Supraventricular tachycardia (SVT)

Published by Bupa's Health Information Team, June 2010.

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

Supraventricular tachycardia (SVT) is when the heart beats too fast, usually at a rate of 130 to 250 beats per minute. SVT is a type of arrhythmia (irregular heart rhythm). It is caused by faulty electrical signals in the heart and often affects young healthy people.

The different types of arrhythmia

           A Flash plug-in is required to view this animation.

About SVT

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 treatment. They often happen in young, healthy people, with attacks becoming less frequent as you get older. Attacks can last from a few seconds, minutes to several hours.

What happens during SVT?

Your heartbeat is controlled by electrical signals (impulses), which start in a part of the heart wall called the sinus node, and travel through the heart making it contract. The signals 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.

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

There are three main types of SVT.

• If the extra pathway is located in your AV node - it is called atrioventricular nodal re-entrant tachycardia (AVNRT).
• If the extra pathway is located between your atria and ventricles - it is called atrioventricular re-entrant tachycardia (AVRT).
• If the extra pathway is located in an area other than the sinus node - it is called atrial tachycardia (a less common type of SVT).

Symptoms of SVT

Symptoms of SVT may include:

• palpitations - you're aware of your heart beating faster or in an irregular way
  
• shortness of breath
  
• chest pain
  
• dizziness and rarely, fainting

If you have these symptoms visit your GP, as they may be caused by problems other than SVT.

Complications of SVT

Rarely, a heart attack can occur, especially in people with a particular type of SVT called Wolff-Parkinson-White syndrome.

Causes of SVT

The cause of SVT isn't fully understood at present. Attacks often come on without warning and many people develop SVT without having any underlying cause or risk factor. However, certain factors may trigger SVT:

• alcohol
  
• caffeine
  
• certain medicines
  
• congenital heart disease (problems of the heart since birth)
  
• emotional or physical stress
  
• hormonal changes
  
• smoking
  

Diagnosis of SVT

Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history.

Your GP will check your blood pressure, listen to your heartbeat and take your pulse. You are likely to have a test called an electrocardiogram (ECG). An ECG measures the electrical activity of your heart to see what the heart rhythm is.

If your GP suspects that you have SVT, he or she may refer you to a cardiologist - a doctor specialising in heart conditions. You may have other tests in hospital:

• blood tests
  
• echocardiogram - an ultrasound scan of your heart providing a clear image of your heart muscles and valves and shows how well the heart is working
  
• ambulatory ECG - this takes a recording of your heartbeat while you go about your normal daily activities, over 24 hours or longer
  
• implantable loop recorder - this is placed under your skin so that it can take a recording of your heartbeat
  
• electrophysiological study - this uses electrode catheters to stimulate the heart, allowing your doctor to check your heart's electrical activity in greater detail than an ECG

Treatment of SVT

There are many treatments available for SVT. Your treatment will depend on your symptoms. Your doctor will discuss your treatment options with you.

The aim of treatment is to control your heart rhythm and rate, and reduce your risk of heart failure. You may not need any treatment at all, especially if your symptoms are mild.

Self-help

Your doctor may advise you on things you can do to stop an attack:

• Valsalva manoeuvre - this involves breathing in and then straining out while holding your breath
  
• immersing your face in cold water or sucking ice cubes

Your doctor may suggest you improve your heart health by:

• reducing alcohol and caffeine intake
  
• stopping smoking
  
• doing 150 minutes (two and a half hours) of moderate exercise a week in bouts of 10 minutes or more
  
• eating a balanced diet with five portions of fruit and vegetables every day

Physical therapies

Often people find they can stop SVT by a physical manoeuvre such as bending over, lying down or holding their breath.

Massaging an artery in your neck can help stop a rapid heart beat. However, this must only be done by a doctor. It can be dangerous in some people and your doctor will need to check whether you're suitable for this technique.

Medicines

There are several different types of medicine that can help control your heart rate and rhythm, including beta-blockers, calcium channel blockers and anti-arrhythmic medicines.

Your doctor may prescribe a combination of any of these medicines. You may have to take them for just a short period until you have other treatments such as electrical (DC) cardioversion to restore your heart rhythm, or you may have to take them for months or years. Alternatively, you may be given medicine to take just when you get symptoms.

If your symptoms come on suddenly, you may be given anti-arrhythmics, as tablets or through a vein to try and get your heart rhythm back to normal (this is called chemical or medical cardioversion), and is usually given within 48 hours of having symptoms.

Always ask your doctor for advice and read the patient information leaflet that comes with your medicine.

Electrical (DC) cardioversion

An electric shock is used to restore your heart's normal rhythm. It's usually given if your symptoms have lasted longer than 48 hours and chemical cardioversion has failed. Electrical cardioversion is less likely to work if the arrhythmia has been present for over a year. It's also not suitable if the irregular rhythm is coming and going, since it's most likely that the arrhythmia will return after treatment. For more information see related topics.

Surgery

Surgery is only used when your symptoms haven't responded very well to other treatments. Your doctor may advise you to have a procedure called catheter ablation. Small tubes called electrode catheters are passed into your veins in the groin and threaded up to the heart. Tissue which is disrupting or causing abnormal electrical signals in your heart is burnt or frozen.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.