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Apple Watch ECG app: What cardiologists want you to know

We've read the fine print -- and consulted experts -- about Apple's irregular heart rhythm technology so you don’t have to.

Danielle Kosecki
Danielle Kosecki is an award-winning journalist who has covered health and fitness for 15 years. She's written for Glamour, More, Prevention and Bicycling magazines, among others, and is the editor of The Bicycling Big Book of Training. A New York native, Danielle now lives in Oakland where she doesn't miss winter at all.
Danielle Kosecki
7 min read

To take an ECG while wearing an Apple Watch Series 4, all you have to do is touch a finger on your opposite hand to the Digital Crown.

James Martin/CNET

Last year, to much fanfare, Apple announced two new additions to the Apple Watch . There's an ECG app exclusive to the Series 4 that can indicate whether your heart rhythm shows signs of atrial fibrillation (AFib) -- the most common type of irregular heartbeat and a major risk factor for stroke -- and the irregular heart rhythm notification (for all Apple Watches) which will alert you of irregular heart rhythms suggestive of AFib. 

Heart disease and stroke, despite being preventable, remain the leading cause of death for both men and women in the US, so it makes sense that people would be eager to adopt any sort of preventative heart-related technology. Stories about the Apple Watch's ECG feature saving lives certainly haven't hurt either.

But how helpful are these AFib features really? And are they right for you or a loved one? If you're considering buying a Series 4 -- or holding out for a Series 5 -- just for the ECG app, here are a few things cardiologists want you to know. 

AFib is a serious problem, but probably not among Apple Watch wearers

Sales research from the NPD Group shows that adults aged 18 to 34 are buying smartwatches more than any other age demographic. And EMarketer predicted that in 2019 consumers aged 25 to 34 will remain the largest group to purchase wearables. 

Contrast that with the fact that the CDC estimates AFib affects somewhere between 2.7 million and 6.1 million Americans, but the majority of those people are over the age of 65. In fact, only approximately 2% of people younger than age 65 have AFib and it's estimated that only 1% of the population may have undiagnosed AFib. In the latter two groups, AFib episodes are often brief, cause no symptoms and may not require treatment. 

Watch this: We tested the Apple Watch EKG against a hospital EKG

This is all to say that if you're young, healthy and don't already have any diagnosed health problems, you might not experience significant benefits from the ECG app, or the watch's other heart rate features. However, the Apple Watch has, on multiple occasions, alerted people both young and old about heart issues they didn't know existed.

Experts are unsure whether widespread screening for AFib is beneficial

The American Heart Association and the American Stroke Association has found that screening for AFib in the primary-care setting among people older than 65 years of age using pulse assessment followed by ECG, if warranted, can be useful. 


The Apple Watch Series 4 puts a one-lead ECG on your wrist.


But when the US Preventive Services Task Force weighed the potential benefits (early detection) against the potential harms (misdiagnosis, additional testing, invasive procedures and overtreatment), it found that the available evidence was too inadequate to support a conclusion one way or the other.

And because most of the AFib and stroke prevention studies have focused on the older populations who are most at risk, even less is known about the value of screening for AFib in healthy individuals under age 65. For instance, Dr. Venkatesh Murthy, professor of preventive cardiology at the University of Michigan, estimates that 90% of irregular rhythm alerts in younger groups are false alarms. 

As a result, experts worry that putting Apple's screening technology on the wrists of millions of people who are likely to be young and healthy could increase the risk of overtreatment. Especially when that technology is still so new and based on studies that haven't been published in peer-reviewed journals. You can read some of the comments from the medical community here, here and here.

"I'm an advocate of identifying asymptomatic atrial fibrillation, especially in high-risk populations," says Dr. Anthony Pearson, a Missouri-based board-certified cardiologist. "But we have to have a highly sensitive and specific way of doing it. In the younger population, if they don't have two or more risk factors [for stroke] then identifying them is nice but it's not going to prevent a stroke." 

The Apple Watch is not a replacement for medical care

The Apple Watch can be a useful tool for monitoring your heart health, but it has limitations.

It's able to check your heart rhythms, or the electrical impulses that coordinate your heartbeat, for any irregularities. Occasionally throughout the day -- about every two hours, depending on your activity levels -- the Apple Watch will check your heart rhythms, looking for arrhythmia, which occurs if these impulses don't work properly, causing your heart to beat too fast, too slow or irregularly. If the Apple Watch detects signs of an irregular rhythm five out of six times in a row within 48 hours, you'll receive an irregular rhythm notification. 


Sample screens from the Apple Watch Series 4's ECG app.

Screenshot by Amanda Capritto/CNET

The Apple Watch can also detect possible AFib via its ECG app. This feature replicates a single-lead ECG with a titanium electrode in the watch's Digital Crown and a layer of chromium silicon carbon nitride on the back of the watch. When you place your fingertip on the electrode, it creates a closed circuit from finger to heart to wrist and allows the watch to record the electrical impulses that make your heart beat.

