What Supraventricular Tachycardia (SVT) Looks Like on Your Watch ECG

Supraventricular Tachycardia (SVT) captured on a smartwatch (Apple Watch, Samsung Watch, Fitbit) ECG.

Key Takeaways

Supraventricular tachycardia (SVT) is a fast rhythm originating in the heart's upper chambers (atrium). Usually, your heart rate is between 60 and 100 beats per minute. However, SVTs are significantly faster, occurring between 150 and 220 beats per minute.

How to Spot SVT on Your Watch ECG

So how can you tell whether you have supraventricular tachycardia? Look for the following characteristics in your smartwatch ECG:

  • The rhythm is regular, and the heart rate is greater than 150 beats per minute.
  • P waves are often hidden. They are partially or completely buried within or at the end of the preceding T wave.
  • The QRS complex will usually be narrow, less than 120 milliseconds. It is occasionally widened if there is a co-existing bundle branch block. 

Non-sustained SVT lasts less than 30 seconds, whereas sustained SVT lasts longer, sometimes even up to several hours.

And while SVT is a faster-than-normal heartbeat, known as tachycardia, it isn't the same as Sinus Tachycardia. Know the difference in SVT vs Sinus Tach.

Example of an Apple Watch ECG showing sustained SVT. The rhythm is regular with the heart rate greater than 150, P-waves are not visible, the QRS interval is narrow (< 120 milliseconds), and the SVT is sustained for 30 seconds.

Example of an Apple Watch ECG showing non-sustained SVT. The heart rate is very fast for the first 9 seconds, where the P waves are partially visible, indicating SVT. The SVT then transitions to the underlying rhythm of sinus tachycardia. Since the SVT lasts for less than 30 seconds, this is considered non-sustained SVT. 

Smartwatches like the Apple Watch and Samsung Watch capture a 30-second 1-lead ECG of your heart. These smartwatch ECGs can capture initial evidence that you may have SVT. While they can't provide a complete perspective of the heart like a 12-lead ECG you'd get in a doctor's office, they can alert you when your heart is beating abnormally fast. If a cardiac technician on the QALY app identifies an SVT on your smartwatch ECG, contact your doctor for a complete cardiac investigation to diagnose the problem.

What Causes SVT?

Since the term “supraventricular tachycardia” refers to several different types of fast heartbeats, there are different causes.  

Atrial tachycardia: They are short runs of SVT and are typically caused by one or more areas in the top part of the heart (atria) that have started to beat automatically and faster than the normal heartbeat. This is sometimes seen when the top part of the heart stretches or scars with age or other conditions affecting the heart muscle.

Re-entry tachycardia: They are caused by the presence of an extra electrical connection that can then result in an electrical loop. The electrical connection is something that a small percentage of people are born with. However, it may not cause fast heartbeats until later in life.

What are Common Symptoms and Treatment Options?

Some people don't get any symptoms at all. However, it's prevalent to feel your heart racing or have palpitations. In addition, people with SVT may feel dizzy, be short of breath, or have chest pain. SVT and its associated symptoms can last a few minutes or several hours.

Although some SVTs resolve naturally, others require treatment. Most need further evaluation to make an accurate diagnosis, such as a 12-lead ECG, a 48-hour monitor, or electrophysiological studies and mapping. Again, your smartwatch can be helpful because it enables you to record symptoms and what you were doing when the SVT started.

Treatments typically include slowing the heart rate using a drug called adenosine. Another option is cardioversion done with a defibrillator synchronized to discharge at a specific stage in a heartbeat. Some people need medication to keep the arrhythmia under control. In other cases, ablation of a re-entry pathway is done to stop arrhythmias.

Treatment varies depending on your specific condition. Once your doctor has an accurate diagnosis, they can advise you on the best course of treatment for your SVT.

Any Cause for Concern?

SVTs are rapid heart rates that can cause people to feel unwell. If you have chest pain or sudden shortness of breath, along with an SVT, you should call 911.

You must be checked out immediately for several reasons when you develop a rapid heart rate like SVT. First, the strain on the heart caused by the additional pressure and rapid heartbeat can lead to collapse or heart damage. Second, those with many episodes of non-sustained SVT may be at risk of having atrial fibrillation in the future. Finally, if SVT is left untreated, it can lead to a stroke. This happens due to the ineffective blood pumping in the circulatory system, causing the blood to thicken and form clots.

The underlying cause of SVT needs to be investigated and the arrhythmia treated. For example, some SVTs are caused by thyroid disease, overuse of some medications, and underlying heart problems. Excess caffeine and recreational drug use also lead to SVT. In addition, some people have re-entry tachycardia that must be examined to ensure the correct treatment is given. 

Finally, SVT can sometimes be confused with VTach. Know the difference in SVT vs Vtach.

Staying Healthy with a Smartwatch

If you have SVT, you'll need to make lifestyle changes, such as quitting smoking and avoiding too much caffeine. A smartwatch can help you stay healthy by assisting with weight management and the amount of exercise you do to help keep your heart in good shape. In addition, you can use it to ensure you relax and sleep well, enabling your heart and body to get the rest it needs.

If you want to understand more about heart ECG traces on your smartwatch, contact QALY (Android or iOS) to get an explanation within minutes.

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