Atrial Fibrillation: A Guide to Wearable ECG Smart Watches (2024)

AFib occurs when there are abnormal electrical impulses in the heart. During an episode, there is chaotic electrical activity in the atria (the top chambers of the heart), rather than normal, highly regulated signals. These signals cause the muscle fibres in the atria to contract out of time with each other, and the atria ‘quiver’ (or ‘fibrillate’). 

The heart normally requires coordinated waves of activity to pass from the atria to the ventricles (the bottom chambers of the heart), which are the heart’s main pump and create the heart beat that you might feel. In AFib, the chaotic activity from the atria no longer sends rhythmic signals to the ventricles – the activity instead can be rapid, or slow or just randomly irregular. As a result, the person’s heart beat during AFib can be rapid, slow or irregular.

An ECG is a recording of the electrical activity of the heart, and is an extremely important diagnostic and monitoring tool for patients with AFib. They are also used to help diagnose a range of other cardiac conditions. An ECG is a painless, non-invasive way to measure the electrical signals of the heart.

A traditional ECG test performed in a clinic or hospital uses 12 electrodes placed on different parts of the body to measure the electrical activity of the heart from multiple perspectives. The electrodes are usually small adhesive stickers attached on the skin. The ECG recording is shown as a series of waves of heart rhythm intervals that are viewed and interpreted by a cardiologist. The 12-lead ECG is considered to be the ‘gold standard’ for ECG testing and is typically used in a clinical setting.

The cardiologist looks at the shape of the waveform and each of its components, how frequently they occur, whether the spaces between are even or variable. The Cardiac Electrophysiologists (or Cardiologists who have specialised in Heart Rhythms) are able to use this information to diagnose a wide range of conditions from an ECG. Twelve lead ECGs also enable Electrophysiologists to diagnose the location of a problem within the heart.

With the launch of new wearable technology, electrodes within smart watches can enable wearers to take an ECG themselves – directly from their wrist, via their watch, and view their results in real-time.

In addition to taking the ECG, smart devices also use computed algorithms to detect specific types of arrhythmias, particularly AFib. They are now increasingly able to alert the wearer – some people may now first be alerted to signs of AFib by their watch!

There are several limitations in taking an ECG from a wearable device, compared to a 12-Lead ECG.

• Limited information: Because a wearable device is a single-lead ECG, it provides less information about the heart’s electrical activity than a 12-lead ECG. This means that certain heart conditions may not be detectable with a smartwatch ECG.
• Limited accuracy: Smartwatch ECGs use a single electrode sensor, which may not provide as accurate measurements as the multiple electrodes used in a 12-lead ECG. This means that the results of a smartwatch ECG may not be as reliable as those from a traditional ECG.

• Limitations in detecting cardiac conditions: Single-lead ECGs typically cannot detect certain cardiac conditions, such as a bundle branch block or a left ventricular hypertrophy.
• Interference: The signal detected by the single-lead ECG is prone to noise, interference and artifact which can affect the quality of the ECG tracing.
• Dependence on correct positioning of the device: Smartwatch ECGs require the user to wear the device in the correct position to ensure accurate measurements.
• Not intended for diagnosis: The smartwatch ECG is not intended to diagnose, cure, mitigate, treat, or prevent any disease or medical condition and should not be used as a substitute for a traditional ECG or medical advice.

The accuracy of the algorithm that detects atrial fibrillation (AFib) in a smartwatch device can vary depending on the device and the algorithm used.

In general, studies have shown that the sensitivity and specificity of smartwatch algorithms for detecting AFib ranges from about 70-90%. Sensitivity refers to the ability of the algorithm to correctly identify cases of AFib, while specificity refers to the ability of the algorithm to correctly identify cases where AFib is not present.

However, the accuracy of smartwatch algorithms for detecting AFib can be influenced by several factors, including:

• The quality of the ECG signal: Smartwatch ECGs are typically less accurate than traditional 12-lead ECGs, and the accuracy of the algorithm may be affected by noise, interference, and artifacts in the ECG signal.
• User factors: The accuracy of the algorithm may be affected by the user’s physiology, posture, and other factors such as skin conditions, medications and the device itself.
• Heart rate: Some algorithms specify that their ability to detect AFib is reduced at high heart rates
• Limitations in the algorithm: The algorithm’s ability to detect AFib may be limited by its design and the data it is trained on.

Overall, smartwatch algorithms are more likely to be more accurate in detecting more obvious cases of Atrial Fibrillation, whereas more subtle cases may be more challenging to detect.

It is important to note that while the quality of the single lead ECG from a wearable device has been endorsed as ‘medical grade’ accuracy, the algorithms that interpret that ECG may not have as high a level of accuracy.

One of the main benefits of wearable ECGs for people with AFib is that you can be empowered to capture your own heart rhythm when you feel your symptoms and then can share this critical information about your health with their doctors.

Dr Robert Perel, Cardiac Electrophysiologist, Cardiologist and Director of Queensland Cardiovascular Group, explains how smart devices are changing the way heart rhythm conditions are detected and diagnosed.

