Supraventricular tachycardia (SVT)

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

Animation – The different types of arrhythmia
About SVT
Symptoms of SVT
Complications of SVT
Causes of SVT
Diagnosis of SVT
Treatment of SVT

The different types of arrhythmia

The information on the video provided does not constitute advice on diagnosis or the treatment for heart disease and such advice should always be sought from a doctor or another suitably qualified health professional.

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 your heart (above the ventricles).

SVT episodes are often temporary and frequently go away on their own without any treatment. They often happen in young, healthy people. Episodes often become less frequent as you get older, but you may find they get worse. Episodes vary in how long they last, from a few seconds or minutes, or up to several hours.

What happens during SVT?

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

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

Types of supraventricular tachycardia

There are three main types of SVT, which are described below and in the illustration.

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

Symptoms of SVT

You may or may not have symptoms of SVT. You're more likely to have symptoms if you already have heart disease.

The symptoms you experience during an attack of SVT may include:

• palpitations – you're aware of your heart suddenly beating faster
• shortness of breath
• chest pain
• dizziness and fainting (although this is rare)

These symptoms may be caused by problems other than SVT. If you have any of these symptoms, see a doctor for advice.

Complications of SVT

 
Your heart may not be able to pump blood effectively around your body because your heart rate is abnormal. This can result in low blood pressure, which may cause fainting. Low blood pressure may also result in less blood flowing to your heart (ischaemia), which can damage your heart muscle, causing your heart to pump less effectively. This may result in heart failure. These complications are more common if you have other problems with your heart, such as valve disease.

You also have a small risk of sudden death, but usually only if you have a particular type of SVT called Wolff-Parkinson-White syndrome.
 

Causes of SVT
 

The cause of SVT isn't fully understood at present. Episodes often come on without warning and you may develop SVT without having any underlying cause or risk factor.

However, certain factors may lead to SVT developing, including:

• certain medicines
• problems with your heart since birth (congenital heart disease)
• emotional or physical stress
• hormonal changes
• alcohol
• caffeine
• smoking
• taking illegal drugs, such as cocaine or ecstasy

Diagnosis of SVT

Your doctor will ask about your symptoms and examine you. He or she may check your blood pressure, listen to your heartbeat and take your pulse. You may also have a test called an electrocardiogram (ECG). An ECG records the electrical activity of your heart to see what your heart rhythm is.

If your doctor 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, including:

• blood tests
• echocardiogram – an ultrasound scan of your heart that provides a clear image of your heart muscles and valves, and shows how well your heart is working
• ambulatory ECG – this takes a recording of your heartbeat while you go about your usual 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 over a much longer period
• 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

Please note that availability and use of specific tests may vary from country to country.

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 episode. You can try any of the options below when you feel an SVT episode starting.

• Valsalva manoeuvre. This involves breathing in and then straining out (as if having a bowel movement) while holding your breath – sit or lie down first because this could cause you to faint.
• Diving reflex. Fully immerse your face in cold water or suck on ice cubes.
• Change position. Bend over or lie down.
• Hold your breath or cough.

Your doctor may suggest you improve your heart health by:

• reducing your alcohol and caffeine intake
• stopping smoking, if you smoke
• doing 150 minutes (two and a half hours) of moderate exercise a week in bouts of 10 minutes or more

Physical therapies

Applying pressure to an artery in your neck may help to stop your heart beating rapidly. However, this must only be done by a doctor. It can be dangerous to do on some people and your doctor will need to check whether you're suitable for this technique.

Emergency treatments

Emergency treatments for SVT may include:

• electrical (DC) cardioversion – this uses an electric shock to restore your rapid heartbeat back to normal
• medicines given through a drip into your bloodstream, such as adenosine and verapamil

Medicines

If your symptoms come on suddenly, you may be given anti-arrhythmic medicines, either as tablets or given through a drip into your bloodstream, to try to get your heart rhythm back to normal (this is called pharmacological or medical cardioversion). This is usually tried within 48 hours of having symptoms. If this type of medicine is not successful, you may have DC cardioversion to restore your normal heart rate.

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. You often take them to prevent further SVT attacks.

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

Availability and use of medicines may vary from country to country.

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 if your attacks require regular medication. Small tubes called electrode catheters are passed into the veins in your groin and threaded up to your heart. Any tissue that is disrupting or causing abnormal electrical signals in your heart is burnt or frozen to destroy it.

Availability and use of different treatments may vary from country to country. Ask your doctor for advice on your treatment options.

Produced by Alice Rossiter, Bupa Health Information Team, August 2012.