Can wearables reliably detect signs of atrial fibrillation? FDA says yes to Fitbit

Wearable smartwatches can alert users to signs of atrial fibrillation and prompt them to seek health professional advice, but subsequent management remains to be better defined

Article by Debra Kiss, PhD; Senior Medical Writer at EPG Health

Another wearable smartwatch, Fitbit, joins Apple in gaining FDA clearance for its algorithm to passively detect signs of atrial fibrillation using photoplethysmography (PPG) technology.

• What evidence supports its use in detecting irregular heart rhythm?
• Do the benefits outweigh the risks?
• What can healthcare professionals do with this information?

In April 2022, Google and Fitbit announced they received FDA clearance for their algorithm to passively detect atrial fibrillation (AF) while the user is at rest or sleeping¹, a feature which will soon be available across a range of Fitbit’s heart-rate enabled devices¹.

While the Fitbit device obtains heart rate data using an optical photoplethysmography (PPG) sensor on the user’s wrist, the software algorithm passively assesses this heart rhythm data for irregularities and signs of AF. If it detects an abnormality suggestive of AF, the user receives an irregular heart rhythm detection (IHRD) notification and is prompted to see their healthcare provider for further investigation¹. This development follows Apple’s 2018 FDA clearance for their PPG-based irregular heart rhythm notification feature on the Apple Watch². Across both the Fitbit and Apple Watch, these PPG-based features accompany on-demand ECG readings which are available through their respective ECG apps^{1, 3}.

Considering up to one-third of individuals with AF are asymptomatic⁴, passive detection of irregular heart rhythm and an early prompt to see a healthcare professional for AF assessment have tremendous potential to save lives, expedite AF detection, and maybe even prevent related complications such as stroke. But what does the data say?

Can Fitbit’s PPG-based algorithm reliably detect potential AF?

The key clinical validation data for Fitbit’s algorithm came from the large-scale Fitbit Heart Study, which was a prospective single-arm remote clinical trial of more than 450,000 US participants over 22 years of age⁵. The rationale and design of this study was published in 2021⁶, however the results of the study are yet to be published in a peer-reviewed journal. Rather, a conference presentation from American Heart Association’s Scientific Sessions in 2021⁵ has been widely been cited as key evidence for clinical validation of the Fitbit PPG algorithm¹.

According to the 2021 AHA abstract, PPG data from Fitbit Heart Study participants were analysed centrally using the software algorithm, which examined overlapping 5-minute pulse tachograms during inactivity. An irregular heart rhythm detection (IHRD) notification was triggered after 11 consecutive irregular tachograms⁵. Those with an IHRD notification were invited to schedule a visit with a telehealth provider, and eligible individuals were sent a one-week ECG patch monitor and invited to schedule a follow-up telehealth visit.

The abstract reported encouraging results for the positive predictive value (PPV) of the IHRD notification feature, indicating the majority of patients (98.2%) who received a IHRD notification had clinically-detectable AF confirmed by an ECG monitor⁵. A higher rate of IHRD notifications were observed in the group aged ≥65 years (4%; 2070 patients), in which the IHRD PPV remained high at 97.0% (95% CI 91.4%-99.4%)⁵. Although these results look promising, limited data were available in the conference abstract, and we look forward to seeing the full study results in a peer-reviewed publication, once it becomes available.

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

There are numerous benefits to the use of wearables for passive heart rhythm monitoring, including the identification of individuals at high risk for AF based on early detection of an irregular heart rhythm⁷, earlier treatment and preventative interventions – all of which have tremendous potential to improve health outcomes. Furthermore, wearables have been associated with positive lifestyle changes such as increased daily step count, physical activity and weight loss⁸, which may also help to reduce a person’s 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, false-positives may result in over-utilisation of healthcare resources to manage patients with no clinically detectable signs of AF, and may cause anxiety^{9, 10}. Although concerns have been raised about false-positive abnormal heart rhythm notifications from the Apple Watch⁹, the high PPV reported in the Fitbit study indicates a low number of false positives⁵ (However, the rate of false positives in the Fitbit study remains to be confirmed once the full peer-reviewed publication becomes available).

Overall, considering the morbidity and mortality associated with undiagnosed AF, including an increased risk of stroke⁷, 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.

Management of PPG-based irregular heart rhythm notifications in practice

For individuals who receive a PPG-based irregular heart rhythm notification, an ECG assessment is required to confirm a clinical diagnosis of AF (e.g. via 12-lead ECG, Holter monitoring, etc.)^{4, 11, 12}.

