Supraventricular tachycardia (SVT)

Supraventricular tachycardia (SVT) is a type of abnormal heartbeat (arrhythmia) in which your heart beats too fast. It’s caused by faulty electrical signals in your heart – electrical impulses don’t travel normally from the top chambers to the bottom chambers of your heart.

About supraventricular tachycardia (SVT)

SVT is the term used when your heart beats faster than normal because of a problem that happens above the lower chambers of your heart (ventricles). Your heartbeat is controlled by electrical signals (impulses) that travel through your heart and make it contract.

Watch our animation to see how your heart beats normally and what happens in SVT.

SVT is often caused by an extra electrical pathway (or pathways) in your heart between your atria (the top chambers of your heart) and your ventricles. This can make the electrical signals form a short circuit between the top and bottom chambers.

Normally, your heart beats between 60 and 100 times a minute when you’re resting. With SVT, you usually get episodes where your heart suddenly starts beating faster (paroxysmal supraventricular tachycardia). During an episode of SVT, your heart may beat between 140 to 250 beats per minute. These episodes can last anywhere from a few seconds to several hours or, rarely, for more than 12 hours, before going back to normal.

SVT can affect you at any age, even if you’re young and otherwise healthy. Most people are diagnosed in early childhood or in their early 20s or in their 40s – it depends on which type of SVT they have.

Types of supraventricular tachycardia (SVT)

There are several different types of SVT. Three common types are sinus tachycardia, Wolff–Parkinson–White (WPW) syndrome and atrio-ventricular nodal reciprocating tachycardia (AVNRT).

Sinus tachycardia

Sinus tachycardia means your heart beats in a normal, regular rhythm, but faster than normal. It's usually a normal response to changes in your body. It isn’t caused by a problem with the electrical signals in your heart. Your heart rate may increase when you’re pregnant, do strenuous exercise, or feel stressed or anxious. It may also increase if you have caffeine or alcohol or take certain medicines or illegal drugs. Some medical conditions, such as an overactive thyroid gland (hyperthyroidism) or anaemia (a lack of iron), may increase your heart rate too.

Wolff–Parkinson–White (WPW) syndrome

WPW syndrome is caused by an extra electrical pathway between the atria and ventricles in your heart. The electrical impulses pass through your heart more quickly than normal and can also travel in the opposite direction. The extra pathway can lead to atrial fibrillation (when your atria start beating out of control) as well as SVT. WPW syndrome is usually something you’re born with – but you may not notice any problems until you’re much older.

Atrio-ventricular nodal reentrant tachycardia (AVNRT)

AVNRT is caused by more than one connection to the atrio-ventricular node, which acts like a junction box and is between your atria and ventricles. This extra, faster circuit results in more heartbeats than normal

Causes of supraventricular tachycardia (SVT)

SVT is usually due to extra pathways between the upper and lower chambers of your heart (the atria and ventricles). There’s no specific supraventricular tachycardia cause because you’re normally born with it.

Most people with SVT don’t have any underlying problem with their heart or a health condition that causes SVT. But sometimes, other problems that affect your heart, such as a previous heart attack or surgery on your heart, can lead to SVT.

If you get SVT, you might find that various things trigger it. These may include:

• some types of medicines
• drinking alcohol
• caffeine
• smoking
• stress – either physical after you’ve been exercising, or emotional
• taking illegal drugs, such as cocaine or speed

Symptoms of supraventricular tachycardia (SVT)

SVT doesn’t always cause symptoms. But this depends on several things, including how long the episode of SVT lasts and how fast your heart rate is.

If you do get SVT symptoms, you may:

• get palpitations, when you can sense your heart thumping, fluttering, or skipping beats
• feel lightheaded and dizzy
• have a pounding feeling in your neck
• feel short of breath
• get anxiety
• have chest pain or discomfort
• pass out (but this isn’t common)

If you get any of these supraventricular tachycardia symptoms and they’re relatively mild, go and see your GP. If you’ve already been diagnosed with SVT, you may be able to stop the symptoms yourself. For more information, see our section on treatment of supraventricular tachycardia (SVT). If you feel like you may collapse and need urgent medical care, go to your nearest accident and emergency department.

More serious problems are rare with SVT but can happen with a particular type of SVT called Wolff–Parkinson–White (WPW) syndrome.

