Supraventricular tachycardia (SVT)
Supraventricular tachycardia, or SVT, means episodes of a very fast heartbeat that start and stop abruptly, as though someone had flicked a switch.
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Medicines commonly prescribed for Supraventricular tachycardia (SVT)
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: MODIFIED-RELEASE CAPSULE, 240 mgActive substance: diltiazemManufacturer: Lacer S.A.Prescription requiredDosage form: TABLET, 100 mgActive substance: metoprololManufacturer: Aurovitas Spain, S.A.U.Prescription requiredDosage form: MODIFIED-RELEASE CAPSULE, 180 mgActive substance: diltiazemManufacturer: Viatris Healthcare LimitedPrescription required
Supraventricular tachycardia, or SVT, means episodes of a very fast heartbeat that start and stop abruptly, as though someone had flicked a switch. One moment everything is ordinary, the next the heart is racing at a speed that neither exertion nor nerves can explain. It is frightening, but it is almost never life-threatening. And unlike many heart conditions, it is not just manageable: in most people it can be got rid of altogether, which is something a great many people with SVT are never told.
What an episode feels like
An episode of SVT is recognised not by how hard the heart beats, but by the shape of it.
- An abrupt start and an equally abrupt finish. There is a single beat between "I feel fine" and "my heart is pounding". It ends the same way: people often describe a thump or a lurch inside the chest, after which everything falls quiet.
- A steady, very fast rhythm. The heart beats quickly but regularly, with no stumbles or pauses, like a metronome set far too fast. That is what separates SVT from atrial fibrillation, where the rhythm is ragged and uneven.
- Pounding in the neck. Many people feel a thudding near the throat, and sometimes the neck veins can be seen pulsing. It is a characteristic sign and worth mentioning to your doctor.
- Weakness, breathlessness, mild dizziness, anxiety, a sense of not getting enough air. It is common to need the toilet just after an episode ends: that is part of the picture, not a coincidence.
An episode usually lasts from a few minutes to an hour or two, occasionally longer. It may come once every few years or several times a week, and there is no way to predict it. The first one often arrives in young adulthood, but plenty of people have their first episode at forty or at sixty.
What happens inside the heart, and what makes episodes likelier
The rhythm is set by the heart's own electrical system: the impulse begins in the atrium and travels along a strictly defined route to the ventricles. In SVT there is an extra patch of tissue or an additional conducting pathway in the upper part of the heart, and the impulse can travel round it in a loop. One early beat entering that loop is enough for the excitation to start circling on its own, imposing its own fast pace on the heart. When the loop breaks, the episode stops instantly. Hence the abruptness at both ends.
This is not a worn-out heart, and it is not the price of an unhealthy life. The quirk in the conducting pathways is usually present from birth; it simply had not shown itself until now. The heart itself is generally healthy, and a scan shows nothing wrong with its structure.
Some circumstances make episodes more likely: too little sleep, strong coffee and energy drinks, alcohol, stress, dehydration, a high temperature, an overactive thyroid, stimulants and some decongestant cold remedies. Some people can always name a trigger and others never can, and both are ordinary.
Manoeuvres that may stop an episode
An episode can sometimes be stopped without medicines. These techniques work through the vagus nerve, which slows conduction inside the heart, and are known as vagal manoeuvres. They do not always succeed, but they are worth trying.
- Bearing down. Take a breath, hold it and strain hard, as if opening your bowels, for about fifteen seconds, then relax. It works noticeably better if you lie flat immediately afterwards and someone raises your legs.
- Blowing against a closed mouth. Pinch your nose, keep your mouth shut and try to blow out hard: no air escapes and the pressure inside the chest rises.
- Cold on the face. Splash your face with very cold water, hold an ice pack wrapped in a towel against it, or dip your face into cold water for a few seconds.
Two conditions, without which this advice is of little use. First, the manoeuvres should be demonstrated by a doctor, who will also confirm that your episodes are the kind that respond to them and explain how many attempts to make and for how long. Second, never massage your own neck. Pressure on the carotid artery is genuinely used, but only by a doctor and only where there are the means to act if the rhythm slows too much; in older people and in anyone with narrowed arteries it is dangerous. Do the manoeuvres sitting or lying down, never while driving, in the bath or in water. If two or three attempts fail, stop trying and get help.
