Heart Education
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First-degree AV block – can your watch ECG detect it?

ReadMyECG Team
First-Degree AV Block caught with a smartwatch (Apple Watch, Fitbit, Samsung) and interpreted with the ReadMyECG app.

Key Takeaways

First-degree atrioventricular (AV) block is seen when there is a delay between the contraction of the top chamber of the heart (atrium) and the bottom chamber of the heart (ventricle). It usually indicates a problem with the conduction system in your heart.

Example of PR interval in ECG
In a first-degree AV block, the PR interval is greater than 200 milliseconds.

A heartbeat starts in the heart's right atrium and passes through the AV node to the ventricles. In a first-degree heart block, there is a delay in the heartbeat traveling through the AV node

On an ECG, the distance between the small P wave representing atrial contraction and the more significant QRS wave, known as the PR interval, is longer than usual and greater than 200 milliseconds.

First Degree AV Block cought with Apple Watch interpret with ReadMyECG app
Apple Watch ECG with a prolonged PR interval of 220 milliseconds, indicating a first-degree atrioventricular (AV) block.

Common Symptoms of First-Degree AV Block

Most people don't realize they have a problem with first-degree AV heart block until they see a heart tracing or are being tested for an unrelated medical condition. However, others experience symptoms such as lightheadedness or feeling dizzy due to the prolonged delay in the heartbeat forming as it then interferes with normal blood flow.

What Causes First-Degree AV Block?

Several different things cause first-degree heart block. Some people, especially if they have an existing heart defect, are born with it. However, it is more common for first-degree AV block to develop later in life. For example, it sometimes develops if you have an existing heart condition such as angina or have had a heart attack. It is also common after heart surgery.

First-degree heart block can also occur if you are on medications such as digoxin, which slows the heart rate but can sometimes lead to heart block. Sometimes, other medical conditions like Lyme disease can cause first-degree AV block.

What Is a Cause for Concern?

Most people don't realize they have first-degree AV block because they don't have any symptoms. However, if the arrhythmia appears on your heart tracing, the first thing to consider is whether you feel unwell. If you also have chest pain, sudden shortness of breath, or dizziness, call your doctor or ring 911. If you feel fine but are taking medication, it is worth speaking to your doctor because the dosage may need to be adjusted. In addition, your doctor will want to monitor your heart rhythm closely to see whether the problem has been resolved. Sometimes, first-degree heart block can develop into a more severe variety of AV block or another arrhythmia, which will require treatment from a cardiologist, so it does need to be watched closely.

Can Your Smartwatch Detect It?

Smartwatches like the Samsung Watch and Apple Watch have several features that you will find helpful. They monitor how much exercise you do and the calories you burn up. Many smartwatch designs also feature an ECG recorder. They are simple to set up and record your heart rhythm at rest and during exercise. Currently, there are no smartwatches that automatically identify a first-degree AV block.

In the case of first-degree AV block, you can monitor the PR interval on your ECG and see if it is greater than 200 milliseconds. You can also note any symptoms you are experiencing when you take your ECG. If you are unsure about the tracing or want some advice, you can submit your ECG to the ReadMyECG app (Android or iOS), where an expert can check your smartwatch tracing and advise you on what to do next. Most of the time, there's no problem. 

How To Stay Healthy

If you have a smartwatch, it is an excellent opportunity to use apps to stay healthy and prevent the development of conditions such as heart disease and diabetes. Use the watch to control your exercise levels, sleep patterns, and eating habits.

Finally, if you are concerned about the ECG tracings from your smartwatch, you can get them reviewed by experts for arrhythmias within minutes. It will give you peace of mind and help you get an assessment if needed. Reach out to us (Android or iOS) for a review or if you have any questions.

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