#14: Wearing Your Heart on Your Sleeve
How wearables are bridging the gap between wellness and medicine.
Long used by athletes, wearables are now mainstream with almost 1 in 3 Americans owning a device for tracking health. But as the consumer wearable market grows, so does the demand for medical-grade accuracy and diagnostic capabilities.
Companies such as Apple and Fitbit have gained Class II FDA clearance for certain diagnostic tools, though not without trouble. Apple only narrowly avoided an import ban after battling a patent infringement case filed by med-tech company Masimo.
Other wearables such as WHOOP have stayed in their lane of fitness and wellness, explicitly stating their band isn’t an FDA-approved medical device for diagnosing illness. But during the COVID-19 pandemic, users counted on WHOOP to do just that.
In 2020, PGA tour player Scott Stallings praised his WHOOP for detecting his COVID-19 illness before he was symptomatic. The story went viral, prompting the PGA to equip over 1,000 players, caddies, on-site staff members, and media personnel with WHOOPs. That same year, Florida State University gave their female student-athletes WHOOP bands for 10 months, aiming to monitor and prevent the spread of COVID-19.
Consumers trust wearables for more than just counting steps. But do clinicians?
Listen to the Experts…
In July 2023, the Journal of the American College of Cardiology (JACC) released guidance for practicing cardiovascular clinicians on how to navigate integrating consumer wearable devices (CWDs) into clinical care. Below are my takeaways from the report’s discussion of health metric accuracy, how clinicians should interpret abnormal data, and health inequities in the use and accuracy of wearables.
Accuracy:
Heart Rate
Wrist-worn consumer wearables typically use photoplethysmography (PPG) technology. With PPG, smart devices can provide continuous heart rate data to users, though ECG chest straps are more accurate. Studies show variability among different PPG-based wearables that measure heart rate, thus making the data hard to interpret.
Some wearables underestimate heart rate. Others are less accurate for users during activity. The report suggests using chest straps to measure heart rate during exercise, which have better accuracy than wrist-worn technologies.
The American College of Cardiology recommends “interpreting consumer wearable device heart rate data based on the circumstances that prompted data collection”. They also recommend following up with a physician if there is a significant deviation in baseline heart rate.
Variability between different devices is less of an issue for users who generally only use one type of wearable to track heart rate.
Heart Rate Recovery (HRR)
HRR is a measure of how quickly your heart rate can get back to “baseline” immediately after exercising for a specified amount of time. This is a proxy for overall cardiac autonomic function and fitness.
There are no universally accepted values for HRR, but this metric is still used by clinicians to predict cardiac conditions. The report suggests that failure to achieve 12 beats/min reduction at one minute after exercise is the cutoff for risk stratification.
Heart Rate Variability (HRV)
Clinicians are increasingly using HRV to help diagnose heart disease, with patients with low HRV most at risk. However, lower HRVs may also be indicative of accumulated physiological stress and overtraining, most commonly seen in athletes.
HRV is highly individual, so for clinicians to even consider the data, patients must present with a longitudinal history of values.
Heart Rhythm
The AppleWatch and Fitbit Sense are among several wearable devices with FDA Class II (Medical Device) clearance for detecting atrial fibrillation—an irregular heartbeat. These devices use single-lead ECGs which when over-read by physicians, improve diagnostic performance.
Daily Step Count
Using wearables to track step count increases physical activity and lowers all-cause mortality and cardiovascular events. Though not useful for diagnostic purposes, clinicians can track the step count of patients to ensure better adherence to exercise prescriptions, leading to improved health outcomes.
According to the paper: “Consumer wearable devices have the possibility to promote physical activity and improve longevity, which may be extremely beneficial to high-risk populations”.
Peak VO2 Max
An indicator of longevity, peak VO2 max is an integrative metric reflecting cardiovascular, pulmonary, hematologic, and musculoskeletal system health. Though useful for assessing responses to therapeutic interventions and exercise performance, consumer wearables have significant error compared to cardiopulmonary exercise testing (CPET) which is the gold standard for peak VO2 max measurement.
Challenges of Interpreting Wearable Device Data:
Inaccuracies in data stem from the anatomic locations where users place consumer devices. Smart-watches and bands can be worn too tight or too loose or may shift during activity—all causes of inaccurate data.
Whether wearable data is suggestive or diagnostic, clinicians are thinking about the best way to integrate these devices into patient care. For now, the American College of Cardiology has come out with the following framework for interpreting wearable data:
J Am Coll Cardiol: Consumer Wearable Health and Fitness Technology in Cardiovascular Medicine: JACC State-of-the-Art Review
Health Equity:
“Consumer wearable device users are more likely to be younger, White, wealthier, and of higher educational status compared with people without devices”.
What’s more, there are significant limitations with respect to PPG technology for people with darker skin tones.
“CWDs using PPG to measure health metrics have the potential to exacerbate existing structural health disparities and contribute to structural racism by failing to account for differences between patients like skin pigmentation. As our society continues to embrace CWDs, ongoing focus on equity concerns will be required in efforts to close the existing digital divide and to avoid the risk of access to CWDs becoming another social determinant of health.”
WearableMD
Wellness is the active pursuit of health.
Medicine is the science and art of dealing with the maintenance of health and the prevention, alleviation, or cure of disease.
Device makers are required to distinguish between the two definitions. Apple’s blood oxygen measuring capabilities, for example, are classified under health and wellness, but its ECG app is listed as a medical device.
To say that just because a metric is considered “health/wellness” information it does not fall within the scope of medicine is backward. Modern medicine has already failed to prioritize wellness and prevention over treatment and cures, leading to 6 out of every 10 adults in the US suffering from chronic disease.
Despite a line being drawn between wellness and medicine, both types of data can help inform patient care. And if prevention is the future of healthcare, then that line should be permeable.
Today, patients prefer clinicians who integrate consumer wearables into care plans. Tomorrow, they will require it.
This week in healthcare:
Amazon Health Launches New Initiative To Address Chronic Conditions, Forbes
Silicon Valley’s Quest to Live Forever Has Many Warring Factions, Bloomberg
How Digital Health Fundraising Took On a Different Shape in 2023, MedCity News
A Public Health Approach to New York City’s Mental Health Crisis, JAMA
Wearables combined with an much more robust AI layer capable of weeding out false positives will make a great backbone for remote health monitoring. It will more personalization and early prediction possible.