Diagnosis of supraventricular tachycardia (SVT)

Your GP will ask about your symptoms and examine you. They’ll want to know how often you have symptoms, what they feel like and if anything in particular seems to set them off. They’ll check your blood pressure, listen to your heartbeat and take your pulse. They’ll also ask about your medical history and your family history as well.

You’ll need to have a test called an electrocardiogram (ECG) to record the electrical activity in your heart.

Your GP may refer you to a cardiologist (a heart specialist) for more tests. This may be someone who specialises in heart rhythm disorders (an electrophysiologist).

You may be offered an ambulatory ECG, which records your heartbeat while you go about your usual activities over 24 hours or more. Or you may have an implantable loop recorder. This is a small device that’s implanted under your skin and is programmed to record abnormal rhythms.

Your GP or cardiologist may also arrange for you to have some of the following tests.

• Blood tests. These will check for substances that may be causing SVT, and for other conditions that may be causing your symptoms.
• Echocardiogram. This test uses ultrasound to provide a clear image of your heart muscles and valves and can show how well your heart is working. It can also help show if it’s likely that you have an abnormal heart rhythm.
• Exercise ECG (cardiac stress test). This is when you have an ECG while you exercise on a treadmill to see if this triggers an arrhythmia.
• Chest X-ray. This will allow your doctor to look for any changes in your heart or lungs that may be causing the problem.

If you measure your own pulse, it could be useful because it may help your doctor to see what happens when you have an attack. Devices such as smart watches and phones can help you monitor your symptoms. Ask your doctor about using these.

Treatment of supraventricular tachycardia (SVT)

SVT treatment is aimed at stopping attacks and controlling your heart rhythm and rate to prevent further attacks. Which treatment you’re offered will depend on:

• the type of SVT you have
• how often you get symptoms
• how severe they are
• how long they last

Your doctor will discuss your SVT treatment options with you.

Stopping an attack

If you see a doctor while you’re having symptoms of SVT, they may need to give you treatment to stop the attack. This could include one of the following options.

• Your doctor may apply pressure to an artery in your neck. For some types of SVT, this can help stop your heart beating so rapidly.
• Valsalva manoeuvre. This involves breathing out through your mouth while pinching your nose. This increases the pressure in your chest and can put your heart back into its normal rhythm.
• Antiarrhythmic medicines, such as adenosine, or verapamil through a drip into your bloodstream. Verapamil and beta-blockers can also be taken as tablets, as can a medicine called flecainide. These are useful as a ‘pill in the pocket’ strategy that you can take when you need to.
• Electrical cardioversion. This uses an electric shock to restore your rapid heartbeat to normal.

Long-term supraventricular tachycardia treatment

Whether or not you need any long-term SVT treatment depends on lots of things. These include:

• the type of SVT you have
• how often you get symptoms
• how long they last
• how they affect you

Catheter (cardiac) ablation for SVT

Your doctor may offer you a procedure called catheter ablation (also called cardiac ablation), especially if you keep having regular attacks of SVT. Catheter ablation can permanently fix the problem if it’s causing you issues. This procedure involves inserting a small tube called an electrode catheter, usually into a vein in your groin, and using X-rays to pass it up to your heart. Radiofrequency waves are then delivered via the catheter to destroy any tissue that’s causing the abnormal electrical signals in your heart.

SVT ablation is usually done under local anaesthesia, sometimes with sedation, to help you to stay relaxed during the procedure. Catheter ablation can be over quickly, or it can take three or four hours. You can usually have the procedure and go home the same day, although sometimes you might need to stay overnight. You should be able to get back to most of your normal activities soon after a catheter ablation, but take it easy for a few days. You may want to take a couple of days off work, especially if you have a physically demanding job. Don’t lift anything heavy for at least two weeks. Ask your doctor when it’s safe for you to drive after catheter ablation as it can depend on the type of procedure you had and what type of vehicle you drive.

Medicines

Your doctor may prescribe you some medicines to stop you having more SVT episodes. These include:

• beta-blockers
• calcium channel blockers
• other antiarrhythmic medicines, such as amiodarone or flecainide

Always read the patient information leaflet that comes with your medicine and ask your pharmacist or doctor if you have any questions. If medicines don’t work, your doctor will usually suggest you have an ablation.