“Until about five years ago people couldn’t record their own ECG at home. Traditionally people used to come to a cardiologist due to symptoms like palpitations, with a general idea of when they occurred. We would then arrange for monitoring study done (for example, a Holter study), and hope that we can catch that same rhythm if it occurred again during the period that they are wearing the monitor,” he said.

Dr Perel said that in some cases, people have gone for years without a diagnosis – they know they’ve got a symptom, but no one can ever capture it at the right time, particularly as AFib can ‘come and go’. However wearable tech that can take spot readings at any time, gives patients the power to find the ‘missing pieces of information’.

“Now patients can visit their cardiologist and say “this is what I felt, and here is what the ECG from my watch showed at the time that I felt it. This means that together we can look at your rhythm and correlate it with your symptoms. And that’s so much more efficient to get to an AFib diagnosis, and then begin management,” Dr Perel said.

It is important to remember that while wearable devices can help detect AFib, it is a complex condition, and it is needs to be investigated thoroughly and diagnosedby a doctor.Dr Perel said that although wearable devices can have a medical grade ECG recording, and reasonably accurate automated identification of AFib, it’s important to work with your doctor for a diagnosis. A Cardiac Electrophysiologist may want to look at the ECGs from your device recorded while your symptoms are present to interpret information beyond the capacity of the current algorithms. They may also need to follow up with a 12-lead ECG and other tests for further information to inform your diagnosis and treatment options.

According to Dr Perel, he has found that many of his patients with AFib find a wearable ECG device to be useful.

“I tend to have two groups of patients who benefit the most using their smart devices. One group tends to use it to monitor their heart rhythm symptoms and confirm if they are in Atrial Fibrillation (or a different rhythm).”

The other group who I find benefit highly from their smart devices are those that use it to monitor and improve their cardiac and general health. I find that some patients benefit from using apps that help them create or improve good health habits, like maintaining a healthy weight, improving their physical exercise or using mindfulness, calming or breathing practices for anxiety or stress relief.

While self-monitoring technology is useful for some people to monitor their condition, for others, wearable devices and continual monitoring can actually become a source of stress and anxiety – and anxiety can potentially make AFib symptoms worse. Some people find themselves frequently checking the device, limiting their activities or worrying about what each reading might include.  

Sometimes there also becomes too high a level of trust in wearable devices – inaccuracies can be introduced where the device doesn’t get a good reading due to poor contact or movement, and their technology is based on heart rates and single-lead ECGs, which are not accurate as a full 12-lead ECG. At times, I’ve found that certain notifications are alarming patients when there wasn’t an actual problem – like a slow heart rate that was detected during a deep sleep when this can be a completely normal pattern for some patients.

Dr Perel says, “it’s important that we interpret ECG and heart rate data in the context of understanding normal physiology, and take into account the various other factors which may cause inaccuracies. For some people, it can become too stressful to wear a device – and in those cases, the device may not be a good fit for that person.

Several smart watches with the ECG feature were approved by the TGA in Australia since 2021, and more continue to launch into the market. The Apple Watch Series is a market leader (and the first to be approved in May 2021). Other brands present in Australia includes Samsung watches and the Fitbit Sense.

Below are some options available and approved for consumers in Australia at the time of publication in January 2022.

According to Apple, the ECG feature that launched in its Watch Series 4 marked the first direct-to-consumer product in a smart watch that enabled customers to take an ECG right from their wrist, giving them the advantage of being first to market. The ECG app and the irregular rhythm notification feature were successfully included in the Australian Register of Therapeutic Goods (ARTG) in Australia as Class IIa medical devices in May 2021. 

The irregular rhythm notification feature on Apple Watch Series will check heart rhythms and send a notification if an irregular heart rhythm that appears to be AFib is identified.

According to Apple, the ability of the ECG app to accurately classify an ECG recording into AFib and sinus rhythm was validated in a clinical trial of around 600 participants, and the irregular rhythm notification feature was studied in the Apple Heart Study. With over 400,000 participants, the Apple Heart Study was the largest screening study on atrial fibrillation ever conducted, also making it one of the largest cardiovascular trials to date.

The Electrophysiologists at the AFib Institute are seeing great results from the Apple Watch.

“Apple Watches are more expensive than other products out there, however, we are seeing fantastic recordings from them. If the patient’s budget allows, an Apple Watch is a great option to consider,” said Dr John Hayes, Cardiac Electrophysiologist and Cardiologist and Director of Queensland Cardiovascular Group.

The latest Series, Apple Watch 8, includes a temperature sensor that enables advanced features for women’s health,and Crash Detection for severe car crashes.

According to Apple, people with AFib can also turn on the US FDA-cleared AFib History feature and access important information, including an estimate of how frequently their heart rhythm shows signs of AFib, providing deeper insights into their condition.

Users will receive notifications with an estimate from the previous week and also have access to a detailed history in the Health app on iPhone, including lifestyle factors that may influence AFib like sleep, alcohol consumption and exercise.

