Supraventricular tachycardia

Supraventricular tachycardia (SVT) is the name given to an abnormality of heart rhythm, characterised by a fast heartbeat.

You will usually feel your heart suddenly start racing and going very fast, then stop or slow down abruptly. You may also experience:

• chest pain
• dizziness
• light-headedness
• breathlessness

Episodes 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 supraventricular tachycardia.

When to see a doctor

Although SVT is rarely life-threatening, you should contact your GP as soon as possible if you experience symptoms of the condition. A test called an electrocardiogram (ECG) can be used to confirm a diagnosis of the condition 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 the treatment of heart rhythm disorders, called an electrophysiologist.

If you experience severe chest pain or breathing difficulties, or you feel very faint, call 999 for an ambulance.

Read more about diagnosing supraventricular tachycardia.

Why it happens

SVT occurs when there is a problem with the electrical system in the heart that controls your heart rhythm. This causes the heart to beat much faster than normal.

In some people, this is due to a problem with the structure of the heart from birth (Wolff-Parkinson-White syndrome), but it can also occur in hearts that are otherwise normal.

This is why SVT can occur in anyone at any age and why it often occurs for the first time in children or young adults. Generally the fast heart rate occurs more frequently and lasts longer the older you get.

SVT is can be triggered by the extra heartbeats called ectopic heartbeats that most people experience, but some episodes are brought on by things like drinking large amount of alcohol or caffeine, stress, or smoking lots of cigarettes.

Read more about the causes of supraventricular tachycardia.

Treating SVT

Most episodes of SVT are harmless, do not last long and settle on their own without treatment. However, treatments are available to stop ongoing episodes and prevent them occurring in the future if necessary.

Ongoing episodes of SVT can sometimes be stopped using manoeuvres that help slow down the electrical impulses in the heart by stimulating a nerve called the vagus nerve, such as the Valsalva manoeuvre. This manoeuvre usually involves holding your nose, closing your mouth and trying to exhale hard while straining as if you were on the toilet, or giving birth.

If manoeuvres like this are ineffective, injections of medication or an electric shock treatment called cardioversion can usually help stop ongoing SVT episodes.

In order to prevent future episodes, medication can be prescribed to be taken every day or a procedure called catheter ablation may be used. This procedure involves destroying the tiny areas of the heart causing problems and it is very effective at preventing future episodes.

Read more about treating supraventricular tachycardia.