Supraventricular tachycardia (SVT): treatment, symptoms, causes and when to get help

The NHS says if your episodes last only a few minutes and do not bother you, you may not need treatment. Cutting down on caffeine and alcohol and stopping or cutting back on smoking may reduce the chance of episodes, and your doctor may recommend simple techniques to help stop episodes when they happen.

Great Ormond Street Hospital describes these as vagal manoeuvres, which work on the vagus nerve that regulates the heartbeat, and gives blowing through a straw or into a balloon as examples taught to children. Ask a clinician which technique is suitable for you and have it demonstrated; do not press on your neck or eyes.

If you keep having long episodes, the NHS says you may need treatment in hospital: medicines to control the episodes, given as tablets or through a vein; cardioversion, a small electric shock to help the heart get back to a normal rhythm; or catheter ablation, where thin tubes are placed through a vein or artery into the heart and heat or freezing is used to correct the electrical problem, which permanently cures the problem in most people.

Great Ormond Street adds that for people whose symptoms affect daily life medication such as a beta blocker can be offered, and that cardiac ablation is the most effective long-term treatment. It says radiofrequency (heating) ablation is effective in around 90 per cent or more of cases and cryoablation (freezing) in about 80 per cent, and is carried out at low risk as a day case or with an overnight stay.

The NHS explains that SVT happens when the electrical system that controls your heart rhythm is not working properly, so the heart suddenly beats much faster, then can slow down abruptly. It can happen when resting or exercising.

Great Ormond Street describes SVT as often caused by an additional electrical pathway, or a short circuit near the AV node, that forms as the heart develops before birth and may become active at birth or later in life. The extra pathway lets the signal loop round and round, producing a regular but very fast heart rate, often around 200 beats per minute.

The NHS says SVT causes the heart to suddenly beat faster, and you may get no other symptoms, but sometimes people also have chest pain or discomfort, feel weak, breathless, lightheaded or dizzy, or feel tired. Great Ormond Street says fainting is rare and usually only occurs after more than 30 minutes of heart racing.

In babies and young children who cannot describe palpitations, Great Ormond Street says they may seem breathless, pale, irritable or unsettled, and you may be able to feel the heart racing by placing a hand on the chest.

The NHS says SVT happens when the electrical system controlling the heart rhythm is not working properly. Episodes can be triggered by caffeine, alcohol or drugs, but often there is no obvious trigger. It can happen at any age, though it often starts for the first time in children and young adults and many people have their first symptoms between 25 and 40.

Great Ormond Street says the underlying cause is often an extra electrical pathway or short circuit that forms when the heart is developing. This is why SVT can first appear later in life even though the wiring has been there since birth.

The NHS says some people get heart palpitations during pregnancy, and the British Heart Foundation lists hormonal changes due to pregnancy among other causes of palpitations. The sources read for this guide do not give specific figures or treatment rules for SVT in pregnancy, so decisions need to be made with your team.

If you have SVT and are pregnant or planning pregnancy, tell your midwife and GP so that your care can be coordinated with cardiology or obstetric medicine. Seek urgent help (999) if a fast heartbeat comes with chest pain, shortness of breath or feeling faint, as for anyone else.

The NHS says see a GP if you keep getting a fast heartbeat, as you might need a test such as an electrocardiogram (ECG). Great Ormond Street says SVT is usually diagnosed on an ECG at the time of symptoms, and sometimes by accident on an ECG as part of a general check-up.

Because episodes often stop before you reach a clinic, it describes an exercise test to bring on an episode, an ECG worn over 24 hours or longer, or an implantable loop recorder, together with an echocardiogram to look at blood flow through the heart. A history, including family history, is also taken.

The NHS says to call 999 if you have been diagnosed with SVT and your episode has lasted longer than usual, or if you have a fast heartbeat with shortness of breath, chest pain or feeling faint. You need to go to hospital for treatment immediately. Do not drive yourself to A&E.

For children, Great Ormond Street lists red flags as changes in behaviour, lethargy or irritation, dizziness or feeling faint, collapse, colour changes such as dusky or pale skin, clamminess or cool hands and feet, and breathlessness. If a prolonged episode reaches hospital, simple manoeuvres are tried first, then medication, and as a last resort a shock.

The NHS heart palpitations page says to call 999 if palpitations do not go away or come with chest pain, shortness of breath or fainting, and to ask for an urgent GP appointment or call 111 if they have stopped but you had these symptoms.

Most people are first seen by a GP, who arranges an ECG and may refer on to cardiology and, if ablation is considered, to a cardiac electrophysiologist. Waiting times for non-urgent heart rhythm procedures vary between NHS trusts.

Private cardiology offers monitoring and consultations, and some centres perform ablation. If you are considering this, ask which rhythm you have, which type of ablation is proposed, what the operator's own success and complication information is and how follow-up is arranged.