By Sarah Handzel, BSN, RN
For better or worse, smart devices that monitor various aspects of health have been integrated into society. In 2021, the Pew Research Society found that 21% of Americans used smartwatches or other wearable fitness trackers, and the number has continued to climb since then.1 As technology improves, more people are using products featuring wearable ECG devices to monitor their cardiovascular health in particular.
While it's true that such devices can give important insight into a person's health status, not all are created equal. Many cardiologists question the accuracy of the devices, while others believe these tools may be useful in the diagnostic process. Regardless of opinion, wearable ECG devices have already empowered many consumers to take greater charge of their own health.
ECG Wearable Devices
Currently, there are numerous digital ECG devices available to consumers. Many smartwatches and other fitness trackers feature single-lead ECG, as do wearable patches and chest straps. Many of these products also pair with apps that store ECG tracings, which can be shared with physicians remotely.
Other wearables, such as patches, adhere to the skin, are water-resistant and wireless, and are generally well tolerated from a patient perspective. Some patches offer up to 30 days of continuous monitoring, collecting large amounts of data for cardiologists to sort through.
These devices appeal to consumers because they are easy to use, relatively inexpensive, and offer insight into the state of an individual's cardiovascular health. However, not all wearable devices are cleared by the FDA. In other words, not all have demonstrated the same effectiveness and accuracy as other rhythm-monitoring devices, such as the standard 12-lead ECG.
Sensitivity and Specificity
A large determinant of wearable ECG devices' value comes down to the device's sensitivity and specificity.2 Sensitivity, or the ability of a test to correctly identify patients with a disease, varies greatly between wearable devices. Device specificity—or the ability to rule out patients who do not have a specific disease—is also an important consideration.
Unfortunately, many wearable ECGs have high sensitivity and low specificity—that is, they catch a large number of false positives because they cannot differentiate them from true positive results. This presents a significant problem, as specificity becomes more important in populations with low disease prevalence.
A variety of studies have questioned the accuracy of consumer devices for several cardiac conditions, such as Afib, with mixed results. One meta-analysis in the Journal of Atrial Fibrillation found conflicting results among included studies; depending on the study criteria, smartwatches either statistically oversensed or undersensed Afib among study participants. However, the ultimate conclusion of the meta-analysis suggests that there is no significant difference in Afib detection between smartwatches and composite ECG monitoring, Holter monitoring, patch monitoring, and loop recorder.3
According to a review in Nature Reviews Cardiology, single-lead ECGs can help diagnose simple, common arrhythmias like Afib.4 However, they are not useful in diagnosing more complex arrhythmias and other conditions, such as myocardial infarction. Another study in Frontiers in Cardiovascular Medicine compared three wearable ECG devices to conventional 12-lead ECG. In the study, Apple and Samsung smartwatches demonstrated 87% and 88% sensitivity respectively.5 Another device, the Withings smartwatch, demonstrated 78% sensitivity. However, these numbers improved when the researchers excluded non-classified ECGs. An ECG was considered non-classified if the recording was poor or inconclusive, or if the patient's heart rate was less than 50 beats per minute.
Other wearables demonstrate greater sensitivity and specificity. For example, a recent article in the Journal of Cardiovascular Pharmacology and Therapeutics evaluated smartphone-based ECG recordings intended to help diagnose Afib. The device evaluated, KardiaMobile, was used in conjunction with a dedicated smartphone app. According to data gathered from almost 500 participants aged 65 or older, sensitivity and specificity were 100% and 98.7%, respectively.6
To learn more about the power of the ECG in today's clinical landscape, browse our Diagnostic ECG Clinical Insights Center.
Managing Data Overload
Beyond accuracy concerns, many cardiologists should also note that single-lead ECG devices like smartwatches generate tremendous amounts of raw data that must be interpreted professionally. Technology companies have begun to explore machine learning techniques that could help physicians arrive at accurate and timely diagnoses.
