is because shocks in the wrong part of the heart cycle can actually produce ventricular fibrillation. In the case of VF or VT, the heart rhythm is so disturbed that the shock will restore regular rhythm.

The amount of energy delivered varies according to the type of arrhythmia. If the first attempt at defibrillation fails, all repeated attempts should be at the maximum energy that the defibrillator can deliver.

When is cardioversion used?
Any tachycardia other than a normal fast heart beat due to exercise, excitement etc, which produces... :

  • very low blood pressure (hypotension)
  • lack of blood and oxygen to the heart muscle (myocardial ischaemia)
  • heart failure

... requires immediate termination using cardioversion with a defibrillator.

Arrhythmias that have not stopped with medical management can also be stopped using cardioversion.

After someone has been cardioverted, there are often transient arrythmias, commonly slowing of the heart or short runs of fast heart beats. These are common and do not need to be treated.

 - (Health24, updated June 2008)


Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.