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Supraventricular tachycardia (SVT) is an abnormally fast heart rate of over 100 heartbeats a minute.
You'll usually feel your heart suddenly start racing and going very fast, then stop or slow down abruptly. You may also experience:
Episodes of SVT can last for seconds, minutes, hours or even days, in rare cases. They may occur several times a day, or only once or twice a year.
Read more about the symptoms of SVT.
SVT is rarely life-threatening, but you should contact your GP as soon as possible, if you experience symptoms.
A test called an electrocardiogram (ECG) can be used to confirm a diagnosis of SVT, if the heart is still racing. Occasionally, an ECG can show abnormalities that suggest you have SVT, even when your heart rhythm returns to normal.
As SVT can sometimes be difficult to diagnose, your GP may refer you to a cardiologist (heart specialist) who specialises in treating heart rhythm disorders, called an electrophysiologist.
Dial 999 to request an ambulance if you experience severe chest pain or breathing difficulties and you feel faint.
Read more about diagnosing SVT.
SVT occurs when there's a problem with the heart's electrical system, which controls your heart rhythm. This causes the heart to beat much faster than normal.
In some people, SVT results from an extra electrical connection in the heart present from birth (Wolff-Parkinson-White syndrome), but it can also occur in hearts that are otherwise normal.
SVT can occur in anyone at any age and often starts for the first time in children or young adults. Generally, the fast heart rate happens more frequently and lasts longer the older you get.
SVT can be triggered by the extra heartbeats (ectopic heartbeats) that most people experience, but some episodes are brought on by things like drinking large amounts of alcohol or caffeine, stress, or smoking lots of cigarettes.
Read more about the causes of SVT.
Most episodes of SVT are harmless, don't last long and settle on their own without treatment. However, the symptoms are often troublesome and treatments are available to stop ongoing episodes and prevent them occurring in the future.
Ongoing episodes of SVT can sometimes be stopped using certain manoeuvres, such as the Valsalva manoeuvre, that slow down the electrical impulses in the heart by stimulating a nerve called the vagus nerve. The Valsalva manoeuvre usually involves holding your nose, closing your mouth and trying to exhale hard, while straining as if you were on the toilet.
If manoeuvres like this are ineffective, injections of medication or an electric shock treatment called cardioversion can usually help to stop ongoing SVT episodes.
To prevent future episodes, medication that's taken every day can be prescribed. However, the definitive treatment is a procedure called catheter ablation, which involves destroying the tiny areas of the heart that are causing problems. It's very effective at preventing future episodes.
Read more about treating SVT.
If you have supraventricular tachycardia (SVT), you'll usually have episodes where you feel your heart beating very quickly.
Even though your heart is beating faster, the gaps between heartbeats should still be regular. If your heartbeat is fast and irregular, it's more likely that you have a different heart rhythm problem, called atrial fibrillation.
Other symptoms of SVT include:
In rare cases, fainting may be another symptom you experience as a result of a fall in blood pressure. If you do faint and experience heart palpitations (noticeable heartbeats) before the faint, you should seek medical attention straight away.
Symptoms of SVT can last for seconds, minutes, hours or longer (in rare cases). Some people have symptoms several times a day, whereas others may only experience episodes once or twice a year.
SVT is rarely life-threatening. However, you should contact your GP as soon as possible if you experience a rapid heartbeat and any of the above symptoms because other, more serious, life-threatening conditions can have similar symptoms.
Dial 999 to request an ambulance if you experience severe chest pain or breathing difficulties and you feel faint.
Supraventricular tachycardia (SVT) is caused by a problem with electrical impulses in the heart.
Heartbeats are normally initiated by a small group of cells at the top of the heart called the sinoatrial node, which acts as the heart's natural pacemaker.
The sinoatrial node produces electrical signals that pass through the muscles of the upper heart chambers (atria), causing them to contract and pump blood into the lower heart chambers (ventricles).
The signal then passes into another group of cells in the middle of the heart called the atrioventricular (AV) node. From here, the signals travel into the ventricle muscles, causing them to contract and pump blood out of the heart.
Episodes of SVT occur when a problem develops in this system. This causes faster signals to be sent around the heart, increasing the speed at which the heart beats.
In most cases, the problem is temporary and lasts for a few seconds, minutes, or in some cases hours.
There are several different types of SVT, which are classified by the specific problem in the heart that disrupts the electrical system.
A type of SVT called Wolff-Parkinson-White syndrome occurs as a result of an abnormal electrical connection between the atria and ventricles, which creates a short circuit in the heart's electrical system. This happens because people with Wolff-Parkinson-White syndrome are born with an extra strand of muscle tissue between these chambers.
In other cases of SVT, a short circuit occurs, even though the heart is otherwise normal.
SVT can also be caused by an electrical signal from another part of the heart overriding the signal from the sinoatrial node.
SVT is usually triggered by extra heartbeats (ectopic beats), which everyone has. It may also be triggered by:
However, in the majority of cases, there's no identifiable trigger for SVT.
Your GP may suspect you have supraventricular tachycardia (SVT) from a description of your symptoms.
If so, you may be asked to have an electrocardiogram (ECG) or be referred to a cardiologist who specialises in heart rhythm disorders and abnormal heart beats (an electrophysiologist).
An ECG is a test that records the heart's rhythm and electrical activity. It's a painless procedure that's usually carried out in hospital or in your GP surgery, and takes about five minutes to complete.
Small stickers (electrodes) are stuck to your arms, legs and chest and connected via wires to an ECG machine. Every time your heart beats, it produces tiny electrical signals. An ECG machine traces these signals onto paper.
