Apple Watch Series 4 with ECG function turned on.
Photo: Apple

Apple says its new smartwatch’s ability to take an electrocardiogram (EKG) could be a game-changer for people with heart conditions. And the device has been cleared for use by the Food and Drug Administration. But some experts say a consumer EKG device can carry risks, as well.

The feature, originally announced this past fall, finally rolled out Thursday in the form of a software update for the Apple Watch Series 4.  

An EKG measures the electrical activity of the heart. Even if the watch functions as advertised, the experts say, it can be counterproductive to have consumers collecting their own hard-to-interpret diagnostic data.

“It’s hard to comment on the usefulness when there’s been no data on its accuracy or whether it improves outcomes,” David L. Brown, M.D., a cardiologist and professor of medicine at the Washington University School of Medicine in St. Louis, Mo., said when Apple first introduced the idea in September.

“Apple and the FDA are basically asking us to assume it’s going to be helpful. But there’s no data and a lot of scenarios where it could be harmful.”

How it Works

The Apple Watch Series 4 has a number of health functions. It is supposed to help people work out more efficiently and can lead them through breathing exercises. According to the company, it can also detect a fall and summon help, if necessary.

More on Apple and Smartwatches

But the watch also crosses over into areas usually reserved for medical devices. The watch measures heart rate patterns and is supposed to alert a consumer if his or her heart rate spikes or becomes abnormally low. Some of these capabilities were built into previous versions of the watch, using the type of optical heart rate sensor found on a number of smartwatches and fitness trackers.

The Series 4 has an optical heart rate sensor, but it adds a new sensor, housed in the little dial on the side of the watch, along with new electrodes on the back of the watch. Together, they can take an EKG if the user presses the dial with his finger for about 30 seconds.

Among other functions, the watch is supposed to detect signs of atrial fibrillation, a type of irregular heart beat (also called arrhythmia).

That condition, which generally affects older people, can increase a person’s risk of stroke, so people diagnosed with it are often treated with blood thinners to prevent one, says Brown of Washington University. (About 1 percent of the U.S. population has atrial fibrillation; 70 percent of those cases are in people age 65 and older.)

To install the new feature on your watch, look for a software update in the General section of your Apple Watch app. After you download and install the software, you’ll see the new EKG app on the watch’s app screen. To set it up, open the Health app on your phone and follow the instructions. A short tutorial will walk you through how to take your first EKG.

Keep in mind, however, that EKGs are only recommended for people who have a high risk of heart disease, suspected heart disease, or symptoms such as chest pain or shortness of breath. And if you fall into one of those categories, you should probably talk to your doctor about setting up an EKG.

EKG recordings taken on the Apple Watch are stored in the Health app and can be shared with your doctor. You can also set your watch to take recordings in the background and notify you if it detects possible atrial fibrillation. Those results are also stored in the app.

Descriptions on Apple's website claim the watch's "revolutionary health capabilities" will empower individuals to "have a better-informed conversation" about their health with medical professionals.

Worries About False Positives

Many medical professionals don’t recommend EKGs for people who don’t have symptoms of heart disease, such as chest pain or shortness of breath.

The U.S. Preventive Services Task Force (USPSTF), an independent panel of national experts who offer evidence-based guidance about preventive health practices, says a false positive on such a test can lead to unnecessary follow-up tests or treatments that come with their own risks.

Any time you do such testing in a group that’s low-risk, Brown says, you tend to get more false positives than actual positives. That could mean that many Apple Watch owners who decide to use the EKG function and fear they are suffering from atrial fibrillation could be perfectly fine. 

If those users decide to go to an emergency room, he says, doctors might order extra tests, out of an abundance of caution, or even start that person on blood thinners. In a worst-case scenario, those potentially unneeded medications could cause serious bleeding, or even death, if that person happened to fall.

“In the worried, well population, it’s going to be of no benefit," Brown says. 

In its letter clearing Apple’s EKG app for over-the-counter use, the FDA said that the device is for “informational use only,” and that it’s “not intended to replace traditional methods of diagnosis or treatment.”

Who it Might be Good For

However, doctors say these watches may prove useful for some people with known or suspected cardiac conditions.

James Brophy, M.D., a cardiologist and professor of medicine and epidemiology at McGill University, said in September that many people with heart palpitations are investigated for arrhythmias. They often have to wear large, bulky heart monitors for a day or two, but doing that often doesn’t lead to a diagnosis.

“However, imagine that the patient has symptoms, they can immediately get an EKG, and if normal, this can reassure them,” he says. “Alternatively, the EKG may show something like atrial fibrillation, leading to appropriate therapy.”

In addition, Brown says it’s not uncommon for patients who have had surgery to go into atrial fibrillation from the stress of the procedure. Usually, long-term treatment is not required, but monitoring using the Apple Watch could eventually prove to be useful, he adds.

In addition, Brown says the feature could be good for monitoring the conditions of people with known atrial fibrillation that’s being controlled by medication. It could let doctors know whether they’re going back into atrial fibrillation and whether their medication needs to be adjusted.

But that use is not currently recommended. The FDA, in its letter to Apple clearing the notification feature, specifically said that the feature isn’t intended for use by people who already have an atrial fibrillation diagnosis.