What happens during supraventricular tachycardia?
Your heartbeat is controlled by electrical signals (impulses) that travel through your heart and make it contract.
Supraventricular tachycardia (SVT) is a term for when your heart beats faster than normal because of a problem that happens above your ventricles. Your ventricles are the lower chambers of your heart. Often, there’s an extra electrical pathway (or pathways) in your heart between your atria (the top chambers of your heart) and your ventricles. This acts a little bit like a short circuit.
Watch our animation to see how your heart beats normally and what happens in SVT.
If you have SVT, your heart may beat between 140 to 250 beats per minute. Normally, it beats between 60 and 100 times a minute (when you’re resting).
Symptoms of supraventricular tachycardia
Supraventricular tachycardia (SVT) doesn't always cause symptoms. If you do get any symptoms, they may come and go, and how long they last varies. It can be anything from a few minutes to several months. Often, it starts and then finishes abruptly.
During SVT you may:
- get palpitations (a thumping in your chest)
- feel lightheaded and dizzy
- feel short of breath
- have chest pain
- blackout (but this isn’t common)
If you get any of these symptoms, go and see your GP. If you feel very unwell or you blackout, go to the accident and emergency department at your nearest hospital.
Diagnosis of supraventricular tachycardia
If you’re unsure about any symptoms you’re having, it’s best to go and see your GP to talk them through. Our Cardiology Clinical Adviser, Dr Yassir Javaid, explains why in our video: When should you see a doctor about your heart?
Your GP will ask about your symptoms and examine you. They’ll check your blood pressure, listen to your heartbeat and take your pulse. Your GP will also ask about your medical history.
You may need to have a test called an electrocardiogram (ECG). An ECG records the electrical activity in your heart to see how well it's working. You might need to wear a 24-hour heart monitor, which is called ambulatory ECG. This records the electrical activity of your heart while you go about your usual activities over 24 hours (or longer if necessary). Or you might need to have an implantable loop recorder. This is a small device (about the size of a computer memory stick), which is implanted under the skin. You activate the device when you feel an abnormal rhythm.
If your GP suspects that you have supraventricular tachycardia (SVT), they may refer you to see a cardiologist (heart specialist). Either your GP or your cardiologist will then arrange for you to have some of the following tests.
- Blood tests. These will check for substances that may be causing SVT or other conditions that may be causing your symptoms.
- Electrophysiological study. This checks the electrical activity of your heart to see what’s causing an abnormal heart rhythm.
- Transthoracic 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.
- Exercise ECG (cardiac stress test). This is when you have an ECG while you exercise to see how your heart works under pressure. It may trigger abnormal heart rhythms, but you’re in the best place for this to happen as you’ll be surrounded by a medical team.
- Chest X-ray. This will enable your doctor to look for any changes in your heart or lungs that might be causing the problem.
You might find that some things trigger your SVT, such as if you drink a lot of caffeine or alcohol, or smoke or take illegal drugs. If you can cut down or stop these, they might in turn stop your SVT.
Your doctor will give you some advice on things you can do to stop an episode. These might include the options below – try to do them as soon as you notice your symptoms.
- Valsalva manoeuvre. This involves you lying down on your back and blowing into a syringe for about 15 seconds. This increases the pressure in your chest, which triggers your body to slow your heart rate down.
- Cold water treatment. Fully immerse your face in ice-cold water or drink ice-cold water.
Treatment of supraventricular tachycardia
Treatment for supraventricular tachycardia (SVT) aims to control your heart rhythm and rate. What treatment you have will depend on your symptoms. You may not need any treatment at all; sometimes your symptoms may go away on their own. If your SVT is caused by taking medicines, your doctor can review them. If it’s caused by an underlying health condition, your doctor will focus your treatment on that.
Your doctor will discuss your treatment options with you.
Treatments for SVT in an emergency include medicines (see below) and electrical (DC) cardioversion. This uses an electric shock to restore your rapid heartbeat back to normal. For more information about this, see our separate topic on Cardioversion.
If your doctor applies pressure to an artery in your neck, it may help to stop your heart beating rapidly. As you can imagine, this can be dangerous to do on some people. So your doctor will need to check whether this technique is suitable for you. And they might record your heartbeat with an electrocardiogram (ECG) while they do it.
If your symptoms come on suddenly, your doctor may give you antiarrhythmic medicines, either as tablets or through a drip into your bloodstream. These aim to get your heart rhythm back to normal. There are different types of medicine that can do this, which include beta-blockers, calcium-channel blockers and other antiarrhythmic medicines, such as one called adenosine that you have at hospital though a drip into a vein. This is a type of emergency medicine. You may also take some medicines to prevent further SVT episodes.
Always read the patient information leaflet that comes with your medicine. If you have any questions, ask your pharmacist or doctor for advice.
You might need to have a procedure called catheter ablation to treat SVT, particularly if you get symptoms that keep coming back. In this procedure, your doctor will pass a small tube called an electrode catheter into the vein in your groin. They’ll pass it up to your heart and destroy any tissue that's disrupting or causing abnormal electrical signals. Catheter ablation often works really well – more than nine in 10 patients are cured.
Causes of supraventricular tachycardia
Most people with SVT don’t have any underlying problem with their heart or any health condition that leads to it.
It may be triggered by things, such as:
- taking some types of medicines
- drinking a lot of alcohol
- taking illegal drugs, such as cocaine or speed
However, in some people, supraventricular tachycardia (SVT) happens because there’s an extra electrical connection in the heart that they’re born with. This is called Wolff–Parkinson–White syndrome. To learn more about this, see our FAQ: Wolff–Parkinson–White syndrome below.
