What is cardioversion, and what is defibrillation?

Image by National Heart Lung and Blood Institute.

Simply put, this is where electricity is delivered through your heart to get your heart back into a normal rhythm.

The heart relies on an electrical system to regulate its beating pattern. This electrical signal starts at the sinoatrial node, passes through the atria (the top chambers) then pauses at the atrioventricular node, and ends in the ventricles (the bottom chambers). This normal rhythm is called sinus rhythm. This rhythm is regular, and changes speed based on your physical activity.

Sometimes the body can go into a different rhythm, some of which are dangerous.

The most common abnormal rhythm (arrhythmia) is atrial fibrillation (AF). In this rhythm, there are many disorganised electrical signals coming from the atria, which can cause the lower chambers to respond erratically, giving you an irregular rhythm. AF is not life threatening, but can give you palpitations and shortness of breath, and also carries a risk of stroke.

If the lower chambers – ventricles – go into an abnormal rhythm, it can be life threatening. Ventricular arrhythmias, such as ventricular tachycardia and ventricular fibrillation, stop your heart from working effectively and require immediate treatment.

To get your body back into normal rhythm, there are two options, cardioversion and defibrillation. Both involve the delivery of electrical energy through adhesive pads into your chest while you are sedated.

The pads applied to your chest and/or back for cardioversion and defibrillation.

Cardioversion (often called DCR)

Cardioversion is for a non-urgent rhythm, most commonly atrial fibrillation or atrial flutter. If it is for AF or flutter, it is critical that you have been taking your blood thinner (anticoagulant) for at least 4 weeks prior to the procedure, and you haven’t missed any doses. If there is a problem here, you could be at risk of a stroke, so please notify your doctor before going ahead. All of your medications can continue, including on the day of the procedure (with a small sip of water in the morning).

Here, you are admitted to hospital as a day case, and a drip is inserted into your arm. An anaesthetist will discuss your medical history with you and you will be changed into a patient gown for your top half. Any rings, necklaces and metallic jewellery should be removed. A nurse or doctor will apply the pads to your chest – these are large adhesive patches that are either applied to the front and side of your chest, or to your chest and back. You are given a sedation medication (you are still breathing, but not conscious), and once you are asleep, the machine is charged and the electricity is given through the pads to get your heart back into normal rhythm.

Getting good contact with the pads is essential, so your chest may be shaved. The position of the pads is also critical so the nurse or doctor may have to loosen your gown and expose your chest to apply the pads correctly. Usually, three attempts will be made to get you back into your normal rhythm. Once you wake up from the sedation, you will be able to go home later that day (usually between two to four hours afterwards). An ECG will be performed to confirm if you have stayed back in your normal rhythm. You will need someone to pick you up as you cannot drive after receiving the sedation medication.

Ensure that you have an appointment to see your usual cardiologist four to six weeks after your cardioversion, regardless of whether it was successful or not. You must continue taking your blood thinner (anticoagulant) after the procedure, as there is a slightly higher risk of stroke for four weeks afterwards.


Defibrillation is very similar – electrical energy is delivered to your heart – but this is for a more urgent situation. Pads are put on the chest and the same machine is used to give you the energy. Because this is an emergency, and blood is not pumping around your body, you may be unconscious, and as a result sedation medication is rarely given.

Cardioversion vs. defibrillation

Other than urgency, the key technical difference between cardioversion and defibrillation is the timing of the electrical delivery. In cardioversion, the electricity is given at a very specific point in your heart’s electrical cycle to reduce the risk of being put into a more dangerous rhythm. In defibrillation, the rhythm is too disorganised to be read by the machine to set the timing, and the energy is given as soon as possible.




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