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Atrial fibrillation treatments


What is cardioversion?

A cardioversion is a treatment which delivers electrical energy (shock) to the heart using an external defibrillator to get the heart back into sinus rhythm. This is done by attaching electrodes (sticky pads) to the chest to deliver the electric shock.

Cardioversion is very quick and can be very effective in many patients. In some patients, sinus rhythm can be maintained for several years and in others it can be much shorter. The length of time your sinus rhythm is maintained will depend on how long you have been in atrial fibrillation (AF) and other factors, such as how large your left atrium is. 

Cardioversion and anticoagulants

Once you have been referred for this treatment it is important to ensure you have been adequately anticoagulated (with warfarin or a newer anticoagulant) for at least three weeks before the procedure.

If you are taking warfarin then you will need weekly INR levels between two and three for at least three consecutive weeks leading up to the planned cardioversion. If the levels have fallen below two prior to your cardioversion, you are at increased risk of a stroke and your procedure will need to be delayed. 

After the cardioversion you will need to continue your warfarin for at least four weeks, or indefinitely if you have a CHA2DS2VASc score of less than one. This will be reviewed at your next clinic appointment.

If you are taking one of the newer oral anticoagulants (dabigatran, rivaroxaban or apixaban) then you will need to take these as instructed for at least three weeks before the cardioversion. It is very important that you do not miss any doses of your anticoagulant as your risk of stroke will be increased and your procedure will need to be delayed.

As we do not routinely monitor the drug effects in patients taking a NOAC, we recommend you undergo a procedure at the start of your cardioversion called a transoesphageal echocardiogram (or TOE) to exclude a clot. This involves placing a probe into your food pipe (oesophagus) to take an ultrasound scan of your heart. 

If a clot is found in your left-atrial appendage, your cardioversion will be cancelled. The TOE will be done at the start of the cardioversion and you will be under a general anaesthetic when this is performed. You will probably find that your throat may be sore after the procedure. The TOE is generally safe but can cause damage to the food pipe in rare cases (one in 5,000) or to teeth. 

You should continue on all your medications unless instructed otherwise. In some cases, patients may be asked not to take their beta blockers / calcium channel blockers on the morning of their cardioversion to avoid bradycardia (slow heart rate) following the procedure.

The procedure

You will be admitted to the day case unit/cardiology ward on the morning of your cardioversion. A doctor/clinical nurse specialist will take a full medical history, blood tests including your INR levels, and examine you to ensure you are fit for the procedure. 


An ECG (electrocardiogram) will be taken to confirm that the arrhythmia is still present. The procedure will be explained to you and you will be asked to sign a consent form.

Once we have confirmed that you are ready for the procedure, you will be taken to another department. You will be met by the anaesthetist and a doctor/nurse who will explain what they are going to do. 

Two electrode patches will be placed on the upper right and lower left side of the chest, or your front and back, and this will be attached to the defibrillator. A cannula (small needle) will be put in the back of your hand or in your arm. You will be given a short general anaesthetic to put you to sleep. 

The defibrillator is then charged and ready to deliver a shock. One shock can be sufficient to restore sinus rhythm. However, a small number of people may require further shocks and a small percentage of patients will remain in AF despite several attempts.

Like any intervention there are possible risks. These include:

  • Stroke - this is rare if the INR levels have been within the therapeutic range of 2 to 3 for at least three consecutive weeks

  • Bradycardia - this is normally very brief following the cardioversion. A small percentage of patients may require intravenous medication or external pacing of the heart via the two electrodes that delivered the shock. In very rare cases, a permanent pacemaker may be required.

  • Ventricular tachycardia - this is rare but can occur following the initial shock and would require a further shock to establish sinus rhythm.

  • Skin burns from the electrode pads - should this occur you will be given a cream to apply to the affected areas.


After the procedure

You will be taken back to the day-case unit/ward to recover. You will be monitored for at least two hours before being allowed to go home. An ECG will be taken before you are discharged to make you have remained in sinus rhythm. 

You will need someone to collect you, as you are not allowed to drive for 24 hours following this procedure.

You will be seen in clinic by either your doctor or clinical nurse specialist approximately three months after your cardioversion. 

If your discharge ECG shows AF, you will be booked back into clinic earlier to discuss further treatment options.  


Hill End Road, Harefield,
Middlesex, UB9 6JH
Tel: +44(0)1895 82 37 37

Royal Brompton

Contact our AF team

Harefield Hospital

01895 828979

Royal Brompton Hospital

020 7351 8364