Heart Education
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What First-Degree AV Block Looks Like on Your Watch ECG

QALY Team
First-Degree AV Block caught on an Apple Watch ECG! Interpreted with the QALY 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.

How to Spot First-Degree AV Block on Your Watch ECG

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.

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.

Any 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.

Still Not Sure If It's First-Degree AV Block?

If you're concerned about the ECG tracings from your smartwatch, get them analyzed by experts on the QALY app within minutes. Join others who've gotten peace of mind.

Not Sure If It's First-Degree AV Block? Get Your ECG Analyzed by Experts on the QALY App.

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