Other things that can increase your risk of getting it include:
- having heart muscle disease (cardiomyopathy)
- coronary heart disease
- having had an operation on your heart
- an overactive thyroid (hyperthyroidism)
- lung disease, such as chronic obstructive pulmonary disease (COPD)
- heart valve disease
- problems with your heart that you’ve had since birth (congenital heart disease)
Complications of supraventricular tachycardia
While most people don’t get any complications, it’s possible you could have some from supraventricular tachycardia (SVT) because your heart rate isn't normal. Occasionally if SVT goes on for a long time and you have other issues, you may be at risk of:
You also have a small risk of sudden death, but usually only if you have a particular type of SVT called Wolff–Parkinson–White syndrome. And your doctor will do everything they can to lower this risk. For more information, see our FAQ: Wolff–Parkinson–White syndrome.
FAQ: How long does it take to recover from catheter ablation?
Catheter ablation is a procedure to treat SVT, in which your doctor will pass a small tube called an electrode catheter into the vein in your groin. They’ll pass it up to your heart and destroy any tissue that's disrupting or causing abnormal electrical signals. It’s a minimally invasive procedure, which means your doctor will make only a small puncture in your groin. Most people recover quickly – you should be able to go home on the same day as the procedure, or the day after.
You may feel aware of your heartbeat after having catheter ablation but this should go away in time. Take it easy for a few days after having catheter ablation. Don't drive for two days, and don’t lift anything heavy for at least two weeks.
FAQ: What’s sinus tachycardia?
Sinus tachycardia means your heart beats in a normal, regular rhythm, but faster than usual. Your heart normally beats at between 60 and 100 times a minute (when you’re resting). If you have sinus tachycardia, it beats at over 100 beats a minute. It's different to supraventricular tachycardia (SVT) because it’s a normal response to changes in your body. It isn’t usually caused by a problem with the electrical signals in your heart.
Your heart can sometimes beat faster than normal in response to your environment or situation. Your heart rate will speed up when you:
- do some strenuous exercise
- feel stressed or anxious
- are in pain, or are ill
- take some types of medicines
- take some types of illegal drugs (such as cocaine and speed)
- have caffeine or alcohol (especially if you have a lot)
Some medical conditions, such as an overactive thyroid gland (hyperthyroidism) or anaemia, can increase your heart rate too.
Most people don't need treatment for sinus tachycardia because their heartbeat doesn’t stay raised for long and soon returns to normal. But if it's caused by an underlying health condition, your GP will focus on treating it.
Inappropriate sinus tachycardia is when your heart beats faster than usual for no apparent reason. This may be because you’re abnormally sensitive to hormones in your body but doctors don’t know for sure. While it’s important for your GP to rule out all causes of sinus tachycardia, it might happen for no apparent reason.
If you’re concerned about your heart rate, or have other symptoms, such as chest pain or dizziness, see your GP.
FAQ: What is Wolff–Parkinson–White syndrome?
Wolff–Parkinson–White syndrome is when you have an unusual connection between your atria and your ventricles (the upper and lower chambers of your heart). This can increase your risk of getting supraventricular tachycardia (SVT) and atrial fibrillation.
Wolff–Parkinson–White syndrome happens when the upper and lower chambers of your heart don’t separate properly while you're developing as a baby. This leads to an extra pathway forming between them, called an accessory pathway, which allows electrical impulses to bypass the usual route.
If you have a normal heart, electrical impulses only travel in one direction. This is from your atria to your ventricles, through an area of specialised cells called the atrioventricular (AV) node. If you have Wolff–Parkinson–White syndrome, the accessory pathway allows electrical impulses to arrive at the ventricles quicker than normal. This can speed your heart rate up, and electrical impulses are sometimes transmitted back from the ventricles to the atria, which can cause SVT symptoms. This can be life threatening if you also get atrial fibrillation, but this is rare.
Treatments for Wolff–Parkinson–White syndrome include catheter ablation and antiarrhythmic medicines to help get your heart rhythm back to normal.
FAQ: Can I travel if I have SVT?
Yes, you should be able to travel if you have supraventricular tachycardia (SVT) but it depends on your symptoms.
Most people with SVT can drive and fly but you might be more restricted if you have troublesome symptoms.
If you have SVT, it may affect your ability to control a vehicle so it may not be safe for you to drive. If you don't have any symptoms, you can carry on driving and don't need to notify the Driver and Vehicle Licensing Agency (DVLA). But if you’ve had symptoms, such as feeling dizzy or blacking out, you must stop driving and let the DVLA know. You may be allowed to drive again if your doctor finds a cause of your SVT and you have successful treatment. This will need to have controlled your condition for at least four weeks. The rules for driving with SVT are much stricter if you drive a bus or lorry for work.
Most people with an arrhythmia such as SVT are able to fly safely – flying isn't thought to increase your risk of having an episode. If you have occasional symptoms that are generally well controlled and you don't have many episodes, there aren't any travel restrictions on you flying. If you have more episodes of SVT, you may need to take medicines to make sure you can fly safely. Put the medicines in your hand luggage and ask your doctor to write a letter to declare what they are for. It’s best to contact your airline before you travel to let them know you plan to travel with medicines.
If you're unsure whether or not it's safe for you to travel, ask your GP or heart specialist for advice.
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Reviewed by Rachael Mayfield-Blake, Freelance Health Editor, June 2017
Expert reviewed by Dr Matthew Wright, Consultant Cardiologist and Electrophysiologist
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