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Supraventricular tachycardia (SVT)

Published by Bupa's health information team, June 2008.

This factsheet is for people who have supraventricular tachycardia, or who would like information about it.

Supraventricular tachycardia (or SVT for short) is a type of abnormal heart rhythm (an arrhythmia), which causes the heart to beat very quickly (normally at a rate between 140 and 240 beats a minute).

Animation - The different types of arrhythmia
About supraventricular tachycardia
Symptoms of supraventricular tachycardia
Causes of supraventricular tachycardia
Diagnosis of supraventricular tachycardia
Treatment of supraventricular tachycardia
Further information
Questions and answers
Related topics
Sources

The different types of arrthythmia

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About supraventricular tachycardia

Tachycardia means a rapid heart rate of more than 100 beats per minute. Supraventricular means that the problem starts in the upper part of the heart (above the ventricles).

SVT attacks are often only temporary and frequently go away on their own without medical treatment. They often happen in young, healthy people, with attacks tending to happen less often as you get older.

What happens during supraventricular tachycardia?

Your heartbeat is controlled by electrical impulses, which start in a part of the heart wall called the sinus node, and travel through the heart making it contract. The impulses travel from the atria (the upper chambers of the heart) to the ventricles (the lower chambers) through an area called the atrioventricular (AV) node. The AV node helps to synchronise the pumping action of the atria and ventricles.

Most SVTs happen when there is an extra electrical pathway in the heart, between the atria and the ventricles. This allows electrical impulses to 'short-circuit' and re-enter the atria. The impulses end up travelling around the heart in a circle. These types of SVT are often referred to as re-entrant tachycardias or paroxysmal SVT, which means symptoms can come on suddenly and are temporary.

If the extra pathway is located in your AV node, the SVT is called atrioventricular nodal re-entrant tachycardia (AVNRT).
If the extra pathway is caused by an abnormal connection between your atria and ventricles, the SVT is called atrioventricular re-entrant tachycardia (AVRT).

In AVRT, the abnormal connection between the atria and ventricles can also result in electrical impulses being passed to the ventricles too quickly, as they travel via the alternative route and bypass the AV node. This type of arrhythmia often happens in people who have a condition called Wolff-Parkinson-White syndrome.

Technically, SVT can also include any abnormal heartbeat that starts above the ventricles - including atrial fibrillation - but doctors usually use the term just to refer to the re-entrant tachycardias. A rarer type of SVT is atrial tachycardia, which occurs when the heartbeat is generated by an area of the heart muscle other than the sinus node. It can be associated with some types of heart disease and can also be a side-effect of taking digoxin.

Illustration showing the electrical impulses in a normal heart, a heart with atrioventricular nodal re-entrant tachycardia (AVNRT) and a heart with atrioventricular re-entrant tachycardia (AVRT)
The electrical impulses in a normal heart, a heart with atrioventricular nodal re-entrant tachycardia (AVNRT) and a heart with atrioventricular re-entrant tachycardia (AVRT)

Symptoms of supraventricular tachycardia

Symptoms of SVT can include:

palpitations (you become aware of your heart beating faster or in an irregular way)
shortness of breath
chest pain
dizziness and rarely, fainting

Palpitations are the most common symptom. While symptoms can be unpleasant, they are not normally harmful. Attacks can last from a few seconds to several hours.

These symptoms may be caused by problems other than SVT. You should visit your GP for advice.

Causes of supraventricular tachycardia

The most common type of SVT (AVNRT) most often affects young, healthy people. There is often no reason for an attack and no warning of what is about it happen. However, there are certain trigger factors that may set off an attack. These include:

emotional upset or anxiety
drinking large amounts of coffee or alcohol
smoking a large number of cigarettes

SVT is occasionally associated with an inherited heart condition.

Diagnosis of supraventricular tachycardia

Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history. You may be asked to have an electrocardiogram (ECG) - this is a test that measures the electrical activity in your heart to see how well it is working.

Your GP may refer you to a cardiologist - a doctor specialising in heart conditions - if he or she suspects you have an arrhythmia. A cardiologist may suggest further tests, including:

a 24-hour ECG or a patient-activated recording - this monitors your heart over 24 hours or longer
an implantable loop recorder - this is inserted under your skin so that you can record your heart's electrical activity whenever you have symptoms
an electrophysiological study - this uses electrode catheters to stimulate the heart, allowing doctors to analyse the heart's electrical activity in greater detail than an ECG

Treatment of supraventricular tachycardia

An episode of SVT usually goes away by itself. You may not need to have any specific medical treatment if your palpitations normally stop on their own and don't cause you any trouble.

However, if your symptoms don't improve, are causing you to feel faint, or are making it hard to breathe, you should seek immediate medical attention.

Physical therapies

Your doctor may first try to get rid or your rapid heart beat by using one of the following physical techniques.

Massaging an artery in your neck to stop the rapid heart beat. This must only be done by a doctor. It can be dangerous in some people and your doctor will need to check whether you are suitable for this technique.
The Valsalva manoeuvre. This involves breathing in and then straining out while holding your breath. You may also be taught how to do this technique by yourself - it is easy and safe to perform and is often enough to stop your palpitation.

Your doctor may also advise you on other things you can do yourself to stop an attack, such as immersing your face in cold water, or swallowing something cold, such as a lump of ice cream.

Medicines

If physical techniques don't get rid of your rapid heartbeat, you will probably be given a drug called adenosine to restore your normal heartbeat. This drug is injected into a vein. Sometimes other drugs are given instead of adenosine.

You may also be prescribed medicine over the long-term to help control your heart rhythm.

There are a number of different medicines that can be prescribed to help control heart rhythm and prevent SVT. These include verapamil, diltiazem, beta-blockers and anti-arrhythmic drugs such as amiodarone and flecainide.

Surgery

You may be advised to have a procedure called catheter ablation instead of taking medicine.

In this procedure, the abnormal electrical connections in your heart are identified and destroyed. This is done using small tubes called electrode catheters, which are inserted into one of your veins or arteries, through a small needle puncture in the groin and threaded up to your heart. The catheter emits radio-frequency energy, destroying the nerve fibres that are causing the abnormal rhythm. Another type of catheter may also be used, which destroys the fibres by freezing them (cryotherapy).

The procedure is normally done under a local anaesthetic. This blocks all feeling from the groin, so you will not feel the catheter being inserted but you will stay awake during the procedure and may feel your SVT being set off.

Further information

Arrhythmia Alliance
01789 450787
www.heartrhythmcharity.org.uk
The British Heart Foundation
08450 70 80 70
www.bhf.org.uk