Cardioversion
- Professor Mark Westwood, Consultant Cardiologist
Cardioversion is a procedure that helps to get your heart’s rhythm back to normal if it’s beating unevenly or too fast. Cardioversion can treat abnormal heartbeats (arrhythmias) or atrial fibrillation (an irregular and abnormally fast heartbeat). Here we look at a type of cardioversion called electrical or direct-current (DC) cardioversion.
How the heart works
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Your heart is a muscular organ which lies in the centre of your chest.
It pumps blood containing oxygen from the lungs to the body and passes blood without oxygen back to the lungs to absorb more oxygen.
To do this effectively, your heart is divided into four compartments, or chambers.
There are two chambers on the right side of the heart, and two on the left. A valve lies at the exit of each chamber. The valves ensure that blood flows in one direction only.
The left atrium lies above the left ventricle, the two are separated by a valve called the mitral valve.
The right atrium is above the right ventricle, these two chambers are separated by the tricuspid valve.
The left atrium receives blood that contains oxygen from the lungs via the pulmonary veins. This blood then passes into the left ventricle, which pumps it into the aorta.
From the aorta the blood is passed to the different parts of the body.
The right atrium receives blood with little oxygen from the body, via the vena cava. This blood passes into the right ventricle, which pumps it into the pulmonary artery and back to the lungs to have oxygen added to it.
The valve at the exit of the left ventricle, the aortic valve stops blood passing back into the ventricle. The pulmonary valve at the exit of the right ventricle also stops blood flowing backwards.
This flow of blood doesn't happen automatically, it's driven by contractions of the heart muscle which are triggered by electrical impulses.
A pacemaker in the upper part of the right atrium, called the sinoatrial node, sends electrical impulses across the atria that cause them to contract. The impulses reach the atrioventricular node, which is between the right atrium and ventricle, and pass on to the atrioventricular bundle causing the ventricles to contract and send blood to the lungs and around the body.
These electrical impulses spread across the heart muscle to ensure it contracts in the correct sequence. Nerves supplying the heart change the rate at which impulses are sent across the heart muscle to meet the needs of the body.
Together the chambers, valves, vessels and electrical impulses enable blood to be pumped around the body effectively, so you get the oxygen you need.
About cardioversion
An abnormal heart rhythm is called an arrhythmia. It happens when the normal electrical signals in your heart don’t work properly and your heart beats too fast, too slow or irregularly.
Cardioversion involves shocking your heart if it’s beating too fast. To get your heart’s rhythm back to normal, an electric shock is delivered to your heart from a machine called a defibrillator. For this procedure, you’ll be asleep with a general anaesthetic or heavily sedated.
A cardioversion procedure can treat different types of arrhythmia including:
- atrial fibrillation
- atrial flutter
- ventricular tachycardia
- how long you’ve had the arrhythmia
- your symptoms
- your medical history
Cardioversion usually works well, but it isn’t suitable for everyone. Ask your doctor if it’s an option for you. Whether or not it’s right for you may depend on:
Preparation for cardioversion
Preparation for an urgent cardioversion
If you need to have cardioversion urgently, there may be nothing you need to do to get ready for it.
A doctor may give you a medicine (called an anticoagulant) that stops your blood clotting. You’re likely to have this through a drip into a vein in your hand or arm.
You may also have a scan called a transoesophageal echocardiogram to check for blood clots in your heart. An ultrasound sensor is put into your oesophagus (gullet) to look at your heart. Your oesophagus is the pipe that goes from your mouth to your stomach. You’ll have cardioversion as soon as your doctor has checked it’s safe to go ahead.
Preparation for a planned cardioversion
If your cardioversion is planned, there’ll be time for you to take any medicines your doctor prescribes before the procedure. They may prescribe:
- oral anticoagulant medicines – these are tablets that help stop your blood clotting
- anti-arrhythmic medicines – these help to control your heart’s rhythm, which means the cardioversion is more likely to work
- Blood tests – these will check for lots of things, including how well your blood clots.
- An echocardiogram – this is an ultrasound scan of your heart. It provides a clear image of your heart muscles and valves, and shows how well your heart is working.
- A transoesophageal echocardiogram – this is a scan to check for blood clots in your heart.
You may need to take these medicines for several weeks before and after your cardioversion. You will have some tests in hospital before cardioversion. These will help your doctor decide if cardioversion is right for you. You will have an electrocardiogram (ECG), which measures the electrical activity in your heart and its rhythm. You may also have the following tests.
A planned cardioversion is done as a day-case procedure. This means you’ll probably be able to go home on the same day, but it’s possible you may need to stay in hospital overnight. You usually can’t eat or drink on the day of your cardioversion, but follow your doctor’s advice.
Don’t put any powders, lotions or creams on your chest for 24 hours before your cardioversion. These can cause problems with the paddles used for passing the electrical current. If you have any chest hair where the paddles will go, a doctor or nurse may shave it off. You’ll be asked to remove any jewellery before your cardioversion.
Your doctor will discuss with you what will happen before, during and after your procedure. If you’re unsure about anything, don’t be afraid to ask. No question is too small. It’s important that you feel fully informed, so you feel happy to give your consent for the procedure to go ahead.
Ask a friend or relative to drive you home and stay with you after your cardioversion.
Cardioversion procedure
Cardioversion usually takes up to 30 minutes. You’ll be given a sedative or a short-acting general anaesthetic so you’ll be asleep during the procedure.
Your doctor will put two pads (electrodes) on the upper right and lower left of your chest. Sometimes the pads may be put on the front and back of your chest instead. These pads are linked to a defibrillator machine. They’ll give your heart a brief, controlled electric shock in time with the beat of your heart. The electric shock works across your whole heart at once to re-set your heart rate and rhythm back to normal.
