How Accurate the ECG Is on Your Apple Watch

Apple Watch ECG Accuracy
Qaly Heart
Qaly is built by Stanford engineers and cardiologists, including Dr. Marco Perez, a Stanford Associate Professor of Medicine, Stanford Cardiac Electrophysiologist, and Co-PI of the Apple Heart Study.

Key Takeaways

  • In short, the Apple Watch ECG is very accurate. One study by a Stanford Asociate Professor of Medicine demonstrated that the Apple Watch could accurately detect AFib in 84% of cases when compared to a traditional 12-lead ECG. And in 2020, the FDA cleared the Apple Watch ECG to "serve as a substitute for in-clinic diagnostic testing" during the COVID-19 national emergency in the U.S.
  • While accurate, however, many people report that their Apple Watch ECG tells them they have Afib when they don't.
  • Also, there are also a number of abnormal heart rhythms and irregular heartbeats that the Apple Watch ECG app cannot detect.

Got other questions on your Apple Watch? See the complete set of Qaly guides on Apple Watch:

Introduction

So you have an Apple Watch ECG, or you're thinking about getting one, and now you're wondering "How accurate is the Apple Watch ECG?" Or, you might be thinking, "Is the Apple Watch ECG accuracy high enough to catch abnormal heart rhythms and irregular heartbeats?" In this guide, we'll explore if the Apple Watch ECG is accurate, what its limitations are, and how you might use it to stay heart healthy. Let's dive in.

What's an Electrocardiogram? 

Before diving into accuracy of your Apple Watch's electrocardiogram, or ECG, it's important to understand what exactly it is. (If you're confident in your understanding of an ECG, though, skip on ahead to the next section).

To start, remember how your heart beats? It produces an electrical signal, which squeezes and unsqueezes your heart, which in turn pumps your blood to your lungs for oxygen and then out to the rest of your body.

As that electrical signal flows through your heart, your ECG on your watch sees it, and shows it to you as those awesome-looking waves you know as an ECG. Every time your heart completes one heartbeat, it completes one full cycle of that electrical signal flowing through your heart. And as that electrical signal flows through your heart, it produces different waves on your ECG that capture the squeezing and relaxing of your heart with each heartbeat. If your heart's electrical signal moves irregularly through your heart, it likely means your heart has an abnormal heart rhythm, or arrhythmia. As a result, you'll see an irregular ECG on your watch.

The built-in electrodes in the Apple Watch ECG work with the Apple Watch ECG app to read your heart's electrical signals. If you remember from your physics or electronics course in school, you’ll want to create a circuit for an electrical signal to be able to flow through. By closing the circuit on your Apple Watch with your finger on the Digital Crown, your watch captures the electrical impulses from your heartbeat and translates them into an ECG waveform on your Apple Watch (Series 4, Series 5, Series 6, Series 7, Series 8, or Ultra). Here's how to take an Apple Watch ECG, and how to install the ECG app on your Apple Watch.

A 30-second Apple Watch ECG, in-progress. Through their ECG, this person is recording their heart's electrical signal in real-time. Every time our hearts' electrical signal "fires," it generates a heartbeat. Neat, huh?
A 30-second Apple Watch ECG, in-progress. Through their ECG, this person is recording their heart's electrical signal in real-time. Every time our hearts' electrical signal "fires," it generates a heartbeat. Neat, huh?

So Is the Apple Watch ECG Accurate?

In short, very. One study co-authored and published in the New England Journal of Medicine by Stanford Associate Professor of Medicine and Qaly Co-Founder Dr. Marco Perez, demonstrated that the Apple Watch could accurately detect AFib in 84% of cases when compared to a traditional 12-lead ECG. Moreover, in 2020 during the COVID-19 national emergency in the U.S., the FDA published guidance giving clearance for Apple Watch ECG app to “serve as a substitute for in-clinic diagnostic testing,” so that healthcare providers could “use it for clinical use cases where a single-Lead or Lead I ECG test can help effectively diagnose certain arrhythmias or manage related conditions.”