While these features are a big step in giving everyday consumers access to preventative medical tests outside of the doctor's office, neither of these methods are a replacement for going to the doctor or using any monitor that your doctor may give you (and Apple agrees). Here's why:


CNET Senior Editor Vanessa Hand Orellana gets hooked up to a 12-lead ECG. 

James Martin/CNET

To properly diagnose when someone is in AFib, doctors use 12-lead ECG machines. (Doctors in the US usually call them EKGs, but it's the same thing, an electrocardiogram.) They use electrodes placed on different parts of the body to evaluate the heart's electrical activity in three directions (right to left, up and down, and front to back), which provides a clearer picture of its movement through the heart's four chambers. 

Because AFib is known to come and go, if it's not present during an appointment, a doctor may ask a patient to wear a simplified version of the 12-lead ECG at home so they can monitor their heart rhythms over a longer period of time. However, even these mobile monitors typically use two to three leads and run continuously over days, weeks or even months, says Murthy. 

AFib is the only heart issue the ECG app can detect

A woman recently wrote to Dr. Pearson, the cardiologist, asking whether the Apple Watch could help detect a future heart attack in her husband, who had already had one at age 36. "The answer is a resounding and unequivocal NO!" Pearson responded via his blog, The Skeptical Cardiologist.

The Apple Watch can only detect irregular heart rhythms, which are a risk factor for stroke. As Apple's website states: The ECG app can't detect a heart attack, blood clots, stroke or other heart-related conditions, including high blood pressure, congestive heart failure, high cholesterol or other forms of arrhythmia. 

These irregular rhythm features aren't for everyone

Apple's main disclaimer about the ECG app is that it should only be used by people 22 years old or above. But it also states that heart rates under 50 or over 120 beats per minute can affect the app's ability to check for AFib, leading to inconclusive results. 

Low heart rates are common among fit, athletic individuals, but can also be caused by certain medications. High heart rates may be caused by exercise, stress, alcohol, dehydration, infection or AFib itself. 


Using the Apple Watch Series 4 ECG app in conjunction with the Apple Health iOS app.

Screenshots by Jason Cipriani/CNET

The irregular rhythm notification feature is only cleared for use in people who are at least 22 years old and have no prior history of AFib. Apple is also careful to point out that the watch is not constantly looking for AFib, stating, "This means the Apple Watch cannot detect all instances of AFib, and people with AFib may not get a notification." 

The Apple Watch's ECG app isn't your only option

Portable and home-based ECGs are becoming increasingly common and have the potential to transform medical care, according to a 2018 study in the Journal of Arrhythmia. But, as the study authors note, research supporting their accuracy and ease of use is still scant. 

If you think you could benefit from an at-home ECG monitor, talk to your doctor about whether that strategy is right for you and what device they'd recommend.

Pearson has been using AliveCor's KardiaMobile single-lead ECG device with dozens of AFib patients since 2013 and Kardia Pro, a cloud-based software platform that allows him to monitor their results, since 2017. He says the combination is "eliminating any need for short- or long-term cardiac monitors."


The Kardia Mobile takes your ECG via small finger pads, which you can attach to the back of your iPhone.


"It's like night and day how much more information I get and how I'm able to manage their atrial fibrillation without bringing them into my office or an emergency room or putting expensive monitors on them," says Pearson, who does not receive any compensation from AliveCor. "It's dramatic how improved my care is with these devices."

Last month, AliveCor also launched KardiaMobile 6L, the first FDA-cleared direct-to-consumer six-lead ECG. It can detect AFib, bradycardia (abnormally low heart rate), tachycardia (abnormally high heart rate) and more.

The bottom line

If you're healthy and haven't been diagnosed with AFib or any conditions that put you at risk for it -- such as high blood pressure, diabetes or heart failure -- Murthy says the best thing you can do to take care of your heart is to follow what the American Heart Association calls Life's Simple 7. "Exercise, eat right, stop smoking and lose weight. If you have high blood pressure, high cholesterol or elevated blood sugar, manage that under the care of a doctor." 

If an Apple Watch can help you or motivate you to do those things, great. If not, using one isn't necessary. 

If you've already been diagnosed with AFib or are experiencing prolonged periods of heart palpitations or a racing heartbeat, talk to your doctor about whether at-home monitoring is right for you. For now, both Murthy and Pearson are holding off on recommending that their patients get an Apple Watch solely for its irregular heart rhythm features. 

"I generally recommend devices that can record continuous ECGs over long periods of time rather than the intermittent snapshot of the Apple Watch," says Murthy. "That said, future data may help us decide if that's necessary or if intermittent ECGs coupled with photoplethysmography-based rhythm monitoring [like what the Apple Watch does]is sufficient."

Note: The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives. 

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.