What is Apple Watch ECG, how does it work, and how do you set it up?

Apple Watch didn't really focus on health when it first launched in 2014. It was more about fashion, notifications and apps on your wrist - offering a digital alternative to the analogue world that dominated before.

Fast forward six years and the space Apple's smartwatch occupies is vastly different. The Apple Watch Series 6 is very much a health and wellbeing device with a number of features, including an ECG feature and an irregular rhythm notification feature.

Here we explain what the Apple Watch heart features are, how they work, what they mean, and why you might want to use them.

What are the Apple Watch heart features?

• ECG 
• Irregular rhythm notification

The ECG and irregular rhythm notification features were first announced in September 2018, with the ECG feature specific to the Apple Watch Series 4, though it is also available on the Watch Series 5 and the Watch Series 6.

The irregular rhythm notification feature checks heart rhythms in the background every two hours and sends a notification if an irregular heart rhythm is detected. It is available to all Apple Watch users with a Series 1 or later.

The ECG feature meanwhile, is specific to the Apple Watch Series 4, Series 5 and Series 6 and allows users to perform ECG tests from the comfort of their homes rather requiring a local GP or hospital to take a reading.

For those not familiar with the term, an ECG - short for an electrocardiogram - is a way of measuring the timings and strength of electrical signals that make up your heartbeat. By reading an ECG, a doctor can see your heart's rhythm and any irregularities, intervening if required.

How do you get the ECG feature on your Apple Watch?

• Apple Watch Series 4, 5 or 6 required for ECG

The ECG and irregular rhythm notification features are available to Apple Watches running Watch OS 5.2 or later.

As mentioned, the irregular rhythm notification feature is available to other Apple Watch models, from Series 1 and newer, while the ECG feature is unique to the Series 4, Series 5 and Series 6 models.

What do you need to take an ECG with Apple Watch?

• ECG app
• Apple Watch Series 4, 5 or 6
• Supported country

The ECG app is available in the US, Chile, Puerto Rico, Guam, the US Virgin Islands, the UK, New Zealand, and 19 countries within Europe.

Aside from the app, you'll also need the Apple Watch Series 4, Series 5 or Series 6, an iPhone (iPhone 5 or above) and the ability to sit still while you do the test.

How to set up the Apple Watch ECG app

• iOS 12.2 and WatchOS 5.2
• Open Health app

Make sure you are running iOS 12.2 or later and WatchOS 5.2 or later, after which you can access the ECG functionality in the Health app on your phone.

If you're doing this for the first time, you should see a prompt asking you to set it up. If you don't, go to Health Data > Heart > Electrocardiogram (ECG). The setup is incredibly easy and asks for some minimum details, such as age. That's because performing an ECG under the age of 22 isn't recommended. 

Once set up, you can open the Apple Watch ECG app and begin taking an ECG.

How to take an ECG on the Apple Watch

• Open ECG app on Apple Watch Series 4, 5 or 6
• Hold index finger on Digital Crown
• Wait 30 seconds

Once you've set up the app you can take an ECG whenever and wherever you want. The beauty of having the device on you all the time is that you don't have to book an appointment with the doctor.

Simply open the ECG app on the Watch, rest your arm on something to reduce movement, and then hold your index finger (from the arm that doesn't have the watch on it) on the Digital Crown. You don't have to press the Digital Crown. It's all about making a looped connection for the system to monitor what's happening.

The test takes around 30 seconds to complete, and you'll see a representation of your heart rate on the screen while you do it. When complete, the Apple Watch will give you an instant result, along with the ability to record any symptoms you were feeling at the time.

Meanwhile on your iPhone, you'll get a notification with a link straight to the report so you can see further detail or share the results with your doctor.

What do the Apple Watch ECG results mean?

Once you've finished capturing your EGC reading, you'll get one of four messages.

Sinus rhythm means everything is as expected. Atrial fibrillation means there is an irregular pattern detected.

Low or high heart rate is the third potential result, while Inconclusive means the test can't determine the end result.

Can you share your Health information with your doctor?

Of course. To do this, go into the Health App > Browse > Tap Heart > Electrocardiogram (ECG) > ECG result.

You can then export the details via a PDF to share with your doctor. You decide how that information is shared.

Apple doesn't share that information with anyone else like a third-party insurance company, other apps, or even your own computer. 

Is it as good as an ECG in a doctor's office?