When to call an ambulance
A short episode that settled on its own is a reason to book an appointment calmly. But some situations cannot wait.
Call an ambulance (112 works as a single emergency number across Europe) if, along with the fast heartbeat, there is:
- pain, pressure or tightness in the chest;
- severe breathlessness, or being unable to speak in full sentences;
- fainting or the feeling of being about to faint: vision darkening, the room swimming, legs giving way;
- sudden pallor, cold sweat, confusion;
- an episode that will not stop: longer than your own usual episodes, or beyond half an hour, with vagal manoeuvres having failed.
Nobody should drive in that state, neither to hospital alone nor carrying the person having the episode. If a heartbeat like this happens for the very first time and you do not understand what is going on, call as well: capturing the rhythm while it is present matters.
Why capturing an episode on an ECG matters so much
This is the central difficulty of the whole subject: between episodes the ECG is usually entirely normal. Someone comes in two days after an episode, a tracing is taken, it looks clean, and the conversation ends with "there is nothing wrong with you". No diagnosis has been made, because what needs catching is not the resting heart but the episode itself.
So the investigation is built around a single aim: getting a recording of the rhythm while the heart is racing.
- an ECG taken during an episode is the most valuable thing there is; if it happens somewhere with medical care available, ask for a tracing there and then rather than waiting for it to pass;
- continuous monitoring over 24 hours or several days, when episodes are frequent;
- an event recorder, worn for weeks and switched on as the episode starts, which is the only realistic option when episodes are rare;
- traces from personal devices with an ECG function: they do not replace a proper assessment, but they can show your doctor the shape of the rhythm;
- thyroid blood tests and a heart scan, to see whether anything else is contributing.
Until there is a diagnosis, a short diary helps: date, time, how long it lasted, what you were doing, how it ended. That note tells a doctor more than you would expect.
What treatment involves
If episodes are infrequent, brief and easily tolerated, no treatment may be needed at all: it is enough to know how to stop them and to remove the obvious triggers.
When they get in the way of daily life, medicines come in. Some are given into a vein in hospital to break a prolonged episode; they work within seconds, and a brief unpleasant sensation in the chest is expected. Others are taken as tablets, regularly or as required, to make episodes less frequent: usually beta blockers or calcium channel blockers. A doctor chooses them, and that is not a formality: a drug that helps one rhythm disturbance can be dangerous in another, so taking "something for the heart" on a friend's recommendation is not acceptable with an arrhythmia. If nothing stops the episode and the person is unwell with it, hospital treatment includes cardioversion, a brief shock given under sedation that restores the normal rhythm.
Driving, heavy lifting and planning a pregnancy are worth a separate conversation. Usually there are no restrictions, or only temporary ones, but the answer depends on how your own episodes behave.
Ablation: the episodes can be gone for good
This is the part worth reading to the end for. With SVT there is not only a way of quelling episodes, but a way of removing what causes them.
Catheter ablation is done without any incision: fine catheters are passed to the heart through a vein in the groin, the extra conducting pathway is located, and it is destroyed at that precise spot with heat or with cold. It usually takes a few hours, and people go home the same day or the next. For most forms of SVT the procedure settles the cause permanently: no more episodes, and no maintenance tablets.
Like any procedure it carries risks; they are small, and they are discussed in detail beforehand, together with which form of SVT you have been found to have, since that also determines the chance of success. The point is this: if your episodes are frequent, long, or simply poison daily life with waiting for the next one, it is entirely reasonable to raise ablation yourself rather than waiting to be offered it. Many people live with episodes for years believing there is no choice, and there is one.
Online consultation
An episode in progress is not something to sort out remotely: if it is severe or will not stop, an ambulance is needed. Everything around the episode, though, is well suited to a remote appointment. The doctor will go through exactly how your fast heartbeat begins and ends, and that description alone often shows whether SVT is likely or something else is going on, and which test will catch the rhythm. They will help you plan that recording: what to ask for if an episode catches you in a clinic, and which type of monitor to discuss with a cardiologist. They will explain and demonstrate vagal manoeuvres if those suit you. They will go through tracings and reports you already have and say what the form of SVT found actually means. And they will talk through ablation: who is offered it, what to expect from it, and which questions to take to the arrhythmia specialist in person.
This material is for information only and does not replace medical advice.
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