This presents a significant challenge. While algorithms used to interpret ECGs are governed by a standard set of parameters, there is no recognized standard for tuning these algorithms. Smartwatches and other wearable ECG products should only use algorithms based on the device's intended purpose. In interpreting test results, clinicians will need to account for this and other factors, which could impact the quality of the data collected.
Many cardiologists still rely on their professional experience to interpret ECGs, including those collected by wearable devices. This mountain of information could become overwhelming as physicians struggle to keep up with consumer demand for health data. As one review in Current Cardiology Reports notes, algorithms governed by parameters like sensitivity, specificity, and positive and negative predictive values may be useful.7 However, clinicians must still account for the characteristics of the algorithms when they interpret the data.
Trusting Wearable ECG Devices
Wearable devices featuring ECG may be used alongside other, more established diagnostic tools, such as 12-lead ECG. While wearables do provide important information that clinicians can use, they only show a small piece of the overall picture of the patient's health status.
Physicians who choose to use information gathered from such technology should be aware of its limitations. They should also be comfortable discussing these limitations with patients in order to appropriately incorporate such devices into treatment plans. As one review in the European Journal of Heart Failure notes, clinician overreading is still mandatory for accurate diagnoses.8
Until such time as machine learning algorithms demonstrate total accuracy in diagnosing various cardiac conditions, physicians should remain skeptical about using wearable ECG devices as the sole diagnostic tool. The data gathered by these devices can be useful, but it is no substitute for a standard 12-lead ECG in making a diagnosis.
References:
- Vogels EA. About One-in-five Americans use a smartwatch or fitness tracker. Pew Research Center. https://www.pewresearch.org/fact-tank/2020/01/09/about-one-in-five-americans-use-a-smart-watch-or-fitness-tracker/. Accessed August 14, 2022.
- Swift A, Heale R. What are sensitivity and specificity. BMJ Journals: Evidence-Based Nursing. November 12, 2019. 23:2-4. https://ebn.bmj.com/content/23/1/2.
- Mehmet AE, Young D, Kanuri SH, et al. Diagnostic utility of smartwatch technology for atrial fibrillation detection - a systematic analysis. Journal of Atrial Fibrillation. Apr-May 2021. 13(6): 20200446. doi: 10.4022/jafib.20200446.
- Bayoumy K, Gaber M, Elshafeey A, et al. Smart wearable devices in cardiovascular care: Where we are and how to move forward. Nature Reviews Cardiology. March 4, 2021. 18;581–599. https://doi.org/10.1038/s41569-021-00522-7.
- Abu-Alrub S, Strik M, Ramirez DF, et al. Smartwatch electrocardiograms for automated and manual diagnosis of atrial fibrillation: A comparative analysis of three models. Frontiers in Cardiovascular Medicine. February 4, 2022. 9:836375. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8854369/
- Zaprutko T, Zaprutko J, Baszko A, et al. Feasibility of atrial fibrillation screening with mobile health technologies at pharmacies. Journal of Cardiovascular Pharmacology and Therapeutics. 2020;25(2):142-151. https://doi.org/10.1177/1074248419879089.
- Al-Alusi AM, Ding E, McManus DD, et al. Wearing your heart on your sleeve: the future of cardiac rhythm monitoring. Current Cardiology Reports. November 25, 2019. 21:158. https://doi.org/10.1007/s11886-019-1223-8.
- Haverkamp W, Javed Butler J, Anker SD. Can we trust a smartwatch ECG? Potential and limitations. European Journal of Heart Failure. April 20, 2022. 23(6): 850-853. https://doi.org/10.1002/ejhf.2194.
Sarah Handzel, BSN, RN, has been writing professionally since 2016 after spending over nine years in clinical practice in various specialties.
The opinions, beliefs, and viewpoints expressed in this article are solely those of the author and do not necessarily reflect the opinions, beliefs, and viewpoints of GE Healthcare. The author is a paid consultant for GE Healthcare and was compensated for creation of this article.