But what if potential AF is indicated by ECG readings from a mobile or wearable device? Well, if an ECG recording of ≥30 seconds indicates AF on a validated mobile or wearable device, this data could be used to establish an AF diagnosis in particular circumstances – for example, if the data has been manually reviewed by a physician with appropriate expertise in ECG rhythm interpretation, and considered sufficient for diagnosis¹¹. However, caution is advocated with wearables, as not all are clinically validated, and there is a need for more large, high-quality, randomised studies in this fast-moving field ^{4, 11}. If there is any uncertainty about the quality or interpretation of device-based ECG readings, a confirmatory ECG assessment is recommended¹¹.  

Although the 2020 European Society of Cardiology (ESC) guidelines highlighted the value of wearables in substantially adding to diagnostic opportunities for those at risk for AF, they also noted appropriate management pathways for these and other novel devices were still incompletely defined¹¹. Furthermore, the most recent NICE guidance on diagnosis and management of AF did not incorporate wearable technology in their diagnostic pathway^{4, 12}. It remains to be seen if later guidelines or consensus statements will help to address this gap.

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.

Find out more about screening for AF and recommendations on wearable technology

References

1. Google. New Fitbit feature makes AFib detection more accessible. Available at: https://blog.google/products/fitbit/irregular-heart-rhythm-notifications/. Accessed 26 April 2022.
2. US Food and Drug Administration. De novo classification request for irregular heart rhythm notification feature (DEN180042, Apple Inc). 8 August 2018 2018. Available at: https://www.accessdata.fda.gov/cdrh_docs/reviews/DEN180042.pdf. Accessed 26 April 2022.
3. Apple. Apple. ECG app and irregular heart rhythm notification available today on Apple Watch. 6 December 2018. Available at: https://www.apple.com/newsroom/2018/12/ecg-app-and-irregular-heart-rhythm-notification-available-today-on-apple-watch/. Accessed 5 May 2022.
4. Briosa e Gala A, Pope MT, Leo M, Lobban T, Betts TR. NICE atrial fibrillation guideline snubs wearable technology: a missed opportunity? Clin Med (Lond). 2022;22(1):77-82.
5. Lubitz SA, Faranesh A, Selvaggi C, Atlas S, McManus D, Singer D, et al. Detection of Atrial Fibrillation in a Large Population using Wearable Devices: The Fitbit Heart Study. LBS.04. Presented at the American Heart Association Scientific Sessions 2021. Virtual. Available at: https://www.abstractsonline.com/pp8/?_ga=2.141042993.2042594723.1635046736-1021258137.1633710264#!/9349/presentation/18161.
6. Lubitz SA, Faranesh AZ, Atlas SJ, McManus DD, Singer DE, Pagoto S, et al. Rationale and design of a large population study to validate software for the assessment of atrial fibrillation from data acquired by a consumer tracker or smartwatch: The Fitbit heart study. Am Heart J. 2021;238:16-26.
7. Kreimer F, Mügge A, Gotzmann M. How should I treat patients with subclinical atrial fibrillation and atrial high-rate episodes? Current evidence and clinical importance. Clin Res Cardiol. 2022.
8. Ringeval M, Wagner G, Denford J, Paré G, Kitsiou S. Fitbit-Based Interventions for Healthy Lifestyle Outcomes: Systematic Review and Meta-Analysis. J Med Internet Res. 2020;22(10):e23954.
9. Wyatt KD, Poole LR, Mullan AF, Kopecky SL, Heaton HA. Clinical evaluation and diagnostic yield following evaluation of abnormal pulse detected using Apple Watch. JAMIA. 2020;27(9):1359-1363.
10. US Preventive Services Task Force. Screening for Atrial Fibrillation: US Preventive Services Task Force Recommendation Statement. JAMA. 2022;327(4):360-367.
11. Hindricks G, Potpara T, Dagres N, Arbelo E, Bax JJ, Blomström-Lundqvist C, et al. 2020 ESC Guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS): The Task Force for the diagnosis and management of atrial fibrillation of the European Society of Cardiology (ESC) Developed with the special contribution of the European Heart Rhythm Association (EHRA) of the ESC. Eur Heart J. 2021;42(5):373-498.
12. National Institute for Health and Care Excellence. Atrial fibrillation: diagnosis and management: NICE guideline [NG196]. 2021. Available at: www.nice.org.uk/guidance/ng196. Accessed 26 April 2022.