Wearable digital health technology (DHT) is becoming increasingly popular, allowing wearers to track variables such as physical activity, sleep, and other physiological data.

Ranging from smartwatches to adhesive sensor-containing patches, wearable DHT has the potential to become integrated into cardiovascular medicine, with applications ranging from remote monitoring of chronic conditions to arrhythmia screening currently being assessed.

Hughes A, Shandhi MMH, Master H, et al. Wearable devices in cardiovascular medicine. Circulation Res. 2023;132(5):652–670.

 

 

 

Relevant biomedical variables

 

According to an article published in New England Journal of Medicine, approximately 45% of Americans wore a smartwatch as of April 2022, with 92% of users reporting that they utilize the device for health-maintenance purposes.

Friend SH, Ginsburg GS, Picard RW. Wearable digital health technology. N Engl J Med. 2023;389(22):2100–2101.

Overall, the market for wearable DHT is estimated to grow to 76 billion by the year 2028.

 

While cardiovascular disease (CVD) symptoms vary from person to person, the primary culprits include arrhythmia, high blood pressure, coronary artery-valve damage, and stroke.

• Physical activity: Wearable DHT that measure physical activity include pedometers, load transducers, and accelerometers.

• Sleep: Poor sleep is directly correlated with incidence of CVD. Electroencephalography (EEG) and photoplethysmography (PPG) are the two most common technologies for monitoring sleep.

• Heart rate: In a clinical setting, heart rate is assessed by analyzed electrocardiogram (ECG) signals, whereas in the fitness setting, it is assessed during exercise using PPG.

• Pulse rate variability: Unexpected variations in pulse rate variability can aid in the diagnosis of CVD.

• Blood pressure: Pulse transit time, which can be obtained from ECG and PPG monitoring, can be used to estimate blood pressure.

• Blood oxygen saturation: Pulse oximetry, which is based on the PPG technique, is used to assess how much oxygen is in the blood.

• Blood glucose: Wrist-worn devices, based on the technique of reverse iontophoresis, can be used to measure blood glucose in a non-invasive manner.

• Blood cholesterol level: Electrochemical biosensors show potential in overcoming the shortcomings of traditional approaches for measuring cholesterol without compromising accuracy.

And even newer technologies are currently in development. For example, researchers from the Southern University of Science and Technology in China have developed a wearable photoacoustic watch.

According to the Biosensors review, wearable DHT can typically read more than one biomedical variable, with the main biomedical variables for CVD monitoring being heart rate, blood oxygen saturation, and ECG.

In comparison to commercial wearable DHT, non-commercial wearable devices are typically developed for monitoring only arrhythmia and heart failure.

 

 

Accuracy

 

Before wearable DHT can be integrated into routine clinical practice, it is critical to ascertain the reliability of the data obtained from these devices.

A systematic review published in the Journal of Medical Internet Research assessed the accuracy and acceptability of 72 commercial wearable devices.

Germini F, Noronha N, Borg Debono V, et al. Accuracy and acceptability of wrist-wearable activity-tracking devices: systematic review of the literature. J Med Internet Res. 2022;24(1):e30791.

The evidence base for this analysis was made up of a total of 65 articles and 14 outcomes, including step counts, heart rate, and energy expenditure. Investigators found significant clinical heterogeneity among the various devices.

 

For step counts, the Fitbit Charge, or the Fitbit Charge HR, had a mean absolute percentage error (MAPE) of less than 25% across 20 studies. The accuracy of the devices was compared to manual counts, automated counts through video analysis, an activity tracker, or a photoelectric cell. For heart rate, the Apple Watch had a MAPE of less than 10% across two studies. For heart rate, the reference standards that were utilized included electrocardiograph and pulse oximetry. For all tested brands, the MAPE was greater than 30% for energy expenditure.

However, the use of PPG to measure heart rate in different populations has recently been called into question.

A 2020 article published in npj Digital Medicine measured heart rate from consumer-grade as well as research-grade wearables across skin tones and during various activity levels. Researchers did not observe statistically significant differences in accuracy depending on skin tones. However, the absolute error for the wearable devices was approximately 30% higher during activity than at rest.

Bent B, Goldstein BA, Kibbe WA, et al. Investigating sources of inaccuracy in wearable optical heart rate sensors. npj Digit Med. 2020;3(18).

 

 

Successes and challenges

 

As an example of how wearable DHT can be integrated into cardiovascular clinical care, a study published in NEJM demonstrated that the Apple Watch detected atrial fibrillation in 34% of participants who received an alert of an irregular heartbeat and subsequently wore an ECG patch. Overall, 84% of the notifications of irregular pulse were consistent with atrial fibrillation.

Perez MV, Mahaffey KW, Hedlin H, et al. Large-scale assessment of a smartwatch to identify atrial fibrillation. N Engl J Med. 2019;381(20):1909–1917.

 

 

1. Data ownership: As there are multiple stakeholders, including device manufacturers, healthcare providers, and patients, who owns the data becomes important.

2. Patient trust, literacy, and access: Robust security protocols need to be in place, as patients may be worried their personal health data may be compromised.

3. Standards and interoperability: There needs to be a clear, universal set of standards for wearable DHTs rather than allowing each device manufacturer to establish their own standards.

4. Integration into clinical environments: Wearable DHTs generate large data sets. A challenge that needs to be addressed is how to integrate these data sets into current clinical practice.

5. Patient empowerment and agency: By wearing DHTs, will patients feel empowered to play an active role in their own health?

6. Reimbursement and ROI for healthcare systems: For wearable DHTs to be integrated into clinical practice, healthcare systems need to make investments in infrastructure, data analytics, and cybersecurity.