What is supraventricular tachycardia in children? Causes, symptoms and treatment

What is supraventricular tachycardia?

Supraventricular tachycardia (SVT) is a type of fast, regular heartbeat called an arrhythmia that affects the upper chambers of the heart (the atria). Paediatric supraventricular tachycardia is one of the most common heart rhythm disorders in children.

During an episode of supraventricular tachycardia, your heart rate suddenly increases to be much faster than normal. These episodes can last anywhere from a few seconds to minutes to even several hours.

A regular heart rate is usually between 60 and 100 beats per minute. During supraventricular tachycardia, this increases to around 150 to 240 beats per minute.  

What are the common symptoms of supraventricular tachycardia in children?

The most common symptom of supraventricular tachycardia is palpitations, which can cause a pounding or fluttering feeling in the chest, as well as a pounding feeling in the neck and sometimes chest pain.

The rapid heart rate can also cause breathlessness, dizziness and feeling faint. If an episode of SVT occurs during exercise, which is more likely in children, it can even cause fainting. After an episode, SVT can cause feelings of weakness or extreme tiredness.

What causes supraventricular tachycardia?

In children with paediatric supraventricular tachycardia (SVT), the condition is caused by a problem with the heart’s electrical signals that control when it beats. In most cases, it’s caused by an extra electrical connection in the heart that causes a “short circuit”. This “short circuit” results in a sudden increase in heart rate.

There are three main types of SVT, each with a different cause:

• Atrioventricular nodal reentrant tachycardia (AVNRT), where electrical signals controlling how much the ventricles beat get stuck in a circular loop, causing the ventricles to beat much faster.
• Atrioventricular reentrant tachycardia (AVRT), where an extra electrical pathway causes an increase in heart rate.
• Atrial tachycardia, where the atria (upper chambers of the heart) beat faster than the lower chambers due to faulty electrical signals either in a small area (a focus) in the heart, or across a wider area.

Is supraventricular tachycardia in children serious?

In most cases, paediatric supraventricular tachycardia isn’t serious. While the episodes can be disruptive, they usually don’t last long, resolve themselves and don’t pose a wider risk to health.

However, in children, frequent episodes of SVT can stop them from playing sports and enjoying their normal hobbies, and can interfere with their everyday quality of life.

Can supraventricular tachycardia cause a heart attack in children?

In the vast majority of children with SVT, it doesn’t increase their risk of a heart attack. However, some young people have a condition called Wolff-Parkinson-White syndrome. This condition is caused by an extra electrical pathway in the heart that can potentially conduct very rapidly, which can lead to a cardiac arrest. Patients with this condition need to be identified and treated to prevent this.

How is supraventricular tachycardia diagnosed?

We use a combination of signs and tests to diagnose SVT. This includes looking at the patient’s clinical history, performing an electrocardiogram (ECG) to look at the heart’s electrical activity, and arranging a portable ECG monitor to record an ECG during symptoms. An echocardiogram test is also performed, which shows the structure and function of the heart in real time. 

In some cases, patients only experience episodes of SVT during exercise. To detect these, we may perform an exercise echocardiogram or use an implantable loop recorder (ILR). An ILR is a small electronic device that’s implanted just under the skin on the left side of the chest. It records the heart’s electrical activity over a longer period of time, picking up changes that might have been missed with an ECG. If it detects an irregular heart rhythm, it’ll start recording the heart’s activity and send the recording to a cardiologist for assessment. Once the right data has been captured, the ILR can be removed.

How is supraventricular tachycardia treated?

Treatment for paediatric supraventricular tachycardia depends on the frequency and severity of symptoms. The definitive treatment for SVT is catheter ablation, which is effective in 95% of patients in a single procedure. This is a keyhole procedure that involves passing a catheter up through a vein in the top of the leg to the heart. Once it reaches the heart, heat or freezing energy is used to block the electrical conduction in the extra pathway, preventing SVT from occurring.

SVT can also be treated using medication such as daily beta blockers or flecainide. These are helpful in the short term, but become less effective over time and aren’t recommended as a long-term treatment.

If needed, there are also treatments if your child needs acute help during an SVT episode. These include vagal manoeuvres, which are treatments that stimulate your child’s vagus nerve to slow their heart rate. In infants, this can be done by putting ice-cold water on their face for a few seconds to stimulate the diving reflex. In older children, the Valsalva manoeuvre can help stop an acute SVT episode, which involves them breathing out hard against their closed airway, also called ‘bearing down’.