Supraventricular tachycardia (SVT) is a fast, abnormal heart rhythm that originates from the atria (top chambers of the heart). It is an umbrella term for several different abnormal heart rhythms. Some of these heart rhythms are intermittent, and others are always present. Read on to learn more about SVT, its causes and how we diagnose it. We then discuss SVT treatment in detail so you can make an informed choice about your care.

An SVT is caused generally in 3 ways:

A part or parts of the atria (not the SA node) gives off impulses which can then pass through the heart, overriding the SA node and causing the heart to beat faster (atrial tachycardia)

An extra bit of wiring exists within the AV node allowing a short circuit and fast heart rhythm (AVNRT)

There is an extra bit of wiring present in the heart between the atria and ventricles or within the atria. This can lead to a short circuit, causing a fast heart rhythm (AVRT) or Wolff-Parkinson-White (WPW) syndrome

Even though the heart can beat very fast with an SVT, they are usually not dangerous if the heart is structurally normal. However, certain SVTs occur due to an extra pathway between the top and bottom of the heart. Though it is rare, this may be dangerous.

The ECG could provide clues as to the cause but may also be completely normal. Therefore, your cardiologist might perform a longer heart rhythm trace called a Holter or ambulatory ECG monitor. We attach you to an ECG recorder or patch monitor for a prolonged period – usually 24-48 hours, but it can last up to a week. While you wear the monitor, you go about your day as usual, and it records any symptoms you have. We can then match it to what your heart rhythm was doing at that moment.

Implantable loop recorder

In patients with infrequent episodes, we can implant a small device called an implantable loop recorder under the skin (Reveal LinQ monitor). This device can remain in place for up to 3 years. We implant this in the outpatient setting under local anaesthetic, and the procedure only takes several minutes. Wireless technology means we can stay informed of your heart rhythm without you having to make frequent trips to the hospital.

Additional tests

In addition, we will perform blood tests to ensure there is no other reason for your racing heart. For example, your blood salt and hormone levels can affect your heart’s electrical system. We may also perform an ultrasound scan of the heart (an echo) to see if there are any structural abnormalities and obtain an idea of how well the heart is pumping.

SVT treatment depends on what is causing the SVT and the impact on your life. I.e. how often it happens and how badly it affects you when it does. Some people find that SVT does not affect them very much, and episodes are infrequent. Essentially there are three types of SVT treatment: conservative measures, medications, and catheter ablation.

Conservative measures

These may include holding your breath in a particular way or using cold water. Whilst effective in some patients for stopping the SVT, they may not work. We call these vagal manoeuvres. Visit our blog to learn more about these and other lifestyle changes to help manage an arrhythmia.

Medications

If symptoms are intrusive or frequent, we may offer you medications which can be used on an ‘as required’ basis and taken when the SVT occurs to settle the heart rhythm back to normal. Alternatively, you can use these medications regularly to try and prevent episodes. However, these medications may not be effective for everyone. They can also cause side effects in some. Also, some patients continue to experience episodes despite being on medications. Commonly used drugs include beta-blockers.

Catheter ablation

Nowadays, the first-line treatment for SVT is Catheter Ablation. This SVT treatment is a minimally invasive procedure (not surgery). We pass fine wires from the vein at the top of your leg to the heart. During catheter ablation, we can do a detailed study of your heart’s electrical activity (an EP study) to identify the exact part of the heart that is causing the abnormal electrical activity.

We do this using electrical signals and sometimes a computer-generated virtual map of your heart. During this procedure, we attempt to trigger your SVT in a controlled environment, which helps us make the correct diagnosis. Once we diagnose you with SVT, we deliver high-frequency energy to the tiny area in the heart causing the problem to destroy or modify the abnormal cells. This prevents them from interfering with the electrical pathway of the heart.

Catheter ablation has a success rate of over 90%. We can perform it under local anaesthetic with sedation or a general anaesthetic, usually as a day case. It is a very safe procedure, and the risks of serious complications are low (1-2%). These include bleeding at the top of the leg, bleeding around the heart, and, rarely, a permanent pacemaker.