On the pulse: Smartwatches for AFib

Since 2018, the Apple Watch and other smartwatches from brands including Fitbit, Garmin, Samsung, Verily and Withings have received US Food and Drug Administration (FDA) clearance to detect irregular heart rhythm or other signs of atrial fibrillation (AF) using technologies such as photoplethysmography (PPG) and/or single-lead electrocardiogram (ECG).^1-6

Considering up to one-third of individuals with AF are asymptomatic,⁷ passive monitoring for irregular heart rhythm and early prompts to seek medical advice for AF assessment could potentially save lives, expedite AF detection, and possibly prevent related complications such as stroke. But are these devices accurate, and how does their AF detection compare?

Can PPG-based readings reliably detect potential AF?

Various smartwatches, such as those from Apple and Fitbit, use a PPG sensor that indirectly measures heart rate by continuously monitoring changes in blood flow through the wrist while at rest or sleeping. They alert users to abnormalities suggesting AF, prompting them to consult their healthcare provider for further investigation.^1,2,8 Across both the Apple and Fitbit smartwatches, these PPG-based monitoring features accompany on-demand ECG readings through their ECG apps.^2,8

The initial FDA clearance for the Apple Watch in 2018 was based on an early subset of data from the Apple Heart study.^1,8

• Across 226 participants with analysable data, the positive predictive value of spot irregular tachograms to detect AF was only 66.6%¹
• The secondary analysis showed the notification-level PPG for AF in an enriched population was 78.95%, and this was considered to support the Apple Watch’s effectiveness for AF detection using PPG data¹

For Fitbit, the 2022 FDA clearance for its PPG analysis software algorithm was based on results of the large-scale Fitbit Heart Study, a prospective single-arm remote clinical trial of more than 455,000 US participants over 22 years of age.⁹

Of the 4,728 participants (1%; 4728/455,699) who received an irregular heart rhythm detection (IHRD) notification on the Fitbit, the majority (98.2%) had clinically detectable AF confirmed by an ECG monitor⁹

Of those who received an IHRD notification, attended the telehealth visit and responded to a survey at the end of the study (n=733), 33.1% (256) received a new diagnosis of AF and 21.3% (165) started a new medication to treat AF.

How does AF detection compare across different smartwatches?

A small real-world comparative study (N=201) assessed the accuracy of AF detection across four smartwatches (including those from Apple, Samsung, Withings and Fitbit) and one mobile device (AliveCor) in 2023.¹⁰

• Compared with a 12-lead ECG, the Apple and Samsung watches achieved the same sensitivity and specificity for AF detection (85% and 75%, respectively, for both watches), while results for Withings were 58% and 75%, and Fitbit’s were 66% and 79%, respectively
• Rates of inconclusive tracings were highest for AliveCor (26%) and lowest for Samsung (17%)
• Overall, manual review of tracings was required in about 25% of cases

In addition, the Verily Study Watch is a prescription-only, medical grade device that was not included in the real-world comparative study above, and was FDA cleared for continuous monitoring of AF in 2019.^5,11 Its clinical-grade performance for AF detection was demonstrated in a small prospective multicentre study of people with paroxysmal AF (N=117), which reported a 96.1% sensitivity and 98.1% specificity for interval-level AF detection versus a reference patch ECG.¹¹

Benefits and drawbacks: Early detection of AF vs over-utilisation of healthcare

Through passive heart rhythm monitoring, smartwatches can help to identify individuals at high risk of AF through early detection of irregular heart rhythm.¹² This may lead to earlier treatment and preventive interventions, and has potential to improve health outcomes. Additionally, wearables are associated with positive lifestyle changes including increased daily step count, physical activity and weight loss,¹³ which can lower the risk of heart conditions and associated complications.

But what are the risks and drawbacks of using wearables to detect signs of AF? Users of wearables may not always fit the device appropriately on their wrist, which may lead to inaccurate readings. In addition, misinterpretation or false-positives may result in over-utilisation of healthcare resources and cause anxiety in people without clinical signs of AF.^14-16

Overall, considering the morbidity and mortality associated with undiagnosed AF, including an increased risk of stroke,¹² perhaps the potential for early identification of AF is worth the risks for individuals who choose to adopt wearables. In the meantime, more high-quality, large and randomised studies will help to shed light on this issue.

How are irregular heart rhythm notifications from smartwatches managed in practice?

Smartwatches that are FDA-cleared to detect irregular heart rhythm or signs of AF are intended for screening or prediagnosis purposes, and are not intended for clinical decision-making¹¹
 

The 2022 European Heart Rhythm Association (EHRA) consensus clarified that AF diagnosis requires confirmation via ECG with clinician oversight, and ECG tracings from smartwatches still require physician oversight and analysis for rhythm diagnosis.¹⁷

Therefore, people with irregular heart rhythm notifications from their smartwatch should discuss these findings with their healthcare professional to determine whether further ECG investigation is required to investigate and diagnose potential arrythmias, such as AF.

Note: This article is provided as general information only. Refer to your local clinical guidelines for the most current and specific recommendations on screening, diagnosis and management of AF.

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