Apple Watch: How to Take an ECG Reading

A Guide to Using Apple Watch's Heart Rate Features, Including ECG

Apple

One thing that makes smartwatches increasingly valuable is their inclusion of biosensors, little modules that keep tabs on what's happening with your body, whether you're an athlete running a marathon, or somebody who just decided to get up off the couch. And one of the most useful health metrics a smartwatch can track is your heart rate. Apple knows this, and, as part of an effort to make the Apple Watch a more alluring accessory for iPhone owners, the company is focusing intently on building advanced heart-rate monitoring into its best-selling wearable.

A software update rolling out today will include an optional app for Apple Watch Series 4 that takes ECG (electrocardiogram) readings through the new device's specially designed sensors. That same software update will allow older Apple Watches without the redesigned sensors to detect irregular heart rhythms. Both of these enhancements are supposed to help wearers identify signs of atrial fibrillation , a condition identified by a rapid or irregular heartbeat that can lead to serious heart complications.

Apple made a splash when it announced these features at its annual hardware event in September, partly because the ECG app had been cleared by the FDA (which, it's worth keeping in mind, is different from FDA approval). But, even if you don't have the latest hardware and can't take advantage of the ECG app, there are plenty of heart-rate tracking features to dive into on the Apple Watch. It's a lot; here's a short guide.

Heartware Limitations

Let's start with the basics: the ECG app and notifications around irregular heart rate rhythms are rolling out as a part of a watchOS update for Apple Watch. The latest software is watchOS 5.1.2. Apple Watch updates can take an extremely long time for such a little gadget—you may wait more than an hour—and at the time of publication, I hadn't installed the update myself yet. My experience with the ECG app was on a loaner watch Apple provided. But hopefully, the update process has improved.

The ECG app will only work on Apple Watch Series 4. That's because that watch has electrodes built into the back of the watch, as well as electrical heart sensors in the watch's crown. Older Apple Watches don't have this.

All Apple Watches, however, do have the same optical heart rate sensors. That means that, with this latest software update, Apple Watch Series 1 and later watches will attempt to track irregular heart rhythms, and therefore will potentially be able detect atrial fibrillation.

How to Use the ECG App

Before you start using the ECG app on the Apple Watch Series 4, you'll have to first go through the onboarding process in the Apple Health app on iPhone. Same with setting up notifications for possible signs of Afib. It requires scooting back and forth between the iPhone's Watch app, the iPhone's Health app, and the Apple Watch itself. But once the setup is done, you shouldn't have to go through it again.

Apple has made a point to say (many times) that the ECG app is not a diagnostic tool; and that it's really not supposed to be used just for kicks. You're supposed to give it a go when you're feeling symptoms like a rapid or skipped heartbeat. Or, you can use it when you get a notification that the watch has detected an especially high or low heart rate, or some other irregularity.

That said, taking an ECG reading is straightforward. You open the ECG app on the Apple Watch, rest your watch-equipped arm somewhere, and press the index finger of your opposite hand against the Apple Watch's crown for 30 seconds. Occasionally, it might say recording stopped due to a poor reading, which happened to me a couple times when the watch's underside wasn't flat against my wrist—so make sure the back of the watch is in full contact with your wrist. The app then shows results right on the watch; for example, it might say it detected a sinus rhythm, which means your heart is beating in a uniform pattern. It also shares the findings with your iPhone's Health app.

So far, in the time that I've been wearing the loaner Apple Watch with the latest software, I haven't received an irregular heart rhythm notification. And there's really no way to "test" whether it's accurate if I don't have the problem it's looking for. Using the ECG app is an active experience. You open the app on Apple Watch and take that 30-second reading. The irregular heart rhythm detection, on the other hand, is a passive thing; you'll only get a notification if the watch detects a problem after taking multiple background readings.

Exercise Your Options

One of the key features to look for on any wrist-based tracker is its ability to measure your spikes in heart rate during intense exercise activities. The Apple Watch has done this since the product's origin, though over time, the company has tweaked the way the device tracks your heart rate during periods of exercise.

The Apple Watch can't diagnose you with anything. It's supposed to point you toward meaningful data and maybe encourage you to act if there are signs something may be wrong.

