Supraventricular tachycardia - Diagnosing supraventricular tachycardia (SVT)

Your GP may suspect you have supraventricular tachycardia (SVT) from a description of your symptoms.

If so, you may be asked to have a test called an electrocardiogram or be referred to a cardiologist (heart specialist).

An electrocardiogram (ECG) is a test that records the rhythm and electrical activity of your heart. It is usually carried out in hospital or in your GP's surgery. It takes about five minutes and is painless

During an ECG, small stickers (electrodes) are stuck to your arms, legs and chest, and connected via wires to an ECG machine. 

Every time your heart beats, it produces tiny electrical signals. An ECG machine traces these signals onto paper. 

Your heart rate during an episode of SVT will usually be between 140 and 250 beats per minute (bpm), compared to a normal heartbeat of 60-100bpm.

If you manage to have the test done during an episode of supraventricular tachycardia, the ECG will record your abnormal heart rate. This confirms SVT and rules out other conditions.

However, it may be difficult to capture an episode, so your doctor may ask you to wear a small, portable electrocardiogram monitor to record your heart rate either continuously over 24 hours, or from when you switch it on at the start of an episode.

Further tests

Further tests may be done once episodes of SVT are confirmed. These are to determine the exact location of the problem in heart.

For example, you may be asked to take part in an electrophysiology study done under sedation, in which doctors pass soft flexible wires up a vein in your leg and into your heart. These wires measure the electrical signals in your heart and enable doctors to locate the problem.