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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).

In most people, SVT is not dangerous and will not damage their heart.

Symptoms of SVT

SVT faintMost people with SVT will notice their heart racing rapidly for minutes or even hours at a time. An episode will generally start 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.

Causes of 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.

Some people are born with an extra electrical connection in the heart known as Wolff-Parkinson-White.

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.

Diagnosing SVT

Your doctor will take a detailed history of your symptoms. This is likely to include how long they last, how often you have them, if anything else happens at the same time, if there are any triggers such as exercise and if there is a family history of heart problems or sudden early death.

They will check your pulse and blood pressure and listen to your heart.

You'll have a tracing of the electrical activity of your heart known as an electrocardiogram (ECG). This will show if you have Wolff- Parkinson-White syndrome.

If you have Wolff-Parkinson-White syndrome, your doctor may recommend more detailed tests to find out if you have a dangerous rhythm problem.

Self-care for 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.

If this doesn't work or you have chest pain, feel short of breath, feel dizzy or blackout, seek urgent medical help.

For some people, cutting down on foods or drinks that stimulate their heart can help prevent episodes. These include caffeine (found in coffee, tea, chocolate, cocoa, cola and some energy drinks), alcohol, asthma and cold medicines.

If you smoke, you should stop smoking.

Treating SVT

If you have a long episode of SVT, you may need a medicine injected into your vein to put your heart back into a normal rhythm.

Very occasionally, you'll need cardioversion, which involves a small electric shock to your chest under a brief general anaesthetic.

Medications can be used to prevent 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.

But 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. But in some people, they can make it worse. If the medicine makes your SVT worse, you should contact your doctor as soon as possible.

Radiofrequency ablation

Radiofrequency ablation is occasionally used to remove the electrical short circuit that is causing the SVT. This involves a wire being threaded into the heart and heat being used to destroy the abnormal circuit.

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Written by cardiologist, Canterbury DHB. Adapted by HealthInfo clinical advisers. Last reviewed December 2021.

Image courtesy of CanStock

Page reference: 196534

Review key: HIHPL-25273