The Apple Watch Series 4 takes heart monitoring to next level

Its new EKG feature isn’t active at launch, but the Apple Watch is already proving to be a game-changing home health monitor.

Vanessa Hand Orellana CNET Senior Editor
As head of wearables at CNET, Vanessa reviews and writes about the latest smartwatches and fitness trackers. She joined the team seven years ago as an on-camera reporter for CNET's Spanish-language site and then moved on to the English side to host and produce some of CNET's videos and YouTube series. When she's not testing out smartwatches or dropping phones, you can catch her on a hike or trail run with her family.
Vanessa Hand Orellana
7 min read
James Martin/CNET

It's not often that the announcement of a new iPhone -- let alone three of them -- is overshadowed. But by the end of Apple's big fall hardware event on Sept. 12, it seemed like the new Apple Watch Series 4 had stolen the show.

Four years and five versions since its September 2014 unveiling, the Apple Watch isn't just among the best-selling smartwatches, it's said to be the top-selling watch brand, period. And for 2018, the company is leaning in to that success with its first big redesign to date. The Series 4 boasts a thinner body, a bigger screen, a faster processor and -- on the high-end model -- a stronger LTE signal, so you can leave the iPhone at home on those early-morning runs.

Read: Apple Watch Series 4: Review in progress

But the price tag of new models has edged up, too, with the new model starting at $400. So how is Apple enticing existing users to upgrade -- and new users to take the first-time plunge? Simple: It's making the Apple Watch a must-have health companion with a first-ever built-in electrocardiogram (EKG or ECG).

By adding the EKG feature, the Apple Watch has gone from a smart fitness tracker to a potentially life-saving medical device that will soon be able to warn wearers of abnormal heart rhythms associated with atrial fibrillation and other serious medical conditions.  

"We estimate that there are almost 700,000 undiagnosed cases of AFib in the United States, and most of them would benefit from treatment such as anticoagulation to prevent stroke," says Dr. Mintu Turakhia, executive director of Stanford University's Center for Digital Health.

Apple Watch Series 4: Both sizes, compared

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Imagine, then, if those hundreds of thousands of people had an EKG-capable Apple Watch that could get them on the road to such treatment faster. Even previous pre-EKG Apple Watch models have already been flagging major, potentially life-threatening heart problems. Many of the beneficiaries are younger, seemingly healthy users who would've never suspected they had any kind of serious medical issues in the first place.

In fact, the Apple Watch has already started crossing over into the realm of medical monitor, whether users -- and doctors -- are ready or not.

Watch this: Apple Watch Series 4: Bigger screen with EKG sensor

Apple's heart history  

Heather Hendershot was on the couch watching TV with her husband when her Apple Watch started beeping. The notification said her heart rate had spiked over 120 beats per minute, well above the normal resting heart rate for a healthy adult. The 26-year-old mother of two ignored the first one, but the watch kept beeping.

"I thought the watch had to be wrong because I couldn't feel my heart racing," says Hendershot. "My body was not giving me any signals."

After monitoring her heart rate overnight with the same results, Hendershot decided to take a precautionary visit to urgent care in Topeka, Kansas the next morning.

Apple Watch version 4 EKG heart health  apple-event-091218

Apple COO Jeff Williams announced the EKG feature of the Apple Watch 4 on Sept. 12.

James Martin/CNET

"It wasn't until they mentioned ICU [Intensive Care Unit] that I realized how serious the whole situation was," she says.

Doctors diagnosed her with hyperthyroidism, a condition where the thyroid gland produces excess thyroxine hormone, and that if left untreated, could lead to life-threatening complications.


The Apple Watch alert that appeared on the iPhone of ZDNet's Jason Perlow.

Screenshot by Jason Perlow/ZDNet

Heather's story is just one of many -- from Florida teenager Deanna Recktenwald to Jason Perlow, a writer a CNET's sister site, ZDNet -- in which the heart rate feature on the Apple Watch, or other wearable trackers for that matter, have helped clue in users of serious medical problems. Like Heather, many of them considered themselves perfectly healthy, with no history of heart related conditions.

Heart rate tracking has been an important feature of the Apple Watch since the wearable it was first announced four years ago in September 2014. But up until now it had been primarily used for fitness -- say, keeping at a certain level while you're on the treadmill. It's a fundamental measurement, alongside distance and pace to calculate calories burned during exercise.

With the release of WatchOS 4 last year -- the spinoff of the iPhone operating system that powers the Apple wearable -- the Apple Watch became proactive about heart rate with the Elevated Heart Rate Notification, an opt-in feature that alerts users when their heart rate peaks for at least 10 minutes during a period of inactivity. It was that feature that flagged Heather's condition.

But there's a big difference between noticing a high heart rate and actually screening for diseases. To do the latter, wearables like the Apple Watch needed to reach a medical grade level of precision that would require a different type of sensor.

