Smartwatch health data are piling up. How can doctors keep pace?

Wearable devices that can track health data offer a promising new research frontier, but a journal case study published in 2020 illustrates one of their core problems¹.

The study describes a 70-year-old woman with paroxysmal atrial fibrillation — bouts of fast, irregular heartbeat that can be symptomatic or silent. This form of atrial fibrillation often resolves without treatment, but because of the patient’s other risk factors for stroke, her doctors put her on anticoagulant medication to lower the chance of a deadly blood clot.

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The patient wore a smartwatch that included an app for monitoring heartbeat and generating electrocardiogram (ECG) readouts. In the year following her diagnosis, she checked those ECG readouts 916 times. She turned up to one consultation with her electrophysiologist — clinicians who specialize in arrhythmia — with a printed stack of those ECGs, according to Lindsey Rosman, who co-authored the paper describing the case.

“When I say stack, I mean hundreds,” says Rosman, a clinical health psychologist at Northwestern University in Chicago, Illinois.

This example illustrates the huge challenge that wearable devices — often not approved for medical use and now being worn by hundreds of millions of people globally — are posing in terms of the vast amount of data they produce. Patients, clinicians and researchers are increasingly having to make sense of this growing mountain of information, whether from approved or non-approved devices, without getting overwhelmed. But if this can be overcome, there are potentially groundbreaking applications for consumer devices, or clinically developed ‘medical-grade’ wearables, in diagnosing, managing or preventing heart conditions, neurological disorders and metabolic diseases.

Monitoring and managing

From the perspective of doctors who specialize in heart-rhythm disorders, devices such as smartwatches present an extraordinary technological opportunity. “For the first time, we could monitor our patients for long periods with inexpensive devices,” says Rod Passman, a cardiac electrophysiologist and director of the Center for Arrhythmia Research at Northwestern Medicine in Chicago, Illinois.

That’s especially useful in atrial fibrillation, in which a chronic or worsening irregular heartbeat raises the risk that blood will pool in the left atrium and form a clot that can travel to the brain and cause a stroke. Around one in three people with atrial fibrillation will experience a stroke, so are put on blood-thinning medication for life. But anticoagulants come with side effects, including the risk of excessive bleeding.

Despite the variability in the severity of the condition, and the availability and use of other treatments and prevention, Passman says “we have this paradigm where if you have atrial fibrillation and other risk factors, you’re on a blood thinner for life, regardless of whether your episodes are once a day, once a year, or you’ve lost weight or had an ablation, and the atrial fibrillation is gone”.

Passman and colleagues are investigating whether it’s possible to use wearables to monitor the frequency of episodes and adjust treatment accordingly. In their REACT-AF trial, a multi-centre US-based trial run out of Northwestern University in Chicago, patients with atrial fibrillation are randomized either to stay on their usual dose of anticoagulants or to wear a smartwatch with an app that will alert them when they need to restart medication temporarily. Many smartwatches can already measure heart rate, either with photoplethysmography — which uses light to detect changes in blood volume — or electrocardiography, a simple version of the ECG monitors used in clinical settings. The innovation here is the app that interprets those signals.

“We expect to show that this strategy is equally effective at preventing stroke,” Passman says. “But because patients are on blood thinners a fraction of the time, they will have less bleeding, they’ll pay less for medication, and we expect an improvement in life quality.”

There’s interest in whether wearable devices could be used to screen for and predict undiagnosed heart arrhythmias, including rare ones linked to sudden arrhythmic death syndrome. Each year, in the United States, around 4,000 children and young adults die from a heart arrhythmia. Sudden arrhythmic death syndrome is caused by a range of often inherited disorders, many of which are asymptomatic. In many cases, the first warning is also the last.

One review² found evidence that consumer smartwatches could detect a range of arrhythmias beyond atrial fibrillation, but warned of the risk of false positives due to inaccurate readings. Smartwatches aren’t being used routinely to identify at-risk patients because they haven’t been shown to be effective, Passman says. But with millions of people wearing the devices, the medical potential is clear.

Although doctors and researchers are more cautious with the idea of using standard consumer smartwatches as a screening and diagnostic tool, consumers have fewer hesitations. Rosman says patients are increasingly sending smartwatch readouts about their heart, stress levels or even sleep patterns to their doctor via patient portals, bringing them along to consultations, or rushing to the emergency department because of an alert from their device.

Sometimes wearable devices do turn up something useful. Passman says patients have received a diagnosis of an arrhythmia because their smart device alerted them that something was wrong. But that doesn’t necessarily translate into better health outcomes. “While it makes intuitive sense that that would be a great thing to do because we’d find atrial fibrillation early — we would get patients on blood thinners and prevent strokes — we’ve yet to prove that’s the case,” he says.

The three-year Heartline study³, funded by Apple and pharmaceutical company Janssen, aims to do that. US researchers are recruiting around 28,000 people across the country aged 65 or older — some with atrial fibrillation, and some without — to see whether early detection or monitoring of symptoms using an Apple Watch improves cardiovascular outcomes.

Another arena where the ubiquity of wearable devices is opening up a new paradigm of management and treatment is in neurology. Consumer smartwatches are already widely used for the detection of falls, which can result from frailty or neurological conditions; one controlled trial in 22 healthy adults⁴ found that they correctly identified 77% of falls with a false-positive rate of 1.7%. But there’s growing interest in their application for monitoring and alerting wearers or their carers to seizures.

“Seizures are traditionally reported based on others witnessing the event,” says paediatric neurologist Anup Patel, from Nationwide Children’s Hospital in Columbus, Ohio. People who are alone at the time of their seizure might be unaware they have had one.

There are a small number of specialized regulator-approved seizure-detection wearable devices available in the United States and Europe. Patel says these approved devices, which can include arm bands and patches, are increasingly being used in clinical trials to provide more accurate information. But he has concerns about the accuracy of detection, suggesting that the algorithms on approved medical devices — which analyse movement, temperature and heart rate — might only be around 90% accurate, with a risk of false-positive alerts. In his experience, families often start using a seizure-alert device, but stop because of the false positives.

Another barrier to more widespread use of such seizure-monitoring devices is that they are more obviously a medical device, not a familiar consumer device such as a smartwatch, and that could attract stigma and attention. So patients might prefer consumer devices if they can provide the same service.

Another scenario that is generating a lot of interest is whether wearable consumer devices such as smartwatches could be used to flag an impending seizure so people can get to a safe position, or take medication that could prevent or mitigate an attack. “Are there biometric parameters that can help to say, ‘When X, Y, Z happens, you’re going to have a seizure’,” Patel says.

This isn’t unique to epilepsy; there could be a range of scenarios in neurology, or even across the spectrum of disease, in which a wearable device could warn wearers if they are at higher risk of some kind of adverse event; a migraine, for example. “Are there parameters that we can have ahead of time to say, ‘You’re at risk for a fall,’ or ‘Today’s a bad day to go out, you may want to take it easy’?” he says.

With all of these potential uses for wearables, a key issue is how they can be integrated into health-care systems to make a difference at a population level. Clinicians have the expertise to handle the wealth of information that devices produce, but they’re in a bind: what is their responsibility when it comes to unregulated data from an unapproved device sent to them outside hours by a worried patient?

Patel says that early on, there was a concern that doctors might face litigation if they didn’t review these data promptly and a patient then experienced an adverse health event. “Largely, that fear has been relieved because it’s not the case, and there are clear parameters that say no, you are not liable for that,” he says.