The AFib History feature in watchOS 9 has to date received a number of approvals from health authorities around the world including Australia.

Apple does explicitly publish some limitations in the the Apple Watch. The wording on its TGA application explicitly states: “The ECG data displayed by the ECG app is intended for informational use only. The user is not intended to interpret or take clinical action based on the device output without consultation with a qualified health professional.”  

Some concerns with the Apple Watch in the context of monitoring for Atrial Fibrillation, are that the capability for detecting AFib is reduced at heart rates above 120bpm – which can be common in episodes of Afib. There are also examples of both false-positive readings, and false negatives. The Apple Watch also does not take a constant reading of your ECG the whole time you are wearing it. It will take a reading approximately every two hours, depending on your activity levels. 

Samsung Electronics Australia announced in August 2021 that their Health Monitor application would launch in Australia and provide access to blood pressure tracking and TGA-approved ECG monitoring via its latest Galaxy Watch series. These are the first Samsung smartwatches available in Australia to offer both blood pressure and ECG monitoring. 

Samsung’s latest offering, the Samsung Galaxy Watch 5 features a 3-in-1 BioActive sensor controls three health sensors:

1. BIA: Monitor everything from body fat percentage (BIA) to skeletal muscle weight.
2. ECG: Real-time ECG tracking helps you stay in sync with your heart by measuring your heart rate and rhythm for any irregularities.
3. Optical Heart Rate Sensor: Monitor your heart rate and track your cardiovascular health to detect unusual heart rates and monitor your blood pressure.

The ECG feature is available on the Fitbit Sense 2, Fitbit Sense and Fitbit Charge 5 in Australia.The ECG app is also available on the Google Pixel Watch.

The Fitbit ECG app is made up of the Fitbit ECG app on the Fitbit wrist-worn product and the Heart Rhythm Assessment, which is a section in the Fitbit app on your phone or tablet. 

The Fitbit ECG app is used to create and record an ECG. The Fitbit ECG app analyses the recording and presents the results, and allows you to view your results on your phone or tablet.

While not a watch or wearable device, the KardiaMobile is a small sensor device that connects to your smartphone and can record an ECG.  

The KardiaMobile and KardiaMobile Card records a single-lead ECG, and the newer KardiaMobile 6L is the world’s only FDA-cleared, 6-lead personal ECG, which stands out as a leader from the rest of the single-lead wearables.  

According to AliveCor, the company behind the device, six leads mean 6 times the heart data, giving you and your doctor ‘the most detailed view of your heart you can get outside of a hospital.’ 

KardiaMobile 6L is available only with a KardiaCare membership, which offers exclusive features in the Kardia app. 

The device works differently from the smart watches – AliveCor’s proprietary technology converts electrical impulses from the user’s fingertips on both hands into ultrasound signals transmitted to the mobile device’s microphone. The six-lead version rests on your fingers of both hands, and is placed over the knee to record its ECG (see picture below). 

“AliveCor’s Kardia system is a little standalone module of Bluetooth in your phone and is reasonably priced. You do have to carry it with your phone, but that’s easily done,” said Dr John Hayes. 

Overall, the electrophysiologists at the QCG Atrial Fibrillation Institute unanimously agree that the TGA-approved options are largely effective and provide helpful data for discussion with their patients.  

“A lot of my patients just send their ECG recording to me, straight from their watch, or bring it with them when they come in to their appointment, and we have a look at the readings together. It is important that we review it together, and confirm we know what we are dealing with and that everything is as it should be, or if we need to keep recording,” explained Dr Hayes. 

While it is early days, there is plenty to be excited about. More and more digital health technologies and data-based algorithms are being created and brought to market.

“If we think about the Apple Heart Study, 400,000 patients uploaded their watch data, in the biggest study of its kind. Imagine what you can learn from half a million people’s heart data. This is a sign of things to come because you can learn a lot from that much data, and using machine learning or artificial intelligence to look at the data is fascinating,” Dr Perel said. 

“It will lead to whole new areas of innovation, understanding and management options for healthcare. It may enable people to access better care, faster – and the earlier we identify health conditions, or factors that lead to them, then the more options we may have to help or even prevent issues down the track. For example, you could discover what percentage of people get atrial fibrillation (including ‘silent atrial fibrillation), and correlate the heart data with other conditions. Over time you’ll be able to match that up with stroke rates and develop new options for intervention,” he said. 

“There are a lot of exciting opportunities that we will see come out of the growth of wearable HealthTech.”  

• https://www.wareable.com/health-and-wellbeing/ecg-heart-rate-monitor-watch-guide-6508
• https://news.samsung.com/au/samsung-announces-blood-pressure-tracking-and-tga-approved-electrocardiogram-ecg-monitoring-on-galaxy-watch-in-australia
• https://www.heartfoundation.org.au/research/world-heart-day
• https://www.apple.com/au/newsroom/2021/05/ecg-app-and-irregular-rhythm-notification-now-available-on-apple-watch/

• https://www.ahajournals.org/doi/10.1161/CIRCRESAHA.119.316342