Your doctor will monitor your heart rate and rhythm during the procedure. This means they can see straightaway whether the procedure has reset your heart to its normal rhythm. Your doctor may give you one or two more electric shocks to reset your heart if the first one doesn’t work properly.
Aftercare following cardioversion
When you wake up after cardioversion, you may feel tired or unsteady. You’ll need to rest for a few hours until the anaesthetic or sedation has worn off. Your hospital team will let you know when you can go home.
The doctors and nurses will use an ECG machine to monitor your heartbeat. Once they’re happy you’re recovering well and you feel ready, you can get out of bed and walk around.
You’ll probably be given a date for a follow-up appointment before you leave. Your doctor will usually prescribe anticoagulant and anti-arrhythmia medicines for you to take at home.
If you were given anticoagulants before your procedure to thin your blood, you need to continue taking them at home as well.
Arrange for someone to drive you home. General anaesthesia and sedation can make it harder to coordinate your movements and to think clearly. So, it’s a good idea to ask someone to stay with you for the first 24 hours. Don’t drive, look after children, cook, drink alcohol, operate machinery or sign legal documents during this time.
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Recovery following cardioversion
Take it easy for a few days after your procedure. Your doctor will give you advice about what to do. If the paddles have made your skin a little sore (like you have sunburn), you may need to use some creams. Your doctor will usually tell you what to use. They’ll also give you advice about when you can go back to work and start exercising again.
It’s important to keep taking any medicines for as long as your doctor recommends. Anticoagulant medicines will lower your chances of getting a blood clot. You may also need to take anti-arrhythmic medicines – for example, amiodarone – for a while after your cardioversion. This will help to keep your heart rate stable. If you have any questions about your medicines or how to take them, ask a pharmacist.
You’ll have check-ups with your doctor after cardioversion. The first will be around three months after cardioversion.
Contact your GP if you notice any changes in your heartbeat or if your symptoms come back. If your abnormal heart rhythm comes back after you’ve had cardioversion, you may need more treatment. Your doctor may recommend you have cardioversion again. But usually after two or three cardioversions, your doctor may recommend that you have a different treatment, such as medicines or ablation.
Side-effects of cardioversion
Side-effects are unwanted, but mostly temporary, effects you may get after having a procedure. After cardioversion you may:
- notice your chest feels a bit sore where you had the shock
- have some burns on the skin on your chest
- have a headache or feel dizzy if your blood pressure dropped for a while during the procedure
Some of the medicines you’re given to take before or after your cardioversion can have some side-effects too. Ask your doctor about any risks or side-effects of medicines they recommend for you.
Complications of cardioversion
Cardioversion is usually a safe procedure, but sometimes it can cause complications.
In some people, cardioversion doesn’t work or their symptoms come back again. Cardioversion may cause other problems with your heart rhythm. You may need to take a medicine to treat this.
You may get a blood clot. Having a blood clot after cardioversion for some types of arrhythmia can make you more likely to have a stroke. But your doctor may prescribe anticoagulant medicines before and after your procedure to reduce the chances of this happening.
Alternatives to cardioversion
- This information is about electrical or DC cardioversion. Chemical (or pharmacological) cardioversion is when your doctor gives you medicines to bring back your regular heart rhythm rather than using electricity. Ask your doctor if this could be an option for you, and what it involves. A pharmacological cardioversion procedure should be the same as an electrical cardioversion procedure. Your doctor may suggest other treatments to help regulate your heart’s rate and rhythm. The best one for you will depend on the type of arrhythmia you have and your general health.
- Anti-arrhythmic medicines – you must take these tablets long-term to help control your heart’s rate and rhythm. Your doctor may also offer you anticoagulant medicines to prevent blood clots.
- Ablation – this procedure involves putting a thin tube through one of your veins (often in your groin) to reach into your heart. The area of your heart muscle that’s causing the abnormal heart rate is then heated or frozen to form a scar. This scar doesn’t conduct electricity, so it stops any abnormal electrical signals.
- Pacemaker – if you have this device fitted, it can regulate your heartbeat if you have a slow heart rhythm. It’s often an option if medicines haven’t worked for you.
Speak to your doctor about whether or not any of these treatment options are right for you.
Cardioversion is usually a safe procedure with a low risk of complications. But sometimes it can cause other problems with your heart’s rhythm. Very rarely, it can cause blood clots, which increase the risk of having a stroke.
For more information, see our section on complications of cardioversion.
You’ll usually feel back to normal after a few hours, once the anaesthetic or sedative has worn off. You can usually go home from hospital on the same day. Take it easy for a few days after your procedure.
For more information, see our section on recovery following cardioversion.
You won’t be awake during cardioversion. You’ll have a sedative or a short-acting general anaesthetic first.
For more information, see our section on cardioversion procedure
Cardioversion will restore regular heart rhythm in 90 out of every 100 people with atrial fibrillation who have the procedure. But sometimes the symptoms come back. The success rate depends on such things as how old you are, how long you’ve had symptoms, and if you have any other health problems. If your heart rhythm is still irregular after cardioversion, your doctor may suggest you take an anti-arrhythmic medicine.
Echocardiogram
Electrocardiogram (ECG)
An electrocardiogram (ECG) is a test that can record the rhythm and electrical activity of your heart to find out if it’s healthy.
Ventricular tachycardia
Ventricular tachycardia is a type of abnormal heart rhythm (arrhythmia) in which your heart beats too fast.
Other helpful websites
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- Personal communication by Professor Mark Westwood, Consultant Cardiologist, February 2025
- Victoria Goldman, Freelance Health Editor
