Research shows the Apple Watch can detect an early sign of heart disease

The Apple Watch has
already saved lives
with its heart rate-monitoring, but
it’s often unintentional. A person might feel symptoms like
dizziness or shortness of breath, then check their heart rate
to confirm something weird is going on. A team of researchers
just proved that the watch’s heart rate sensor can actually
detect an early sign of heart disease without any symptoms at
all, a development that could change how people use their Apple
Watches.

The Apple Watch’s heart rate sensor can accurately pick up
atrial fibrillation, an abnormal heart rate that can lead to
stroke or heart disease. Atrial fibrillation can be caused by a
variety of factors, including high blood pressure, so the Apple
Watch isn’t a diagnostic device. But its accurate heart rate
sensor shows there is potential for the watch as a
health and fitness tool
beyond its basic fitness-tracking
features.

Developers of the Apple Watch app
Cardiogram
worked with researchers leading the University
of California San Francisco’s Health eHeart study
to develop a ResearchKit-based study of their own called
mRhythm. On
Thursday, Cardiogram and UCSF’s cardiology division are
presenting the results of that 14-month study, which collected
more than 100 million heart rate data points from more than
6,000 Apple Watch users. Cardiogram developed a machine
learning-powered algorithm that can detect atrial fibrillation,
which is often asymptomatic.

Cardiogram’s algorithm was tested against an in-hospital test
called cardioversion. Patients experiencing atrial
fibrillation, which affects one in four people in their
lifetime and causes 25 percent of all strokes, wore an Apple
Watch while undergoing cardioversion to compare outcomes. Both
segments, the cardioversion test and the Apple Watch’s heart
rate data, were blinded against whether the patients’ heart
rates were normal or abnormal, then sent to Cardiogram’s
algorithm. The results: the Apple Watch data detected atrial
fibrillation 97 percent of the time.

Cardiogram developer Brandon Ballinger said the results were
surprising.

“I don’t think anyone would’ve expected at the beginning of
this study that a product you can just walk into an Apple Store
and purchase would have 97 percent accuracy,” Ballinger told
Macworld. “Apple did a fantastic job with the sensor.”

Does that mean the Apple Watch’s optical heart rate sensor is
always accurate? Not exactly, said Dr. Gregory Marcus, director
of clinical research for UCSF’s cardiology division and lead
researcher for the eHeart study.

They’re “sufficiently accurate so as to distinguish a
consistently irregularly regular rhythm,” Marcus said.

Basically, the beats per minute as displayed on the watch
screen may not be precise, but the sensor can accurately detect
irregularity in those beats.

“If you had a certain rate of inaccuracy, presumably on a
population level that would be fairly consistent,” Marcus said.
“As long as that’s not markedly different, it shouldn’t really
matter as long as intermittently it’s getting it right. We’re
not using it to tell us what the actual heart rate is, we’re
using it to help us discriminate between a normal rhythm and
atrial fibrillation.”

The future of health apps

The fact that Cardiogram has leveraged the Apple Watch’s heart
rate data to develop an algorithm that can accurately detect an
early symptom of heart disease is major. Apple CEO Tim Cook has
said that Apple isn’t interested in submitting the watch for
approval from the U.S. Food and Drug Administration, which
would significantly slow down the speed of hardware
development. But Cardiogram’s Ballinger said he’s interested in
testing the algorithm his team has developed more extensively
and eventually submitting it for FDA approval, so Cardiogram’s
watch app will be able to alert users when they should see a
doctor.

“I think health will be the dominant use case for Apple Watch
and other wearables,” Ballinger said. “The average user of
Cardiogram opens the app about five times a day. Heart rate
data reflects everything that happens in your life. People use
it for medical conditions but also everyday things like, ‘How
well am I sleeping?’ or, ‘How stressful was this meeting?’ When
I show this data to people it usually resonates with them. They
say, ‘Oh, I had no idea you can find out all of this stuff from
the watch’s heart rate sensor.’ In 10 years it’ll be silly to
not have a heart monitor.”

Cardiogram’s current watch app uses your heart rate data to
offer lifestyle insights, as other health apps do. But in the
not-too-distant future, health apps like Cardiogram will be
much more powerful.

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