Apple Watch ECG: A guide to using the atrial fibrillation monitor

We explain what it is, how it works and how to use it
Everything to know about Apple Watch ECG
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The headline feature of the latest Apple Watch is electrocardiogram (ECG) heart monitoring, allowing users to take a direct reading from a smartwatch for the first time.


But what exactly is an ECG heart reading, how does Apple perform this from a watch and why is it such a big deal? Well, in this guide we'll be clearing up some of the doubt around the Apple Watch ECG feature and showing you how to use it.

Read next: Complete guide to the Apple Watch heart monitor

Regulatory reasons mean the ECG app still isn't available in every country where the Apple Watch 4 is sold, but we’ve spent plenty of time since launch getting to grips with the feature – read on for everything you need to know.

What is Apple Watch ECG?

In a nutshell, an ECG reading is used to capture the electrical activity in the heart over a short period. Typically, this is performed through a medical-grade ECG machine, though Apple has managed to bring this health technology to its latest smartwatch.

In this specific case, it does so by using both the new electrical heart rate monitor on the underside of the Apple Watch and the Digital Crown, on which users need to place a finger from the opposite hand. This lets the Watch monitor beats across the heart.

The ECG is looking to see if the upper and lower chambers of your heart are in rhythm. If it detects that they're out of rhythm, this is an indicator of the heart condition atrial fibrillation. In a single 30-second test, the Apple Watch can tell you if it think you're showing signs of AFib, but you'll need to perform the test several times to get a stronger indication.

Apple Watch ECG: Getting started

To get started, you must have an Apple Watch Series 4. This is because the ECG feature requires the new Digital Crown to record the electrical pulses, so users with an Apple Watch Series 3, or below, won't be able to use the feature.

You also need to make sure your iPhone and Apple Watch are running the latest version of iOS and watchOS, as this will bring your Health app and ECG app up to date.

Next, open up the Apple Health app on your phone. Assuming you've performed the aforementioned updates, you'll get a prompt to set up the ECG. For this, all you need to do is enter your date of birth, then you'll be asked to take your first ECG reading.


Taking an Apple Watch ECG reading

Apple Watch ECG: A guide to using the new atrial fibrillation monitor

After the initial setup is complete, you can take an ECG reading any time by going into the ECG app on the Apple Watch itself. Before you go any further, you want to make sure the watch is correctly placed on your wrist – not too tight, not too loose – and then, ideally, rest your arm on something. That's what Apple advises, at least, though we've found that as long as you're reasonably still it has no problem getting a read.

Then, touch your index finger from the opposite hand against the Digital Crown. You don't need to do this too hard, just enough that it's covering the entirety of the circle. You'll then see a graphic of your heart rate in real time and a timer counting down from 30 seconds.After 30 seconds, the Watch will be able to give you the results.

Apple Watch ECG: A guide to using the new atrial fibrillation monitor

Sinus rhythm: If everything is good and your heart is beating in a uniform pattern between 50 and 100 BPM, you'll see 'Sinus rhythm' show up. Phew – but we'd still recommend doing it several times and turning on irregular rhythm notifications (we'll get to those in a moment).

Atrial fibrillation: This means the Watch has detected your heart is beating in an irregular pattern within those same heart rate boundaries. If you get this result, you should perform the test several times and consider consulting your doctor.

Low or high heart rate: If your heart rate is higher than 100 BPM or lower than 50 BPM, the reading is deemed inconclusive. There are copious reasons for this; a high heart rate could come from exercise, stress or even alcohol, while a low one can come from intense training. If you do find your heart rate to be too low or high, you should find out why and, if necessary, consult a doctor.

Inconclusive: It's possible for the ECG app to deliver this result, which can arise from many things, including too much movement during the test or having the Watch not fitted correctly on your arm.


Set up irregular rhythm notifications

Apple Watch ECG: A guide to using the new atrial fibrillation monitor

On top of deliberate readings, you can also have the Apple Watch take occasional readings (usually in moments when you're still) to keep an eye for signs of irregular heart patterns. While periodic checks are good, continuous monitoring enables the Apple Watch to receive a more comprehensive picture of how your heart is working. Follow these steps to turn irregular rhythm notifications on:

1. Open the Apple Health app and tap on Health Data.

2. From there, tap on the Heart, scroll down to the bottom and tap on Irregular Rhythm Notifications. You'll need to enter your date of birth again and tell the app whether you've been diagnosed with atrial fibrillation before.

3. The Watch will then monitor for signs of atrial fibrillation, and, if it detects signs on multiple occasions, it'll send you a notification.

Is Apple Watch ECG accurate?

Apple Watch ECG: A guide to using the new atrial fibrillation monitor

Since Tim Cook stood on stage and announced the arrival of the ECG app last September, cardiologists and health experts have speculated on just how accurate the Watch is at detecting irregular rhythms. After all, this kind of thing would usually be reserved for professional equipment handled by, well, medical professionals – not a tech company.

Apple has acknowledged it's got plenty to do before the feature fully reaches its potential, and earlier this year published the results of its related Apple Heart Study, which Stanford University also had a hand in.

The bottom line: It's impossible to know exactly how accurate it is, but it's probably accurate enough.

Why? Well, to get clearance from the FDA in the US and then the CE mark for use in the EEA, it has to meet a certain standard of accuracy. And, during testing of 600 subjects in a controlled environment, the Watch was able to accurately detect the sinus rhythm classification with 99.6% accuracy, and reach the AFib classification with 98.3% accuracy.

The technology isn't flawless, and the Watch can't say for certain if you actually have AFib. Even when it's monitoring throughout the day, it isn't continuous. It also can't detects signs of heart attacks, strokes or other heart conditions. Perhaps the Watch will be able to do these things and more one day, but right now they're not in the smartwatch's purview.

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