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Fast heartbeat caused by SVT

SVT (also called supraventricular tachycardia) is a disturbance of your heart rhythm. Normally, your heart rate depends on how physically active you are, and it beats from 50 to 180 times a minute. If you have SVT, you have periods when your heart beats much more quickly (usually between 150 and 250 times a minute).

What are the symptoms?

SVT faintMost people with SVT will notice their heart racing rapidly for minutes, or even hours, at a time. An episode will generally start, and then stop, suddenly. While it's happening you may feel dizzy and short of breath, and need to pass urine. Your chest may feel uncomfortable. You might not notice the heart symptoms, but feel the other symptoms.

What causes SVT?

People with SVT are usually born with an electrical abnormality of their heart, but otherwise their heart is normal. The SVT may develop during childhood, but might not start until the teenage years, or even adulthood.

In some people an episode of SVT is triggered by exercise or emotional stress. In other people it can happen at any time. In either case, there is usually no warning before it starts.

Is SVT dangerous?

In most people, SVT isn't dangerous and won't damage their heart.

Some people have an abnormality called the Wolff-Parkinson-White syndrome. If you have this, it will show on the ECG (electrocardiogram) that records your heart rhythm. Some people with Wolff-Parkinson-White syndrome can have dangerous heart rhythm disturbances. Your doctor will let you know if there is any risk with your particular hear rhythm disturbance.

What tests do I need?

Most people with SVT need only a physical examination and ECG. If you have Wolff-Parkinson-White syndrome, your doctor may recommend more detailed tests to find out if you have a dangerous rhythm problem.

How can I stop an episode of SVT?

Many people can stop an episode of SVT themselves. The best way is to lie down flat and relax for a minute or two. If the SVT doesn't stop, hold your breath, close your mouth, and bear down – as if you were having a baby or a bowel motion – for 15 to 30 seconds. This is called the Valsalva manoeuvre. You may find that closing your mouth, holding your nose closed and blowing into your nose helps you do this. Then relax and breathe normally. Often the SVT will stop 30 seconds or so after relaxing.

Another way is to fill a large bowl with cold water (if possible, put some ice cubes in it) and put your face in the water for as long as you can comfortably hold your breath. For a small child, place a bag of frozen vegetables over their face, taking care not to block their breathing.

What if it doesn't stop?

If the SVT doesn't stop, or if you're feeling dizzy, or get bad chest pain or shortness of breath, see a doctor immediately. This could be your own GP, an after-hours GP clinic, or the hospital Emergency Department. A medicine that is injected into one of your veins will almost always stop the SVT.

There is a chance you may need a treatment called cardioversion. This is a very safe treatment, that delivers a small electric shock to your chest to correct the heart rhythm disturbance. It is carried out under a brief general anaesthetic.

Can I prevent episodes of SVT?

For some people, cutting down on foods or drinks that stimulate their heart can help. These include caffeine (found in coffee, tea, chocolate, cocoa, cola, and some energy drinks), alcohol, asthma and cold medicines. However, don't stop taking asthma medicines unless your doctor advises you to.

If you are a smoker, you should stop smoking.

There are also many medicines that may prevent episodes of SVT. You usually have to take these medicines regularly to prevent the episodes, but some people can take them once the SVT has started. Your doctor will let you know which medicine will work best for you, and how you should take it, depending on what kind of heart rhythm disturbance and other medical condition you have.

Beta-blockers

Beta-blockers stop adrenaline from working on your heart, and are particularly effective in SVT that is brought on by exercise or emotion. They also lower high blood pressure, treat angina, and protect your heart after a heart attack.

However, they can make you tired, and cause difficulty sleeping, unusual dreams, depression or impotence. They can also make asthma worse.

Anti-arrhythmic medicines

These medicines can be very effective for many people with SVT. However, in some people they can make it worse. If the medicine makes your SVT worse, you should contact your doctor as soon as possible.

Can anything else be done to prevent episodes of SVT?

Most people with SVT are born with an electrical short circuit in their heart. In some people doctors can remove this short circuit with a treatment called radiofrequency ablation.

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Written by Dr Ian Crozier, cardiologist, Canterbury DHB. Adapted by HealthInfo clinical advisers. February 2016.

Image courtesy of CanStock

Page reference: 196534

Review key: HIHPL-25273