The Apple Watch ECG has detected something strange about my heart rate


When I started testing the new EKG feature on the Apple Watch Series 4 – available on Thursday through the free service Watch OS 5.1.2 software update – the last thing I expected was to find something abnormal in the rhythm of my heart. But that's exactly what happened when I was crossing the clock readings with medical grade ECG equipment in the doctor's office.

"We see on your Apple Watch the same heartbeat that we see on the electrocardiogram," said Dr. Gregory Marcus, a professor of cardiac medicine and electrophysiology at UCSF Medical Center, sitting on the hospital bed with cables attached to my body and a Apple Watch Series 4 on my wrist.


Results from the Apple Watch EKG showed the same irregular beat as the doctor's ECG.

James Martin / CNET

"These initial beats are very common … but they can lead to long-term problems, so we should talk a bit more about it," he added.

Heart rate tracking has always been a big part of Apple Watch and fitness trackers in general. But so far, it has been used mainly for activity tracking and calorie counting.

With the update to Watch OS 5.1.2, heart rate will play a bigger role in Apple Watch as we gain access to the two new features released by the FDA that Apple announced in its September lecture. There is an abnormal heart rate alert for all Apple Watches, except the first generation model, and a Series 4 ECG or EKG. Both can help alert you to potentially fatal heart conditions.

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We tested the Apple Watch EKG against an EKG hospital


Heart Rate Measurement

Heart rate tracking is nothing new for wearables. Smartwatches and fitness trackers have for years used LEDs and optical sensors in the back to measure changes in blood flow beneath the surface of the skin, also known as a pulse. When the heart beats, more blood is pumped into the blood vessels absorbing more light. Between beats when there is less blood, more light is reflected back to the receivers of the watch.

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Set up irregular heart rate reporting from the Health application in Apple Watch Series 1 and beyond.


In 2017, Apple Watch became proactive about how it used heart rate information by adding high-clock heart rate notifications to the watch, which allowed users to know when their heart rate was above a certain level and later added notifications low heart rate. These notifications had already been helping users to detect serious conditions.

But the heart rate measures only beats per minute, or heart rate frequency over time and not the patterns between each beat, known as heart rate.

"You can have a regular rhythm that is very fast or very slow … And likewise, one can have an irregular rhythm that is of a normal rate which is very fast or very slow," said Dr. Marcus .

With the new Irregular Rhythm Notification, Apple Watch uses the optical sensor to measure heart rate and alert users when it detects an irregular pattern that may be atrial fibrillation (AFib), a type of arrhythmia that may increase the risk of stroke cerebral and other cardiac complications. This feature will only work for adults over the age of 22 and will not help if you have already been diagnosed with Afib.

EKG on the Apple watch

To make a definitive diagnosis, the doctor needs more information than the pulse can provide.

"Sometimes these beats are so early that the heart has not had enough time to fill, even though there may be an initial electric strike that is happening," said Dr. Marcus. "We would like to have an electrical confirmation of a diagnosis of atrial fibrillation before we decide to act on it and not base it on it generally, just in recording the wrist," he added.

That's where the electrocardiogram comes in. An electrocardiogram uses electrodes to measure the electrical activity of the heart. A hospital-grade electrocardiogram usually consists of 10 electrodes placed on different parts of the body. While the Apple Watch Series 4 has two: an electrode on the bottom crystal and an electrode on the digital crown.

"This 12-lead electrocardiogram shows what is happening electrically at the heart of 12 different perspectives, or 12 different directions, while Apple Watch offers the same electrical activity but really in only one direction," explained Dr. Marcus.


Apple Watch uses electrodes on the back and the digital crown combined with the ECG application.

James Martin / CNET

While looking at your monitor, I opened up the new ECG application (Apple uses the abbreviation ECG, while doctors usually say EKG) in the Apple Watch Series 4 to do my first electrocardiogram. I put my finger on the digital crown and waited while the screen counted for 30 seconds. Apple Watch rates your heart rate as AFib, sinus rhythm or inconclusive. My result: inconclusive.

The notification on Apple Watch also said that I should contact my doctor if I did not feel well or continued to get the same result. Users can share these results as a pdf with their doctors, but thankfully my doctor came to be by my side.

The electrocardiogram on Apple Watch coincided directly with the hospital ECG results that Dr. Marcus had printed. There were intermittent early beats coming from the lower chamber of my heart.

"This would be really useful to track this down or have the first realization that you have these initial heartbeats," said Dr. Marcus. "What's missing in the single lead Apple Watch is the information that tells us more specifically where exactly this is coming from."


The results of Apple Watch on the iPhone compared to the results of 12-lead EKG on paper.

James Martin / CNET

More information equals faster results

Dr. Marcus says I probably will not die because of what he found on my electrocardiogram, but he wants me to track my first heartbeat, something I probably would not have picked up without that kind of test. And for people with more serious heart problems, this can help doctors make a faster diagnosis and allow them to treat the problem more quickly.

"Some people feel that when they have atrial fibrillation, but a lot of people do not, so there is hope that we can detect those people who otherwise did not know they had atrial fibrillation," Dr. Marcus said.

Apple Watch is the only consumer-direct device with an integrated EKG. But there are other devices like Alivecor's FDA that has eliminated KardiaMobile and KardiaBand for Apple Watch, which give users access to an electrocardiogram outside the doctor's office. Apple watches competitors such as Garmin and Fitbit are also working to improve heart rate monitoring as more tech companies focus on health care as a way to give new life to wearables.

"The other side is that we recognize that there is a risk of false-positive results that can lead to undue anxiety," said Dr. Marcus.

Irregular heart rate notification is already available on all Apple Watches starting with Series 1 and can be configured in the Heart section of the Watch application. The EKG application is only available on the Apple Watch Series 4 and is only available in the US, although Apple expects to obtain regulatory approval for this feature in other countries later.

Read the following: How to Buy a Smartwatch or Fitness Tracker

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