For example, with the rollout of watchOS 4 in 2017, the Apple Watch starting showing a "Workout Recovery Rate" after an exercise session. This bit of data lets you know how quickly your heart returns to its regular resting rate after a workout. You'll have to actually record the workout on the watch (using the green Workout app) in order to see your recovery rate, though. After that, it's not easy to find. After ending the workout, you have to scroll down through the workout summary and tap on the tiny heart icon, which brings you to the Heart Rate app. Your recovery rate can be found there.

Over the last few years, Apple has also upped the watch's sampling rate—its frequency of heart-rate measurements, which are taken automatically in the background as you go about your business. A software update in September 2016 changed the all-day sample rate from once every ten minutes to once every five minutes. Apple won't share specifics on how the sample rate during exercise routines has changed in this watchOS update, but fitness wearables are often designed to sample heart rate most frequently when you indicate that you're exercising.

Rest(ing) Up

The Apple Watch will also show you your resting heart rate, although my understanding is that Apple's approach is different from heart rate monitors that are designed to be worn overnight. That's the thing about Apple Watch, and one of my biggest quibbles with it: Because its battery only lasts between a day and a day and a half, it's not really meant for tracking your sleep. You can't get an overnight or a first-thing-in-the-morning heart rate reading if your watch is on the charging pad atop your nightstand.

Instead, the watch will sample your heart rate once you're wearing it, and continue to measure it until it has sampled enough to algorithmically determine a resting heart rate reading. Sometimes this means it won't appear until after you've worked out or arrived at work.

All Day Every Day

Even if you're not interacting with your Apple Watch's heart rate features directly, the Watch is periodically taking those background readings. It will record your average resting rate as well as your walking average heart rate. In watchOS 4, it also started recording heart rate variability, or any variation in the time between heartbeats, a few times a day.

And if you just want to check out your current heartbeat from time to time, or compare it to a reading from a pulse oximeter in a doctor's office like I did recently for fun, you can do that by tapping on the heart rate app (a gray app with the red outline of a heart) on the Watch.

Appsolutely Healthy

If you're really interested in diving into the Apple Watch's heart rate tracking features, plan to spend a lot of time in the Health app and the Activity app, both on the iPhone. This is where all the health data from the watch eventually goes, and there are just limitations around how much granular data you can view on a tiny little wrist computer.

The easiest way to get there in the Health app is to open the app and go to the Health Data tab, next to the Today tab, on the bottom of the app screen. Then go to Heart (third menu option) and you can see your heart rate data by category and also by hour, day, week, month, and year.

On the Watch itself you can see what your heart rate was during an exercise session that occurred that day. But reviewing your heart rate from a historical workout session is a bit more complicated. For that, you'll have to go to the Activity app on your iPhone; select the day; scroll down to Workouts, tap on that; and there you'll see a graph of your heart rate during that particular activity.

Doctor's Orders

The Apple Watch (and really, any smartwatch or wrist wearable that's sold directly to consumers) comes with so many health-tracking caveats that there are too many to list here.

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The most important thing to remember is that the Apple Watch can't diagnose you with anything; it's supposed to point you toward meaningful data and maybe encourage you to act if there are signs something may be wrong. The Watch alone can't tell you if you have Afib. In fact, as you take an ECG reading, the app displays a warning the whole time "Note: Apple Watch never checks for heart attacks."

Sure, there have been scattered stories about Apple Watch notifications alerting people to an abnormally high heart rate and saving lives . But you shouldn't rely on just the Apple Watch, or any smartwatch, if you're seriously concerned about your heart health.

WIRED's own Robbie Gonzalez has written a great explanation of the level of preclinical research that went into the Apple Watch's ECG app and irregular heartbeat detection features. Again, these are really more about recording data that can be shared with a physician then they are about alerting you on the spot.

The other caveat involves accuracy. When it comes to tracking heart rate during vigorous exercise, for example, wrist wearables aren't always dead-on. A 2016 study conducted by the Cleveland Clinic using four popular wrist-wearables showed variable results. (Fitbit was even sued at one point for what the plaintiffs said were inaccurate heart rate readings during exercise; Fitbit has since improved its heart rate tracking.) In a 2017 study conducted by Stanford University researchers , the Apple Watch achieved the lowest overall error rate in heart rate monitoring, compared to six other wearables. However, none of them measured energy expenditure very well, the researchers found. With all that said, the Apple Watch is still pushing the boundaries on what your basic wrist-worn wearable can do. And it's these kinds of health-tracking features that might make someone who once scoffed at the idea of a smartwatch actually consider one now.

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