Kakapa manawa kakama nā te SVT Fast heartbeat caused by SVT

SVT (also called supraventricular tachycardia) is a disturbance of your heart rhythm. For most people with SVT, it is not dangerous and it will not damage your heart.

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Causes of SVT

People with SVT are usually born with an electrical abnormality of their heart. For a time, the abnormality may cause no problems — the symptoms of SVT may develop in tamariki, rangatahi or adults. 

Some people are born with an extra electrical connection in the heart, creating a condition known as Wolff-Parkinson-White syndrome.

Wolff-Parkinson-White syndrome — Healthdirect Australia (external link)

In some people, an episode of SVT is triggered by exercise, emotional stress, or too much alcohol or caffeine. Or it can happen at any time. Either way, there is usually no warning before it starts.

Symptoms of SVT

A resting heart rate usually is in the range of 60 to 100 beats per minute. It is normal for it to increase to 130 to 150 beats per minute or more when you are physically active.

If you have SVT, there are times when your heart beats much more quickly (often between 150 and 250 times a minute).

Most people with SVT notice their heart racing rapidly for minutes or even hours at a time. An episode will generally start then stop suddenly. While it is happening, you may:

  • feel dizzy
  • be short of breath
  • feel uncomfortable in your chest
  • need to pass wee (urine).

Diagnosing SVT

Your healthcare provider will take a detailed history of your symptoms, which may include:

  • how long they last
  • how often you have them
  • if anything else happens at the same time
  • if there are any triggers, such as exercise
  • if there is a family history of heart problems or sudden early death.

They will check your pulse and blood pressure and listen to your heart.

You will have a tracing of the electrical activity of your heart known as an electrocardiogram (ECG). This will show if you have Wolff- Parkinson-White syndrome.

If you have Wolff-Parkinson-White syndrome, your healthcare provider may recommend more detailed tests to find out if you have a dangerous rhythm problem.

Tests for heart problems (internal link)

Self care for SVT

You may be able to stop an episode of SVT yourself. The best way is to lie down flat and relax for 1 or 2 minutes. If the SVT does not stop, you can try other ways to stop it.

Valsalva manoeuvre

  1. Take a deep breath and hold it.
  2. Keep your mouth closed and pinch your nose shut.
  3. Push your breath out against your closed mouth and nose, as if blowing up a balloon, while straining as if you were doing a poo (bowel motion).
  4. Hold this for 10 to 15 seconds.
  5. Relax and breathe normally.

This is called the Valsalva manoeuvre. Often the SVT will stop 30 seconds or so after relaxing.

Cold water

  • Fill a large bowl with cold water (if possible, put some ice cubes in it).
  • Put your face in the water for as long as you can comfortably hold your breath.

For a tamaiti, you can place a bag of frozen vegetables or a cold, wet facecloth over their face, taking care not to block their breathing.

When to seek urgent medical help for SVT

You should seek urgent medical help if self care does not work or you:

  • have chest pain
  • feel short of breath
  • feel dizzy
  • blackout or lose consciousness.

Treating SVT

If you have a long episode of SVT, you may need a medicine injected into your vein to put your heart back into a normal rhythm.

Very occasionally, you will need cardioversion, which involves a small electric shock to your chest under a brief general anaesthetic.

Medications can be used to prevent SVT. You usually have to take these medicines regularly to prevent the episodes, but some people can take them once the SVT has started.

Your healthcare provider will let you know:

  • which medicine will work best for you
  • how you should take it — depending on what kind of heart rhythm disturbance and other medical conditions you have.

Beta blockers

Beta blockers stop adrenaline from working on your heart and are particularly effective in SVT that is brought on by exercise or emotion. They also lower high blood pressure, treat angina and protect your heart after a heart attack.

Beta blockers can make you tired and cause difficulty sleeping, unusual dreams, depression or impotence. They can also make asthma worse.

Anti-arrhythmic medicines

These medicines can be very effective for many people with SVT. But in some people, they can make it worse. If the medicine makes your SVT worse, you should contact your healthcare provider as soon as possible.

Radiofrequency ablation

Radiofrequency ablation is sometimes used to remove the electrical short circuit that is causing the SVT. This involves a wire being threaded into the heart and heat being used to destroy the abnormal circuit.

Radiofrequency ablation (internal link)

Preventing SVT

Avoid or limit alcohol.

Avoid large amounts of caffeine. Most people with SVT should be able to have a moderate amount of caffeine a day without a problem. A moderate amount is:

  • 5 to 6 cups of tea or instant coffee, or
  • 3 single espresso type coffees, or
  • 4 cups of plunger style coffee.

Manage stress.

If you smoke, you should stop smoking.

Quitting smoking (internal link)