During an episode of SVT, your heart rate will usually be between 140 and 250 beats per minute (bpm), compared to a normal heartbeat of 60-100bpm.
If the test is carried out while you're having an episode of SVT, the ECG will record your abnormal heart rate. This will confirm SVT and rule out other conditions.
However, it may be difficult to capture an episode, so your doctor may ask you to wear a small, portable ECG monitor to record your heart rate, either continuously over 24 or 48 hours, or from when you switch it on at the start of an episode. Some monitors can be worn for a week or longer.
Further tests may be carried out once SVT has been confirmed. These will help to determine the exact location of the problem in heart.
For example, you may be asked to take part in an electrophysiology study carried out under sedation, where soft, flexible wires are passed up a vein in your leg and into your heart. The wires measure the electrical signals in your heart and allow doctors to locate the problem.
In many cases, symptoms of supraventricular tachycardia (SVT) stop quickly and no treatment is needed.
However, if necessary, treatment is available to stop an episode of SVT and prevent future episodes.
The various treatments for SVT are outlined below. You can also read a summary of the pros and cons of the treatments for SVT, allowing you to compare your treatment options.
Vagal manoeuvres are techniques designed to stimulate the vagus nerve. Stimulating this nerve can reduce the speed of the electrical impulses in your heart and stop episodes of SVT. However, these techniques work in less than one in three cases.
One of the main vagal manoeuvres used is called the Valsalva manoeuvre. There's no standard way to perform this manoeuvre, but it often involves holding your nose, closing your mouth and trying to exhale hard while straining as if you were on the toilet. If you're in hospital, you may be asked to blow hard into a tube instead.
You can perform a simple version of the Valsalva manoeuvre at home to try to stop an episode of SVT. You can also try dipping your face into a bowl of cold water, as this can have a similar effect.
An alternative vagal manoeuvre is a carotid sinus massage. This involves massaging an area of your neck called the carotid sinus in an attempt to stimulate the vagus nerve. However, this should only be carried out by a healthcare professional and shouldn't be attempted at home. For more information, you can read the NHS leaflet about carotid sinus massage.
If vagal manoeuvres are unsuccessful, you may need an injection of a medication called adenosine in hospital. This medication blocks the abnormal electrical impulses in your heart.
An injection of verapamil may sometimes be used instead of adenosine, but only usually if adenosine is unsuitable (for example, if you have asthma). This is because there's a risk of more serious side effects, including low blood pressure.
If a prolonged episode of SVT doesn't respond to vagal manoeuvres or medication, or if these treatments are unsuitable, a treatment called cardioversion may be used.
Cardioversion is a relatively simple procedure that uses a defibrillator to apply an electrical current to your chest. This shocks the heart back into a normal rhythm.
It's usually carried out under general anaesthetic and you should be able to go home the same day.
Cardioversion is a very effective procedure and serious complications are uncommon. However, your chest muscles may feel sore afterwards and the areas of skin where the electrical shocks were applied may be red and irritated for a few days.
There are also some treatments that reduce your chances of having further SVT episodes.
Some SVT episodes are triggered by things like tiredness, drinking lots of alcohol or caffeine, or smoking lots of cigarettes.
Cutting down on the amount of caffeine or alcohol you drink, stopping or limiting how many cigarettes you smoke, and making sure you get enough rest can reduce your chances of having further episodes.
If necessary, medication can be prescribed to prevent further episodes of SVT by slowing down the electrical impulses in your heart. These medications are taken as a daily tablet and include digoxin, verapamil and beta-blockers.
Common side effects of these medications can include dizziness, diarrhoea and blurred vision. Tiredness can occur with beta-blockers and men may experience problems getting erections. Less common side effects include difficulty getting to sleep (insomnia) and depression.
If the medication you're prescribed doesn't work or has unpleasant side effects, a more suitable alternative can often be found.
If you have repeated episodes of SVT, an operation called catheter ablation is the recommended treatment option. This prevents further episodes of SVT by destroying the tiny parts of the heart causing the problems in the heart's electrical system.
Catheter ablation is a safe and highly effective treatment, and means you no longer need to take medication. It cures SVT in over 95% of people and is the recommended treatment worldwide.
During catheter ablation, a thin wire called a catheter is inserted into a vein in your upper leg or groin, before being guided to your heart by an electrophysiologist (a heart specialist who specialises in abnormal heartbeats and rhythms). When the wire reaches the heart, it records the electrical activity to pinpoint the precise location of the problem.
When the problem area is found, high-frequency radiowaves are transmitted to the catheter tip to destroy it, producing a small scar.
You'll remain awake during this procedure, but will be given a sedative to relax you. Local anaesthetic will be used to numb the area where the catheter is inserted.
The procedure lasts about an hour and a half and you can usually go home on the same day you have the procedure. However, there may be instances where you need to stay in hospital overnight – for example, if you're operated on in the late afternoon.
Catheter ablation is very effective at preventing future episodes of SVT (19 out of every 20 people treated will never have the problem again), but like all operations it carries a risk of complications. These include bruising and bleeding where the catheter was inserted. Any bruising will usually be small, but even if you have a large bruise it won't require any treatment and will disappear within two weeks.
There's also a small risk (less than 1 in 100) of the heart's normal electrical system being damaged. This is known as heart block, and if it happens you may need a permanent pacemaker to control your heart rhythm.
You should discuss potential benefits and risks of catheter ablation with your surgeon (the electrophysiologist) before the procedure.