Watch this: Apple adds EKG monitoring to new Watch 4

Becoming a medical device

When it comes to measuring heart rate, the EKG is considered the gold standard. It measures the electrical signals generated by the contraction of the heart muscle through a series of electrodes placed on the chest of the patient. Physicians then use this information to detect abnormalities in the rhythm and structure of the heart, up to and including the diagnosis of a heart attack.


An EKG machine shown at the Human Performance Center at UCSF. 

James Martin/CNET

Fitness trackers and smartwatches like the Apple Watch made heart rate data available on the wrist 24/7, but measure blood flow instead of electrical activity. To fit on the wrist, they use a sensor called a photoplethysmogram (PPG) which uses light to determine how much blood the heart is pumping under the surface of the skin.

Dr. Turakhia says this measure is usually accurate for most normal conditions and normal rhythms, but it can lose accuracy under certain conditions.

Movement is one of the variables that can interfere with a good read. While resting heart rate tends to be spot-on, the sensor may have a harder time getting an exact read during high-impact activities when the watch is bouncing up and down the wrist. Tattoos can also interfere with a reliable read as they may block the light from penetrating the skin.

For average consumers looking to increase their general fitness level, the drawbacks of PPG technology may be acceptable. But to cross over into the medical realm and screen for serious conditions like AFib, these wearables needed to improve accuracy and get FDA clearance.


Before the Series 4 came along, Apple Watch users who wanted clinical grade readings could purchase the AliveCor KardiaBand, a $200 watchband with an EKG. It was the first FDA cleared accessory for the Apple Watch to detect abnormal heart rate using and prompt users to take an EKG to share with their doctor. (FDA cleared is a federal health certification that's one notch below FDA approved.)

With the Series 4, Apple has cut out the middleman and built the feature right into the Watch. Instead of having a sensor on the band, the Series 4 has electrodes on the digital crown and on the electrical heart rate sensor on the back of the watch. Once in the ECG app, the user just places his finger on the digital crown to get a read. After 30 seconds the watch lets the user know if the results were normal or of they have signs of AFib.

"It doesn't give you as much information as a full 12-lead EKG, but it's richer data than a simple pulse recording," says Dr. Gregory Marcus, a cardiologist and director of clinical research at UCSF.

Like the KardiaBand, the EKG feature on the Apple Watch Series 4 is FDA cleared. But the functionality isn't available on day one when the Series 4 launches on Friday, Sept. 21. Apple says it's coming "later this year." The only new heart feature it will have out of the box is the low heart rate alert that lets you know if your heart rate drops below a certain level.

In the meantime, competitors could be closing in. Fitbit, Samsung and Verily (like Google, a subsidiary of Alphabet) were among the nine companies, along with Apple, selected for the FDA's precertification pilot program. The program is designed for companies that want to speed up the clearance process for software for medical devices.

Fitbit and Garmin have also paired with medical institutions to conduct their own studies about the accuracy of their devices in screening for diseases. Neither company has an EKG feature, but they have added a pulse oximetry sensors to their newer devices that can measure the amount of oxygen in the blood. Paired with heart rate data, this information could help detect sleep-related issues like sleep apnea, asthma and allergies.

Watch this: iPhone XS, iPhone XR, Apple Watch: A closer look at Apple's new lineup

Reading into it 

But even once the feature is ready, putting all that heart information into the hands of consumers may have its downsides.

"One concern is that these fitness trackers can cause undue alarm," says Marcus. According to Marcus, a low or elevated heart rate doesn't always mean there's a problem, as it can also be triggered by other factors such as stress.

Take the 2018 NFC divisional playoffs, for example. The game between the Minnesota Vikings and the New Orleans Saints had fans at the edge of their seats and Apple Watches on high alert. Users on Twitter began posting pictures of their Elevated Heart Rate notifications while they were sitting on the couch watching the game. 

Marcus says the benefit of the Apple Watch Series 4 is that it can provide valuable EKG information for the doctor to consider alongside the notification. "Ultimately the physician is the only one that can make an accurate diagnosis using the primary image from that EKG," he says.  

False alarms aside, the heart feature could ultimately speed up the diagnostic and catch a problem before it gets out of hand particularly for people like Hendershot who are otherwise unaware they have a problem.

"If it wasn't for the watch, I would not have gone to see a doctor," says Hendershot. I am not someone who checks their heart rate randomly, and I wasn't showing any other symptoms".

For Turakhia, as for Marcus, the biggest question isn't how to listen to your heart, it's what do with the information. "Is there benefit to having the diagnostic conveniently as part of your regular life?" he asks. "I think that's the central question that all of us are excited about."

The Apple Watch Series 4 is available for preorder now and will be in stores on Sept. 21. It comes in aluminum or stainless steel and in a 40mm and 44mm case size and starts at $399. 

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