Here's a Qaly member's Apple Watch ECG. Notice the level of detail that's captured by the Apple Watch ECG on your wrist.
Here's a Qaly member's Apple Watch ECG. Notice the level of detail that's captured by the Apple Watch ECG on your wrist.

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What Are the Limitations of the Apple Watch ECG?

Here are the limitations of the Apple Watch ECG hardware sensor:

Here are the limitations of the Apple Watch ECG software app, that analyzes the Apple Watch ECG sensor data:

  • It does not diagnose, and it should not be relied upon to replace or constitute professional medical care or attention by a qualified healthcare provider.
  • It can show an Inconclusive ECG.
  • It cannot detect Afib under 50 bpm.
  • It cannot detect Afib above 120 bpm on ECG version 1, and above 150 bpm on ECG version 2.
  • It cannot detect arrhythmias other than Afib.
  • It cannot detect heart attacks, blood clots, stroke, or other heart-related conditions.

Here's a Qaly member's Apple Watch ECG showing multiple PVCs. Notice, here, a key limitation of the Apple Watch ECG app: it cannot interpret heart rhythms other than Sinus Rhythm and Afib. It incorrectly labeled this ECG as a Sinus Rhythm ECG, when it should be Sinus Rhythm with PVCs.
Here's a Qaly member's Apple Watch ECG showing multiple PVCs. Notice, here, a key limitation of the Apple Watch ECG app: it cannot interpret heart rhythms other than Sinus Rhythm and Afib. It incorrectly labeled this ECG as a Sinus Rhythm ECG, when it should be Sinus Rhythm with PVCs.

Should I Use the Apple Watch ECG?

The Afib ECG Apple Watch feature is a great tool if you're monitoring your Afib; however, it's hard to understand your ECG for other abnormal heart rhythms and heart palpitations like rapid or skipped heartbeats. Moreover, many people have told the team at Qaly (you can find us on App Store or Play Store) that they experience a high false-positive rate with the Apple Watch ECG atrial fibrillation feature. False-positive means that your watch says you have Afib when you really don't. This can be a really scary and confusing experience for people, causing unnecessary anxiety. With that said, the Apple Watch ECG accuracy, while not perfect, has proven itself to be significantly reliable, and it provides a substantial benefit for people with Afib or at risk of Afib. You may even want to learn how to read an ECG.

As always, if you're experiencing symptoms, discuss them with your healthcare provider as soon as possible to rule out underlying heart conditions.


Conclusion

Well, that just about wraps up our guide on how accurate the ECG is on your Apple Watch. We hope this could be of some help to you.

If you need help interpreting your Apple Watch ECGs, don't worry, we understand how scary and confusing it can be to experience irregular heartbeats. That's why we created the Qaly app for you and for the hundreds of millions of people around the world who live with heart palpitations and abnormal heart rhythms. On the Qaly app, human experts will interpret your Apple Watch ECGs within minutes for clarity and peace of mind.

To get started with the Qaly app for free, grab the Qaly app from the App Store or Play Store today. If you have any more questions, or if you need our help in any other way, don't hesitate to reach out to us at support@qaly.co.

As always from the team at Qaly, stay heart healthy ❤️

Have trouble interpreting your Apple Watch ECG? On the Qaly app, human experts will interpret your Apple Watch ECGs for arrhythmias and irregular heartbeats within minutes. Get started for free today.

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Try Qaly for Free
App Store - Download Qaly | ECG Reader
Try Qaly for Free
Google Play - Download Qaly | ECG Reader
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QALY app - ecg reviews, ecg reader, ecg interpretations, review your ecg

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Have trouble interpreting your Apple Watch ECG? On the Qaly app, human experts will interpret your Apple Watch ECGs for arrhythmias and irregular heartbeats within minutes. Get started for free today.

Try Qaly for Free