Nobody is saying that the Apple Watch ECG is going to be good as or replace a hospital quality electrocardiograph machine, but that's not the idea. A traditional hospital ECG is often referred to as a "12-lead" machine because it uses 10 different electrodes to provide information on 12 different areas of the heart. In contrast, the Apple Watch is akin to a single lead machine.

The documentation refers to the Apple Watch ECG not being a substitute for actual medical care at every opportunity. Support documents from Apple state that the "user is not intended to interpret or take clinical action based on the device output without consultation of a qualified healthcare professional."

And furthermore, "the feature is not intended to replace traditional methods of diagnosis or treatment".

To get the device cleared by the relevant regulatory bodies in the US and Europe, Apple had to provide details of a clinical test of around 600 people, half of whom had atrial fibrillation.

The ECG app was unable to read about 10 per cent of the subjects, but for the others, it was very accurate, according to Apple. The company said "it caught more than 98 percent of people with atrial fibrillation, and correctly told people that they didn't have the condition 99.6 percent of the time."

Apple also carried out another substantial test involving the accuracy of Apple Watch's heart data – the Apple Heart Study with Stanford University, for example, monitored atrial fibrillation, but not the ECG functionality. 

Should Apple give people the ability to do an ECG at home?

Apple has clearly been encouraged by Apple Watch's various successes as a personal medical device. Indeed, it's done a better job at this than any other device before it. The detection of high heart rates has been especially popular and there have been a few cases where the Apple Watch has probably saved lives because it has prompted people to seek medical help.

Ivor Benjamin, president of the American Heart Association was on stage with Apple when the company announced the feature in September 2018.

Benjamin said: "In my experience, people often report symptoms that are absent during their medical visits."

He added: "[This] is game-changing, especially when evaluating atrial fibrillation - an irregular and rapid heart rate that can increase a person's risk of stroke, heart failure and other heart-related complications".

In the UK, Professor Martin Cowie, professor of Cardiology at Imperial College London, based at Royal Brompton Hospital, and chair of the Digital Health Committee of the European Society of Cardiology, has also sung the new ECG feature's capabilities.

"Today, there are around 1.5 million people in the UK living with atrial fibrillation, the most common heart rhythm problem, but a third of these people may be unaware of this. An on-demand ECG and pulse check could be a powerful tool in our ongoing quest to manage heart health better across Europe. The opportunity for innovation to optimise patient care is huge and this is a great step forward."

What is atrial fibrillation?

Atrial fibrillation (or Afib/AF) is where the upper chambers of the heart beat irregularly, increasing the risk of stroke and heart failure.

The irregular rhythm notification feature will check heart rhythms every two hours in the background and send a notification if an irregular heart rhythm is detected.

If an irregular heart rhythm is detected, the Apple Watch will do five further tests in quick succession to see if the outcome is still positive. If it is positive, those using an Apple Watch Series 4, 5 or 6 device will be prompted to do an ECG reading. Those using an Apple Watch Series 1 - 3 and the Watch SE will suggest you contact your local GP. 

Where does Apple Watch ECG work?

Rather than roll out the ECG feature to all Apple Watch users, Apple wants it to only be available in regions "cleared" for a medical device.

Because of that, the ECG feature - which works on Apple Watch Series 4, 5, and 6 and requires iPhone 5s or later on iOS 12.2 or later - isn't available worldwide, though it's getting there quickly. The watchOS 7.6 update (the sixth major update to watchOS 7, which released in September 2020) brought support for the ECG app and irregular heart rhythm notifications to 30 additional regions.

Apple's ECG feature is available in the US, UK, and around 90 other regions and countries globally. You can see the full list of supported areas here.

What can't the heart features do?

The Apple Watch heart features do not detect a heart attack, blood clots, a stroke or other heart-related conditions including high blood pressure, congestive heart failure, high cholesterol or other forms of arrhythmia.

What are the risks?

There are a few caveats, not least that "the ECG app is not intended for use by people under 22 years old [or…] individuals previously diagnosed with AFib". You also need to be still for the ECG to work – "these data are only captured when the user is still."

Equally, "it is not intended to provide a notification on every episode of irregular rhythm suggestive of AFib and the absence of a notification is not intended to indicate no disease process is present". It's a guide, not a 99.9 percent accurate test.

That's key, because some will feel completely assured by the ECG app and not seek appropriate care: "Over-reliance on device output leading to failure to seek treatment despite acute symptoms or discontinuing or modifying treatment for chronic heart condition".

The FDA ruling also points out that "false positive resulting in additional unnecessary medical procedures" could be an issue with the device, resulting in people going for actual ECGs that don't need to happen.

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